research articles in rhinoceros

A Holistic Approach to Rhino Research

By sarah gilsoul.

As wild rhino populations face ongoing threats to their survival, the need to ensure the health and sustainability of managed populations in zoos grows. Yet, maintaining a thriving ex situ population does not come without its challenges as our understanding of rhino health and behavior, their reproductive challenges, and the impact of diet in managed care is not yet complete.  

A coalition of rhino scientists established the American Institute of Rhinoceros Science (AIRS) to tackle the scientific challenges for sustaining rhino populations through four research pillars: physical fitness, wellbeing, reproduction, and iron overload disorder.

The initiative is a partnership between the Cincinnati Zoo and Botanical Garden’s Lindner Center for Conservation and Research of Endangered Wildlife ( CREW ) in Cincinnati, Ohio; Disney’s Animals, Science and Environment in Orlando, Fla.;   George Mason University ; the South-East Zoo Alliance for Reproduction and Conservation ; the University of Stellenbosch in South Africa; and The Wilds in Cumberland, Ohio, which serves as the base of operations for the program. Funding for the initiative was provided by the Institute of Museum and Library Services (IMLS) . Through the IMLS grant, the Cincinnati Zoo and Botanical Garden appointed Dr. Parker Pennington as the on-site operations manager at The Wilds, serving as a driving force behind the AIRS program as well as being the reproductive pillar leader.

[Related story: Saving Rhinos with Science ]

2022 marked the completion of The Wilds’ first full year working in collaboration with AIRS. While the work is far from complete, this milestone provides an opportunity to reflect on a year of data collection.

Comprehensive Care at The Wilds

Due to The Wilds’ long history of collaboration with CREW and its notable success in rhino reproduction, the facility became a natural choice for AIRS as its base of operations. Despite the community’s challenges with reproductive dysfunction in rhinos, in 2022, The Wilds welcomed its 29th white rhino calf.

There are certainly some theories as to why The Wilds has seen so many births over the years. The rhinos are able to explore 130 acres of pasture and exhibit a wide range of natural herding behaviors during the warmer months. Southern white rhinos are also sensitive to phytoestrogens in their food and due to their freedom to graze for eight months out of the year, rhinos at The Wilds receive very little supplemental grain. It is possible that both the ample space and diet positively impact their reproduction.

“The Wilds has created the only fourth and fifth generation rhinos outside of Africa, so clearly, they’re very good at making rhinos,” said Dr. Pennington. “Through AIRS we want to understand what exactly enables them to be so successful.”

With this objective in mind, the reproduction pillar aims to understand the factors contributing to the varying levels of breeding success in rhinos across facilities. Recent research has revealed that a significant portion of the managed population does not ovulate regularly. Through hormone analysis and ultrasounds, researchers have found that some animals’ ovaries are inactive and others have active ovaries but are not ovulating. The pillar’s primary goals include the accurate classification of individuals who are not ovulating, the identification of normal cycling animals, and the establishment of measures of estrogen, which would offer insights into ovarian activity.

The goal of understanding reproductive success in rhinos is but part of the broader objective of AIRS to holistically manage rhinos. In addition to the part they play in reproductive research, the rhinos at The Wilds contribute to the physical fitness and wellbeing pillars.

When researching the physical fitness pillar, AIRS staff examine rhino measurements and the biomarkers that indicate important health information, such as sugar levels and heart rate.

Researchers have taken an innovative approach to tracking activity levels under different management regimes by using anklets, similar to Fitbits®, to monitor the movement of the rhinos over a set period of time. This data enables an understanding of individual activity levels and the potential correlation with overall health parameters.

While the wellbeing pillar also looks at activity, it shifts its focus to the individual personalities of rhinos and how social interactions might impact their welfare under different management conditions. Building upon the activity data gathered from the anklets, researchers track the type of movements that rhinos are engaged in, as well as their interactions with other rhinos and their keepers. Additionally, participating facilities complete a husbandry survey that provides insight into how the animals are managed and if that has any behavioral outcomes.

At The Wilds, rhinos have not been involved in the iron overload disorder pillar, as this syndrome is primarily seen in browsing species like black rhinos. However, significant research is underway in this area to find non-invasive biomarkers that can indicate the presence of excessive iron in the body.

While there are specific goals within each pillar, nothing happens in a vacuum. The project scale allows researchers to investigate rhino physiology at the intersection of these research areas.    

“How physically fit an animal is can have an impact on its wellbeing, which in turn can impact its reproductive success or failure,” said Dr. Terri Roth, vice president of conservation and science at the Cincinnati Zoo and Botanical Garden and director of CREW.

Alongside its contribution of data, The Wilds has served as a testing ground for AIRS’ research procedures. The program’s launch at The Wilds also involved the training of graduate students who now travel to participating institutions to acquire and collect data. The data collection follows a seasonal timeline, with each facility visited once during the summer and again in the winter. Independently, participants collect monthly blood samples for one year and are tasked with collecting weekly samples for 12 weeks in both the summer and winter seasons.

“Our rhinos have helped us figure out the best way to do certain procedures,” said Dan Beetem, director of animal management at The Wilds. “They’ve helped us figure out what works and what doesn’t before we go out and ask other facilities to do the same.”

Building the Momentum

AIRS is still far from finished. After a year of implementation at The Wilds, the facility still plans on enrolling the other half of its rhino herd into the program for another full year of research. Moreover, as new institutions continue to join the program, data collection will expand.

“The last year of this project is going to be a lot of pulling those pieces together,” said Beetem. “We’re going to be doing the data analysis, starting to write the manuscripts, and then coming up with care recommendations.”

The goal is to take all of the data collected from the AIRS studies and compile it into a centralized database accessible to all members. In addition to updated rhino care recommendations, participating members will be provided with reports specific to each facility and their rhinos, with information about how their animals compare to the rest of the population.

Although the study results are not yet known, AIRS researchers remain open-minded and optimistic.

“This project is a really great example of what we can do when we put our resources together,” said Dr. Jan Ramer, senior vice president of animal care and conservation at Columbus Zoo  in Powell, Ohio, and The Wilds. “Together, we can achieve a lot for the wellbeing of our animals.” 

Sarah Gilsoul is a writer and program assistant for communications at AZA.  

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• 04 July 2023

Without their signature horn, black rhinos are less social

• Engela Duvenage

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Dehorned black rhinos explore less, and retreat to more central parts of their home range

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Dehorning black rhinoceros ( Diceros bicornis ) to prevent poaching could have affect the behaviour and social lives of the endangered animals, data published in PNAS shows. Once dehorned, their home ranges shrink by an average of 45%, and their social interactions reduce by an average 37%. Bulls, in particular, interact less frequently with other males.

The study was conducted by researchers from the University of Neuchâtel in Switzerland and staff from various black rhino conservation groups and nature reserves in South Africa. The team analysed data from 4,760 sightings of 368 black rhinoceros between 2005 to 2020, in 10 reserves in northeastern South Africa.

The reserves have been targeted by poachers who kill the rhino for their horns, highly valued in east Asian countries for their supposedly medicinal properties. Some of the reserves practice dehorning, others not.

Black rhino live within specific home ranges. They are solitary, but because neighbouring home ranges overlap, they connect with others of their species.

“It’s as if they all feel less confident and vulnerable without a horn. Because they are generally solitary, they do not know that their neighbours are also dehorned. They explore less, and retreat to more central parts of their home range,” notes lead author, Vanessa Duthé, a PhD student at the University of Neuchâtel.

Duthé explains that maps of rhino movements clearly show how home range sizes are determined by whether an animal has a horn. The home range of dehorned animals shrunk on average by 11.7 km² (or 45.5%). The turf of dehorned females was on average 15.42 km² (or 53.08 %) smaller, and that of dehorned males 9.13 km² (or 38.03 %).

Duthé says it is still unclear how this will impact the species’ social structure and gene flow. “Our findings highlight the importance of considering animals’ behavioral responses when weighing the net benefit of conservation interventions,” she adds.

Co-author and ecologist Rickert van der Westhuizen of the South African provincial conservation body Ezemvelo KZN Wildife , says such findings could see some management practices change. Rhino horns on average grow back within 18 months.

"There will always be a trade-off between benefits and costs. This study, and others, show that the effects of dehorning are not severe enough to stop doing it. As long as such operations do not result in the loss of rhinos or lead to a decrease in population productivity, it is worth every cent," he believes.

doi: https://doi.org/10.1038/d44148-023-00170-8

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As a medicine, study finds rhino horn useless — and potentially toxic

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• A new study has found that concentrations of essential minerals inside rhino horns are too low to provide consumers with any health benefits, questioning their use in traditional Chinese medicine.
• The scientists also revealed that rhino horns contained potentially toxic minerals; the lack of quality control testing and regulatory oversight makes it even more pressing to address the sales of rhino horn derivatives for consumption.
• Researchers say that efforts to reduce consumer demand for rhino horn products must run in parallel with protection.

Fancy a taste of your own toenails? That’s what vendors in Vietnam or China could say when offering powdered rhino horn. This coveted “trophy” is made up of keratin, the same structural protein as human nails and hair. And a new study in Scientific Reports finds it about as nutritious, despite claims to the contrary, underlining the scientific consensus that consuming rhino horn has no real health benefits.

In parts of Asia where traditional Chinese medicine is deeply rooted, people have been consuming rhino horn for millennia. Medical texts from the 16th century show that rhino horn has been touted as a cure for ailments ranging from fever and rheumatism to snakebites and even demonic possession.

“Rhino horns have a long history of being sold as part of TCM [Traditional Chinese Medicine] by doctors who … believe that rhino horns … will dispel heat and clear toxins from the body,” said study lead author Terri Roth, head of the Center for Conservation and Research of Endangered Wildlife (CREW) at Cincinnati Zoo & Botanical Garden in the U.S.

Yet the new research revealed that while beneficial minerals were present in rhino horn, they only occurred in very low concentrations — not enough to impart any kind of benefit.

The trade in rhino horn has long been the main threat to rhino populations in Africa and Asia, where poachers kill the animals and cut off their horns with a machete or chainsaw — sometimes while the animal is still alive. This makes understanding the components of rhino horn all the more important.

‘Implausible’ health benefits

To get at the heart of what rhino horn consumers are ingesting, the study’s authors quantified the minerals in shallow and core samples of horns from captive white ( Ceratotherium simum ) and black rhinos ( Diceros bicornis ), both native to sub-Saharan Africa. The white rhino is near-threatened, and the black rhino is critically endangered.

“The few reported studies on rhino horn’s medicinal properties focused primarily on antipyretic [fever-reducing] activity, and published results are contradictory,” the researchers write, warning of the recent expanded use of rhino horns to treat severe diseases for which medical care may be needed.

After examining the horn samples for various minerals like sodium, sulfur, copper and iron, the scientists found both essential and potentially toxic elements present. Of the 12 essential minerals they detected, concentrations were substantially lower than in a much cheaper daily vitamin. As such, the health benefits of eating rhino horn appear “implausible,” their study reads.

Toxic minerals, too, were found in such low concentrations that they likely wouldn’t pose a major human health risk at typical doses. But there’s a caveat.

Roth’s team found that samples harvested from the exterior surface of the horn contained higher concentrations of many potentially toxic minerals and metals, in line with the levels found in the rhino’s environment — particularly in the soil. Soil composition varies greatly from one location to another, making it hard to predict the components that adhere to rhino horns.

Roth cited arsenic as an example. In what she calls “clean” rhino horns, arsenic concentrations likely wouldn’t be harmful to human health. In soil-contaminated samples, however, they could exceed the levels allowed by regulators of human food and pharmaceuticals.

“You may be paying a lot of money for a sample containing dirt,” she said.

Wild rhino horns would contain even greater amounts of contaminated material than the captive ones used in the study, pointed out Olivia Smith, communications manager at U.K.-based NGO Helping Rhinos. And given its current illegality, there’s no quality control testing or regulatory oversight of horn-based products, making consuming rhino horn a perilous bet.

“Any medicine, either botanical, mineral or animal products, if used improperly, could cause harm to our patients,” commented Lixing Lao, the president of Virginia University of Integrative Medicine and co-chair of the Coalition of Wildlife Protection in TCM.

“The contribution of this study brings us awareness about this product,” he added. “For consumers who have no knowledge of Chinese medicine, it could pose more risks and be harmful if they take these products by themselves.”

From status symbol to ‘handful of dirt’

Demand for rhino horn is driven nearly exclusively by Asian countries, predominantly Vietnam and China, where demand fuels poaching on the other side of the globe or, as Lao summed it up: “Endangered animal issue is a global problem. If an extinction of animals happened in one place, it would affect the other part of the world.”

In 2022, the number of rhinos across Africa increased by 5.2% to 23,290, but poachers slaughtered at least 561 African rhinos, including 448 in South Africa alone. The country, home to more rhinos than any other, saw the poaching figure rise to 499 in 2023.

“Currently, all international media blame TCM as the one that’s responsible for the extinction of endangered animals in the world,” Lao said, flagging potential reputational damage “if the TCM community does not act to protect the endangered animals.”

Globally, the persistent decimation of rhinos has led to the extinction of multiple subspecies. Today, the northern white rhino ( Ceratotherium simum cottoni ) is functionally extinct, with just two females left. Both the Javan and the Sumatran rhinos are listed as critically endangered, with likely little more than 50 individuals left each. Recently, investigators in Indonesia arrested poachers accused of killing around a third of the world’s Javan rhinos. The biggest threat to the Indian rhinoceros  (Rhinoceros unicornis ), currently listed as vulnerable, is also poaching for its horn.

For Smith, Africa’s rhino statistics “certainly are a mixed bag.” But unlike for the Javan and Sumatran rhinos, she’s optimistic that with international support, “the African rhino species have a sustainable future in their natural habitats.”

Dave Balfour and Sam Ferreira, respectively the chair and the scientific officer of the African Rhino Specialist Group at the IUCN, the global wildlife conservation authority, told Mongabay in an email that even though poaching persists, the future of African rhinos looks more upbeat.

“Fortunately, rhinos breed well in Africa if given the chance,” Roth said. “However, it is not yet time to let down our guard in Africa or Asia.”

“Sadly, there are buyers who are now … banking on the extinction of the species so that they may capitalize” — the rarer the animal becomes, the more value its horns hold, Smith explained. “To combat this will take an entirely different approach, in which all commercial value must be removed from the horn.”

Increasingly, wealthy consumers are buying rhino horns not as a fever medicine, but as a mythical detoxifier for an excessive lifestyle, or as a status symbol, making their consumption “totally disconnected from the desire to treat illness,” Roth said.

On the other hand, “if the gift of rhino horn is equated with a handful of dirt, perhaps people will find something more suitable when trying to please or impress someone else,” she added.

Reducing consumer demand to reduce poaching

Conservationists have deployed many creative initiatives to deter rhino poaching. Researchers in South Africa have recently injected radioactive material into rhino horns, so they can be picked up by radiation detectors at international border crossings.

Dehorning is another solution, where a rhino is regularly tranquilized and its horn cut off to make it less valuable as a poaching target. But even this doesn’t guarantee immunity to poaching. Besides, rhinos need their horns to assert dominance, defend themselves, steer their calves and forage in compact soils for hidden grasses.

According to Roth, it’s best to have many actions in play, given that the wildlife conservation landscape is changing constantly.

“Protecting wild rhinos from poachers is an absolute priority, but in so doing, we are only treating the symptoms of the problem,” she said.

Some organizations have therefore made tackling consumer demand for horns a priority, but it’s a strategy for the long haul.

“Changing long-held traditional beliefs takes years, sometimes generations, so while these longer-term efforts are put into action, it is vital we maintain anti-poaching efforts to buy the rhino enough time for demand reduction strategies to take effect,” Smith pointed out. “Without the immediate work being done to protect rhinos, there would be none left by the time demand reduction programs saw results. And alternatively, without the long-term goal of ending the demand, we will be stuck in a never-ending loop of intensive, and expensive, rhino protection.”

Smith said that she wishes more people would make the link between the live rhinos grazing peacefully in the wild and the horn powder, but added that it isn’t realistic.

“As long as the use of rhino horn is legitimized by governments within countries that have the highest demand for rhino horn, not only will there be cracks in the market for poached horn to slip through, but the power of messaging around not using horns will be diluted,” Smith pointed out.

Roth explained that she hopes her study will make people think twice about rhino horn consumption, but added that she’s “not naive enough” to think that scientific results will substantially sway public opinion. “In today’s world, people choose to believe science that supports what they want to do while disregarding that which doesn’t.”

Still, if there’s a chance that the absence of health benefits overturns even just a few people’s beliefs, scientists know that they ought to share it.

Banner image: Targeting demand for rhino horn-based products must complement efforts to protect rhinos from poaching. Image by Geranimo via Unsplash .

Roth, T. L., Rebolloso, S. L., Donelan, E. M., Rispoli, L. A., & Buchweitz, J. P. (2024). Rhinoceros horn mineral and metal concentrations vary by sample location, depth, and color.  Scientific Reports ,  14 (1). doi: 10.1038/s41598-024-64472-z.

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The Sixth Rhino: A Taxonomic Re-Assessment of the Critically Endangered Northern White Rhinoceros

Colin p. groves.

1 School of Archaeology & Anthropology, Australian National University, Canberra, Australian Capital Territory, Australia

Prithiviraj Fernando

2 Centre for Conservation and Research, Rajagiriya, Sri Lanka

Jan Robovský

3 Department of Zoology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic

Conceived and designed the experiments: PF CPG. Performed the experiments: PF. Analyzed the data: PF CPG JR. Contributed reagents/materials/analysis tools: PF JR. Wrote the paper: PF CPG JR.

The two forms of white rhinoceros; northern and southern, have had contrasting conservation histories. The Northern form, once fairly numerous is now critically endangered, while the southern form has recovered from a few individuals to a population of a few thousand. Since their last taxonomic assessment over three decades ago, new material and analytical techniques have become available, necessitating a review of available information and re-assessment of the taxonomy.

Dental morphology and cranial anatomy clearly diagnosed the southern and northern forms. The differentiation was well supported by dental metrics, cranial growth and craniometry, and corresponded with differences in post-cranial skeleton, external measurements and external features. No distinctive differences were found in the limited descriptions of their behavior and ecology. Fossil history indicated the antiquity of the genus, dating back at least to early Pliocene and evolution into a number of diagnosable forms. The fossil skulls examined fell outside the two extant forms in the craniometric analysis. Genetic divergence between the two forms was consistent across both nuclear and mitochondrial genomes, and indicated a separation of over a million years.

Conclusions

On re-assessing the taxonomy of the two forms we find them to be morphologically and genetically distinct, warranting the recognition of the taxa formerly designated as subspecies; Ceratotherium simum simum the southern form and Ceratotherium simum cottoni the northern form, as two distinct species Ceratotherium simum and Ceratotherium cottoni respectively. The recognition of the northern form as a distinct species has profound implications for its conservation.

Introduction

As much a cause for celebration the conservation success of the Southern white rhino is, equally shocking and dire is the fate of the Northern white rhino. After recovering from a handful of survivors at the turn of the 20 th century, the Southern form escaped relatively unscathed from the large-scale African rhino poaching epidemic of the 1980s. In contrast, the once tolerably numerous Northern form has been reduced to a tiny remnant (less than 20) in the Garamba National Park, Democratic Republic of Congo, and a similar number in two zoos. Teetering on the brink of extinction, its in-situ and ex-situ survival hang by a thread. Urgent and concerted effort is required to stave off its extinction. The taxonomic status of the Northern form is central to determining its conservation importance and will be a critical driver of efforts to save it.

In the thirty years since the last taxonomic revision of the White Rhinoceros, genus Ceratotherium [1] , new material and analytical tools have become available, necessitating a reassessment of the taxon. The metrical data of Groves [1] , and some collected subsequently, can be re-analysed using sophisticated statistical packages that have become more readily available. Detailed information and measurements have been published on a remarkable Early Pleistocene skull KNM-ER 328C [2] ; this had earlier been reported briefly by Hooijer [3] . Further material and analysis has been published by Guérin [4] – [7] . The external phenotypic differences between Northern and Southern forms of White Rhino tentatively raised by Groves [8] have been extended and supplemented by Hillman-Smith and colleagues [9] , [10] . The reality of these distinctions needs to be examined.

Genetics has become an important criterion in establishing taxonomic identity. The chromosomes of northern and southern white rhinos apparently do not differ consistently; the typical diploid number is 82, but a northern male had 2n = 81 (heterozygous for a Robertsonian translocation) as did his two female offspring [11] . Merenlender et al. [12] found electrophoretic variation on 25 allozyme loci between northern and southern white rhinos to be unexpectedly low: Nei's distance was 0.005, compared with a distance of 0.32 between Ceratotherium and Diceros . Estimates of heterozygosity were low for all rhino taxa examined in their study and less than 0.1% of loci were polymorphic in any of the three taxa. Stratil et al. [13] studied some of the same individuals of northern white rhinos and found much greater protein polymorphism, which they attributed to the use of more sophisticated and sensitive methods. George et al. [14] found a fixed difference in serum esterase between the two white rhino taxa – ES3 being present in all southern white rhinos (n = 23), but in none of the northern (n = 7). George et al. [15] , using restriction enzyme analysis of mtDNA on a single individual of each white rhino subspecies, found 4% difference, compared to about 7% between white and black rhinos. A subsequent study by some of the same authors, with a higher sample of individuals and additional restriction enzymes, estimated the mtDNA divergence between the two white rhinos at 1.4%, and the inter-generic divergence at 4.5% [14] . Morales and Melnick [16] , based on restriction enzyme analysis of a 1.6 kb mitochondrial ribosomal gene segment, found 0.3% sequence divergence between the white rhinos, and 1.8–2.1% between white and black rhinos. Thus, previous genetic analyses have provided conflicting results on the divergence between the two white rhino taxa.

Here we report on a reassessment of the taxonomic status of the white rhinos based on new material and reanalysis of existing data, and review ancillary information on the taxa.

In all skulls of Ceratotherium simum simum examined, the protoloph on the molars and the posterior premolar, sweeps backward from about one third of its length, so that it runs more distally than lingually for the remaining two thirds. In all C. s. cottoni , about one half or more of the protoloph is distolingual in direction.

In the southern form, the ectoloph on the third molar is produced back more behind the metaloph, to form a larger metastyle.

Dental Metrics

Measurements of mean crown heights taken by CPG in skulls of southern white rhinos varied in both M1 and M2 from 45 to 72 (n = 4 for both teeth), and in northern skulls the range was 35–52 (n = 10 M1, n = 7 M2).

Cranial Anatomy

The palate ends approximately level with the junction of the second and third molars in the southern form, and halfway along the second molar in the northern.

The incisive foramen ends level with about three quarters of the way along the second premolar in the southern form, and level with the anterior edge of, or one quarter of the way along, the second premolar in the northern.

Cranial Growth

Figure 1 depicts skull growth in males; Figure 2 in females. Basal skull length appears not to increase after stage 3 in males of cottoni ( Figure 1a ); there are no stage 3 skulls of females for cottoni , but certainly there is no difference between stages 4 and 5 ( Figure 2a ). There appears, on the other hand, to be some marginal increase in growth after stage 3 in both sexes of simum ( Figures 1a , ​ ,2a). 2a ). By contrast, in occipitonasal length, males of stage 3 are by no means full-sized in either taxon ( Figure 1b ), nor is one of the two available females of simum ( Figure 2b ).

Age stages are as follows: Stage 2, first molar in process or erupting; 3, second molar in process of erupting, second and third premolars in process of replacement; 4, second molar in wear; fourth premolar in process of replacement; 5, third molar in process of eruption; 6, third molar in occlusion.

Age stages as in Figure 1 .

Nasal breadth ( Figures 1c , ​ ,2c) 2c ) continues to grow noticeably between stages 3 and 4. In stage 3, the nasal boss of simum is narrower than that of cottoni , but the difference has disappeared by maturity. Even by stage 3, the male already has a wider nasal boss than the female, and the single stage 2 skull of male cottoni has wider nasals than the two corresponding stage females.

The depth of the dorsal concavity appears not to change with age in cottoni or in males of simum ( Figures 1d , ​ ,2d), 2d ), but the limited evidence suggests that the depth may decrease somewhat between stages 3 and 5 in simum females ( Figure 2d ).

Because there is no evidence for any difference between stages 4 and 5 in nasal boss breadth, these two stages have been combined in Figure 3 . In the two living taxa, the values for the two sexes of cottoni just overlap, while those for simum (smaller sample) do not. This character can therefore be used with nearly complete confidence to allocate skulls whose sex is unknown. Nasal breadth measurements are available for the North African Arambourg skull and for the skull from Ileret. If these are comparable to modern white rhinos, the Arambourg skull will be a female, the Ileret skull probably a male.

Cranial Metrics

Univariate comparisons between fully grown samples of living white rhinos are shown in Figure 4 , and comparisons with fossil specimens in Figure 5 .

Figure 4a shows the depth of the dorsal concavity in adults and 4b, maxillary toothrow length.

Figure 5 continues the comparisons between the two living taxa, and extends them to those individual fossil specimens which are complete enough to take the measurements concerned. Figure 5a shows the basal lengths of living and fossil white rhinos and Figure 5b occipitonasal lengths. Occipital breadth is shown in Figure 5c and Occipital height in Figure 5d . Figures 5e and 5f ; depict depth of dorsal concavity and maxillary toothrow length, respectively. Figure 6 represents bivariate scatterplots for some of the skull measurements: occipitonasal length relative to basal length, occipital height relative to occipital crest breadth, and dorsal concavity relative to occipitonasal length. Insepction of actual skulls demonstrates that the difference in the depth of the dorsal concavity is easily detected visually.

Figure 7 is a scatterplot of the first two Functions of a Discriminant Analysis using 7 cranial variables: Occipitonasal length, Basal length, Zygomatic breadth, Occipital breadth, Occipital height, Nasal breadth and Dorsal concavity depth. Four groups were entered: southern males and females, and northern males and females; the Arambourg and Ileret fossils were entered as unknowns, meaning that they will be allocated to a position in the dispersion calculated on the basis of the four groups, but do not have a chance to extend the dispersion on their own account.

Ungrouped fossil specimens, with their DF values, are: Ileret (3.12, 2.28), with simum males; Arambourg (2.59, −2.81), with simum females. DF1 accounts for 68.4% of total variance, DF2 for 31.1%.

Postcranial Skeleton

The crural index (tibia expressed as a percentage of femur length) measured 71–72% in three southern and 73–75% in three Northern rhino specimens.

External Measurements

The heights of two Southern males at Zoo Usti nad Labem, Czech Republic, measured 168 and 165 cm; a female, 157 cm. All three were born in Umfolosi, 1966–1970. The height of a Northern female at Dvur Kralove (Najin) was 157 cm. Spine length of a Northern female (Najin) was 269 cm, of a male (Suni) was 271 cm; and that of a hybrid × Southern female (Nasi) was 269 cm.

The number of bps used for analysis from each fragment is given in Table 1 . Analyzed segments showed consistent divergence between the two forms. No nucleotide polymorphisms were observed within C. s. simum or black rhino subspecies D. b. minor and D. b. michaeli in the analyzed mitochondrial 12S and NADH segments, or in the nuclear Amelogenin segment. The mitochondrial D-loop segment showed polymorphism within the two black rhino subspecies but not within C. s. simum . Divergences observed between the taxa in respect of each analysed segment are given in Table 1 .

We found differences that were diagnostic of the two taxa in practically all characters examined.

The two forms of white rhino showed distinctive dental morphology. The protoloph on all molars and the posterior pre-molar in the southern form was oriented parallel to the toothrow in the distal two thirds, whereas it was diagonal for one half or more in the northern form. Additionally, the ectoloph on the third molar was produced back more behind the metaloph, forming a larger metastyle in the southern form. Therefore, dental morphology clearly distinguishes simum from cottoni .

Guérin [5] suggested that the teeth are larger in southern white rhinos, especially (in the upper toothrow) P4, M1 and M2.

The index of hypsodonty is defined as:

Guérin [5] gave hypsodonty values for two specimens of P4 in white rhinos as 188.68 and 201.96, contrasting with black rhinos at 134.65 and 142.20. For M3 he gave 136.76 in a white rhino, compared to 121.15 and 102.36 in two black rhinos. His white rhino indices would correspond to crown heights in the white rhinos of about 85 mm for M3, and 95 and 101 mm for P4. These compare well with the figures for M1 given by Hillman-Smith et al. [9] for southern whites of 88 at the time of eruption, rising to 97 at the time of the eruption of M2, and falling again thereafter as wear proceeds.

As remarked by Hillman-Smith et al. [9] , true crown heights are difficult to measure on teeth still in place in the jaw, and crown height above the alveolar line is much easier to measure (if less anatomically exact), although because of continuing eruption the height remains constant for longer. Mean crown heights taken in this fashion on M1 remain at about 43–47 mm until quite an advanced stage of wear [9: Table IV]. Measurements taken by us indicate greater crown height in M1 and M2 in simum compared to cottoni , consistent with the presence of lower-crowned cheekteeth in northern white rhinos. The cheekteeth are thus lower-crowned as well as being somewhat smaller (see above).

Differences in the morphology of the palate and the location of the incisive foramina showed diagnostic differences between the two forms. The palate was longer and the incisive foramen located more posteriorly in the southern form, than in the northern.

A number of variations in cranial growth between the two forms were noted. The differences in the basal length and occipitonasal lengths of different stage skulls suggested the elongation of the occipital crest after stage 3 in both forms, but the differential growth of the occipital crest was greater in the northern form due to the earlier cessation of basal growth in cottoni . Although some differences in nasal breadth, suggesting a similar pattern to occipitonasal growth, were noted, the small sample sizes precluded identifying any fixed variation between the two forms.

The most striking sexual dimorphism, in a character nearly independent of body size, was shown by the width of the nasal boss. The difference between the sexes in this character was evident in both forms with the width usually being greater in males. This sexual dimorphism was accentuated in the case of the southern form with no overlap of measurements between the sexes.

Heller [17] concluded that northern and southern white rhinos differed by the depth of the dorsal concavity and by the length of the toothrow, and Groves [1] concurred. Our findings show that there is a striking difference between the two taxa: the depth is much greater in southern white rhinos, and the dorsal outline of the skull is very flat in northern. There is no overlap in males, but a slight overlap in females. In females the dorsal concavity appears to become slightly flatter with age, but not in males. Thus, Heller's claim of differences in dorsal concavity is borne out by our findings. Heller's [17] finding is vindicated for the maxillary toothrow as well (see above), although in this case there are overlaps in both sexes. There is no difference between the sexes in cottoni (the mean for females is somewhat larger than that for males, although within the quartile range), but females of the southern form do have a shorter toothrow than males.

Guérin [5: pp. 171–172] found that the skulls of the southern form were very slightly larger but the orbitotemporal fossa was longer, and, according to the text (p.171) that the occiput is wider in the northern, but his Table 42 (p.172) shows this to be the opposite (Guérin's measurement 16). Guérin also found the mandible of the southern white rhino was larger, with a longer symphysis; and the corpus and condyle higher. We can test the claim of a size difference and of a difference in the occipital crest, but we did not take any measurements of the mandible.

In comparing basal lengths, we found little or no difference between the two living taxa, but the basal lengths of the fossils from Ileret and Olduvai Bed IV were much greater than any living representative, and that of the Arambourg skull, which we suggested was female, was greater than any living female. The broad outlines were similar for Occipitonasal length, but with differences. The first difference was that one specimen from South Africa was considerably longer in occipitonasal length than any other, that is to say, it had an occipital crest that is posteriorly extended. The second difference was that the occipitonasal lengths of the Arambourg and Ileret skulls were not longer than modern females and males respectively, implying that the occiput was less posteriorly extended than in modern white rhinos.

We found that the occipital breadth was strongly sexually dimorphic, second only to nasal breadth, but in contrast to nasal breadth, the dimorphism in cottoni was greater. Between the northern and southern forms, occipital breadth measurements of males overlapped considerably, but those of females only very slightly, northern being much smaller than southern. So in this sense Guérin's findings are vindicated. All of the fossils that could be measured had an extremely broad occiput (if their sexes were correctly interpreted: see results). Thus it is clear that sexual dimorphism existed in the early Pleistocene, the Ileret skull having a broader occiput than modern males, the Arambourg skull broader than modern females. The occiput of the Olduvai Bed II specimen could be measured, and it was very broad like the Ileret specimen.

Occipital height was likewise highly sexually dimorphic, in this case more in the southern form than in the northern. In comparing the two forms, male southern skulls were almost absolutely larger in this measurement than male northern skulls. The measurement of the Arambourg skull was less than in any living specimen, while that of the Ileret skull was within the range of modern females; this supports the conclusion from occipitonasal length, that the occiput is less posteriorly extended (i.e. the occipital crest is shorter) in the fossil than in living specimens. The Olduvai Bed II specimen is somewhat larger in this measurement than the Ileret skull; the Kibish specimen is larger still, within the range of male southern skulls.

Of the two features used by Heller [17] to distinguish the two modern taxa, Arambourg and Ileret both have a relatively deep dorsal concavity like modern southern skulls ( Figure 5e ); the toothrow of the Arambourg skull is (assuming it is a female) longer than would be expected for a modern southern specimen, while that of the Garusi specimen is as long as would be expected were it a male of the same population ( Figure 5f ; the toothrow length of the Ileret skull is unavailable).

In bivariate analysis of skull measurements, some of the characters clearly separated the two extant taxa while others did not. The positioning of the fossil specimens was variable. In the occipitonasal length against basal length, there was as expected no difference between the two modern forms. The Olduvai Bed IV specimen, though it was very much bigger than any modern specimen, was modern in its proportions, the Arambourg skull was on the edge of modern proportions, while the Ileret skull was outside the modern range.

Occipital breadth to height comparisons confirmed the shorter occipital crest of the Arambourg and Ileret skulls, but the Olduvai Bed II specimen was within the modern range. When dorsal concavity depth was plotted against occipitonasal length (see above), the difference between the two modern taxa was striking, and there was no overlap although they come close; the Arambourg and Ileret skulls came just within the southern range.

In the discriminant function analysis using seven variables ( Figure 7 ), the first Function (horizontal), which accounted for 68.4% of the total variance, was heavily weighted positively on dorsal concavity depth and, less heavily, on occipital breadth and occipitonasal length, and fairly strongly weighted negatively on nasal breadth and less strongly on occipital height ( Table 2 ). The second Function, which accounted for 31.1%, was fairly heavily weighted positively on occipital nasal length and occipital breadth, less heavily on nasal breadth, and weakly negatively weighted on zygomatic breadth. Southern and Northern groupings separated completely in the discriminant function analysis, but the sexes within each group overlapped somewhat. The Arambourg skull fell within the dispersion of southern females, the Ileret skull within the southern males. All skulls were closer to the centroids of their own geographic groupings, which was also true of the leave-one-out cross- validations ( Table 3 ). While a few males within each geographic sample could be misidentified as females, and vice versa, there was no misallocation of northern as southern or vice versa.

Guérin [5] found that the metapodials are a little bigger in simum , but his data show that in effect it is the medial ones that are slightly longer, the laterals being somewhat shorter. Of several measurements taken by CPG on postcranial bones, a difference appears only in the crural index, suggesting slightly longer limbs in cottoni .

Hillman-Smith et al. [9] reported that full body size and sexual maturity in females are achieved at 6–8 years, but in males not until 10–15 years. They reported that adult males of southern white rhinos weigh 2000–2400 kg, and a subadult male, with the last molar not fully erupted, was already 2130 kg, and adult females weigh 1500–1700 kg. On the other hand, at 10–10½ years two northern males weighed only 1400 and 1600 kg and, at about the same age (9–10½ years), four northern females weighed 1400–1500 kg. Spine length (occiput to base of tail) was 259–284 cm in male and 248–273 cm in female southern white rhinos, and 266 cm in a northern adult (10-year-old) male and 245–262 cm in four northern females. To these may be added our measurements of 271 and 269 cm in a male and a female respectively, of the Northern form, just slightly larger than in Hillman-Smith et al.'s sample (the male, Suni, was also measured by Hillman Smith et al. [9] , but when only three years of age). Shoulder height in two southern males Hillman-Smith et al.'s sample was 174–178 cm, and in two 10-year old northerns, 151–152 cm (virtually the same as in four 9–14-year-old females, 150–154 cm). Northern white rhinos, these authors remarked, ‘appear to be shorter and smaller’. Our own shoulder height data (Southern male 168 cm, females 157 and 165 cm; Northern female 157 cm) are comparable, though again, most of them are on the large side.

Other measurements of southern white rhinos exist. Kirby [18] gave the measurements of a male and a female, stated to be ‘large’, as 179 and 177 cm respectively. Hitchins (personal communication in [9] ) gave two males as 178 and 174 cm.

Perhaps the largest series of body measurements in the literature for both forms is that of Heller [17] . (The figures are given in feet and inches, and have been recalculated as centimeters here). The height of a northern male is given as 166 cm, and of five southern males, of which four were mounted skins and one a mounted skeleton, is 148–188 cm; of the four mounted skins, the smallest, from the Leiden Museum, has no associated skull or skeleton so that its maturity cannot be guaranteed (and its proportions seem peculiar compared to the others), and the next smallest is 175.3 cm. The height of a northern female is given as 160 cm; that of a southern female is 155.6 cm. Heller's length measurements are head-and-body, so not comparable to those of Hillman-Smith et al. [9] .

Putting all these figures together, we get following body measurements:

Height [cm]

• Southern males 165–188 (n = 11), southern females 155.6–185 (n = 8)
• Northern males 151–165.7 (n = 3), northern females 150–160 (n = 6)

Length [cm]

• Southern males 259–284 (n = 10), southern females 248–273 (n = 4)
• Northern males 266–271 (n = 2), northern females 245–269 (n = 6)

Meagre as they are, these figures tend to substantiate the observation of Hillman-Smith et al. [9] that northern white rhinos are smaller – very markedly in the case of males, only slightly in the case of females. The spine length data are even more meagre, but appear to corroborate the height data. The weight discrepancies, however, are even greater for males than those for females about equivalent height.

It is possible to calculate height:length ratios from Heller [17] . For his northern sample, measured in the field, the range is 40.5–51.1% (n = 6); these are mostly immature, but the solitary value for an adult female falls squarely in the middle of the range. For an adult male, measured on a skeleton, we calculate 56.5%. For his southern sample, three males measured on mounted skins vary from 46.8–53.4%, one measured on a skeleton is 56.5%, and a female measured on a skeleton is 53.7%; the peculiar male, mentioned above, is only 41.9% (this specimen is of uncertain history and provenance; Jentink, [19] , records only that it was brought to the Netherlands, date unstated, on the ship ‘Mauritius’ and presented by the Minister of Internal Affairs in 1879).

We attempted to measure height/body length proportions from photographs, but these are rather subjective. Impressionistically, and in agreement with Groves [1] , we do tend to agree with Hillman-Smith [10] that northern white rhinos seem to stand higher in the leg than southern, which seem longer-bodied.

Other External Features

On the basis of published photographs [20] – [27] , and of observations and photographs by CPG of northern white rhinos in London, Antwerp, Dvur Kralove (also by JR) and San Diego, and of southern white rhinos in many institutions, there appear to be a number of consistent external differences between the two (See Figures 8 , ​ ,9). 9 ). Mostly, they concern the degree of skin folding and wrinkling, which deepens with age, and tends to be more marked in females than in males.

Left, Dan, male aged 40 years. Right, Zamba, female aged 37 years. Both, Usti nad Labem. Photos, Jan Robovsky.

Left, Suni, male aged 27 years. Right, Nabire, female aged 24 years. Both, Dvur Kralove. Photos, Jan Robovsky.

Costal grooving: no white rhino has the deep grooves, which correspond externally to the spaces between the ribs, which tend to characterise most black rhinos ( Diceros bicornis ). Some grooving nonetheless occurs in southern white rhinos, weak but becoming more accentuated with age, especially posteriorly, beginning about 2–3 ribs in front of the stifle fold. There is on the contrary little trace of costal grooving in northern white rhinos.

Fold over base of foreleg: if the animal is standing square, this fold always tends to be complete in southern white rhinos, but in northern it is usually less complete, not extending back to the elbow. This difference is not absolute.

Fold behind elbow: this is deep, fading upward toward the dorsal line, in southern white rhinos, but is hardly expressed in most northern ones.

Wrinkling around eye: southern white rhinos have deep circular wrinkles around the eye, but these are weak at the most in northern.

The dorsal profile is straighter in northern white rhinos, more concave behind the shoulder in southern.

The difference in the dorsal profile of the skull is readily appreciable on living animals.

Cave & Allbrook [28] could find no evidence of body hair in a subadult northern white rhino, whereas in southern white rhinos hairs were detectable by touch according to Alexander & Player [29] . The keepers at Dvur Kralove and Usti and Labem are of the opinion that this probably was a difference, although in southern whites they may become undetectable under insistent abrasion; and JR found no hairs on the flanks in three northern individuals (Saut [wild-born, died 2006], Najin and Suni [captive-born, still living]). CPG could detect no trace of body hairs by running a hand over the flanks of a docile northern white at San Diego Wildlife Park; hair was clearly detected by JR on the flanks of hybrid female Nasi, who died in 2007 in Dvur Kralove. This individual was bred under the same captive conditions as Saut, Najin and Suni and was older than Najin and Suni (if anything, hair would be expected to fall out, or at least abrade, with age). Note that hair is always to be found on the tail, muzzle at the base of the nasal horn, and ear rims, and (few, sparse) on the belly, throat, distal parts of both limbs, and apex of hump of both whites.

The keepers at Dvur Kralove Zoo are of the opinion that Northern white rhinos possess more shaggy ears and tail [30] . Several of the Northern white rhinos in Dvur Kralove Zoo are heavily shaggy on the ear rims (but some are not). We tend to consider these characters, based on observation of the many individuals of white and black rhinos in captivity, and wild as too variable for being diagnostic.

Fig. 8 depicts a male and female Southern White rhino; Fig. 9 , a male and female Northern White rhino, but from zoos in the Czech republic. The horns have grown abnormally as a consequence of years of captivity.

The Living Taxa: Behaviour and Ecology

Spassov [31] argued that the nuchal hump of the white rhinoceros serves the same function as the double horn: to enhance lateral visual display. The second horn duplicates the display function of the first horn, and the nuchal hump, which becomes apparent only in the head-up posture of lateral display, gives the impression of increased body size. One may take this further. In Diceros bicornis , the back is concave, leaving the withers and the croup as high points, whereas in Ceratotherium , both high points are duplicated, the withers by the nuchal hump, and the croup by the presacral eminence. The stimulus effect of the display is thereby increased.

The (former) distribution of the southern white rhino corresponded mostly to the Bushveldt Zone [32] . Northern white rhinos were said to live in open Combretum forest and nearby plains. According to Schomber [33] , population densities in Umfolosi are notably higher than elsewhere in the range, and southern populations always seem to have existed at higher density than northern.

The social organisation of the southern white rhino was described in detail by Owen-Smith [18] . There are two types of mature males: territorial (or alpha) males, and non-territorial (or beta) males who do not reproduce and whose presence in an alpha male's territory is tolerated. Rachlow et al. [34] found that territorial males are on average older than non-territorial males, and though the same linear size (as measured by body length), are markedly larger in chest girth and neck girth. Only territorial males scent-mark by spray-urination and by scattering their faeces, kick with the hind legs before and after defecation, and beat the horns against bushes. They have much higher testosterone levels, and they consort much more with females of high reproductive value (non-pregnant females without calves less than 10 months old).

In a very small population of northern whites introduced to Murchison Falls National Park, van Gyseghem [27] recorded the same dominance behaviours displayed by the sole adult male: spray-urination, hindleg kicking, horn beating and displays towards subadult males. The home ranges of all the individuals of white rhinos in Murchison Falls National Park were found to be 5 to 10 times larger than those found in the southern subspecies in Hluhluwe Game Reserve [27] .

At the “African rhino workshop, Cincinnati, October 1987” a discussion took place on possible behavioural/ecological differences between Northern and Southern white rhinos. It was reported that N. Owen-Smith noted that Southern white rhinos feed on short, nutritious grasses; given that the Northern white rhinos live in a wetter habitat, with long fibrous grasses, their feeding ecology could well differ, and K. Hillman-Smith concurred, but no research in Garamba had been conducted; her own casual observation indicated that Northern white rhinos “may eat more dicotyledons, and they have to survive in tall grasses such as Hyparrhenia and Loudetia in the wet season, and in burnt areas during the dry season. The social behaviour appears similar to that of the southern rhinos although ranges are about 10 times larger; which may be due to the very low population density in Garamba” [35] .

The basic reproductive parameters (gestation, first oestrus, first copulation, mean oestrous cycle, receptivity), sperm morphology and social behaviour of Northern whites in captivity is similar or identical to Southern whites [36] – [39] .

Policht et al. [40] confirmed that the repertoire of white rhino calls is much larger than that reported in other rhino species and also found an apparent similarity (large overlap) between acoustic parameters of homologous calls recorded in both forms of white rhinos.

Mikulica [36] observed a threat gesture involving swinging the head in Southern whites (in three individuals out of five), but not in Northern whites (six individuals). The behaviour was not noted by Backhaus [41] in Northern whites in the wild, but was detected in the captive population of Northern whites by Kuneš & Bičík [42] and Cinkova [43] , but the latter did not observe it in Southern whites. This emphasises that rare behaviours may not be detected even with long observation periods (I. Cinkova, pers. comm., observed this behaviour only twice in 323 h of observation).

The single known hybrid between Northern and Southern white rhinos was Nasi, born 1977, and euthanasied in 2007 because of cancer and accompanying severe pain. Nasi's health seemed poor considering her age; we are unsure whether to attach any significance to this, but five older individuals (pure-bred Northern) are still living, born in 1972, 1973 and 1974).

The diploid chromosome number appears polymorphic in Northern white rhinos, as noted above [11] . Sudan (Studbook no. 372) had a diploid number of 81, and this character was inherited by his two female offspring, Nabire (No. 0789) and Najin (0943).

In conclusion, the reported behavioural and ecological observations on the Northern and Southern whites do not provide a clear taxonomic distinction between the two forms. Importantly, nor do they contradict such a distinction.

Fossil white rhinos

Commonly, it has been assumed that, of the two African genera of rhinoceros, Diceros , with its browsing adaptations, is the more primitive, and can be traced back nearly unchanged to the Early Pliocene, for example at Laetoli, while the grazing Ceratotherium went through several evolutionary stages from the Early and Middle Pliocene C. praecox via the Late Pliocene/Early Pleistocene C. simum germanoafricanum to the modern white rhino [3] – [7] . Geraads [44] argued that it is in fact Diceros that has more derived skull shape, considering that the depth of the dorsal concavity increases during growth and the angle between the plane of the palate and the nuchal plane decreases in early ontogeny: the skull, in other words, becomes less like Ceratotherium with age. He transferred C. praecox to Diceros , and referred all the early stages of white rhinoceros to a species Ceratotherium mauritanicum , described from the Middle Pleistocene of North Africa (and surviving in North Africa until the Late Pleistocene, though replaced by C. simum in East Africa in the Early Pleistocene). The presumed stem species, from the Late Miocene of Greece and Iran, generally known as Diceros neumayri , he transferred to Ceratotherium , finding that though it was intermediate in cranial morphology, there were some respects (elongate antorbital portion of skull; occiput narrow base compared to crest) in which it more resembled modern Ceratotherium , and was a mixed feeder. He placed the separation of the two modern lineages “soon after the Miocene-Pliocene boundary”: Diceros evolved towards a browsing specialization, with smaller size, more transverse lophs on cheekteeth, more concave dorsal profile, while Ceratotherium became larger, with more inclined lophs and flatter dorsal profile. Kingston & Harrison [45] , on the basis of stable isotope analysis of the teeth, attributed a mixed diet to rhinoceros from Laetoli (Middle Pliocene), which they referred to provisionally as Ceratotherium praecox (note that their reference to “modern Laetoli specimens” [45: pp. 288, 289] is an inadvertent error: the four modern specimens analysed for the paper — 1 from the Sudan, 1 from W. Madi in Uganda, 1 from Garamba in Zaire, and 1 from the Laikipia Plateau in Kenya — were inadvertently added to the sample of modern specimens of other large herbivores from Laetoli [John Kingston, personal communication to CPG]).

Ceratotherium mauritanicum , according to Geraads [44] , differed from modern white rhinos by the weak postorbital constriction and wide nuchal crest, as well as the slender metapodials. He referred fossils from Kanapoi, Hadar, Dikika, Koobi Fora (below the KBS Tuff) and Rawi to it, but specimens throughout the Olduvai sequence were referred to C. simum (of which germanoafricanum was considered to be a synonym). Groves [1] had found that the type skull of C. mauritanicum and the skull from Koobi Fora were both wide postorbitally, and the Rawi skull fragment, like the Koobi Fora skull, had very broad occipital crests (that of the C. mauritanicum type skull is crushed in this region); skulls from Olduvai (both Bed II and Bed IV) resembled modern white rhinos in both these respects, but had extremely long toothrows, by which they differed from any modern white rhino.

The observed genetic divergences across taxa were consistent with the different evolutionary rates of the analyzed fragments. As expected, the nuclear fragment showed much lower levels of divergence due to the lower evolutionary rate of nuclear coding regions relative to mtDNA. Different evolutionary rates of the mitochondrial segments, especially the faster evolution of the D-loop, may explain the discrepancies in divergence observed by restriction digestion analysis of mtDNA in previous studies. Saturation consequent to its high evolutionary rate makes the D-loop unsuitable for analysis at the level of genera. The mitochondrial 12s, ND and the nuclear Amelogenin X fragments provide more meaningful generic comparisons.

The relative divergence of the presumed subspecies of white rhino was approximately twice (1.84±0.17) that between the black rhino subspecies, and was remarkably constant across all four fragments analysed. Assuming similar rates of divergence between the taxa, this argues for a longer separation of the white rhino taxa than the two black rhino taxa analyzed.

The divergence between the white rhino taxa as a percentage of the inter-generic divergence observed in previous studies were: for allozymes 1.6% [12] , and for mtDNA 57% [15] , 31% [14] and 15.4% [16] . With an observed divergence of 15.8% and 18.6%, for the ND and 12S fragments respectively, our results correspond well with that of Morales and Melnick [16] . Allozymatic analysis is generally not sensitive enough for assessing divergence at the level of subspecies. The higher rates observed by George et al. [14] , [15] probably reflect a larger representation of the D-loop due to the particular restriction enzymes used. The divergence of 23.5% observed by us in respect of the Amelogenin fragment strongly supports the divergences observed in the 12S and ND segments. Due to the very low evolutionary rate of nuclear DNA, the estimate is based on only 1 and 2 mutations between the black rhino and white rhino taxa respectively, hence has lower resolving power than the mtDNA. Thus, we suggest 15–20% of the inter-generic divergence as a justifiable estimate of the divergence between the two white rhino taxa. The observed patterns of divergence and consistency of divergence ratios between taxa across analysed segments, justify the use of the estimated inter-generic divergence in assessing the divergence time of white rhino subspecies.

The Ceratotherium and Diceros divergence is dated to about 7 million years from the fossil record (Hooijer [3] , although only the Miocene-Pliocene boundary according to Geraads [44] ). The divergences observed by us in relation to the fossil evidence suggest a slower molecular clock in rhinos than in smaller mammals. Slow molecular clocks have been observed in elephants [46] and marine mammals [47] and maybe explained by the effects of longer generation time, increased body mass and lower metabolic rate on evolutionary rate [48] . Calibrating a molecular clock on the fossil evidence, the observed genetic divergence between the two white rhino taxa suggests their separation for at least 1–1.4 million years if Hooijer's [49] date for the separation of the two genera is correct, and 0.75–1 million years if Geraads' [44] date is more correct.

The living taxa: taxonomy

Northern and southern white rhinos have, without exception, been distinguished as subspecies within a single species, Ceratotherium simum . The northern form is universally distinguished as simply a subspecies, Ceratotherium simum cottoni (Lydekker, 1908), leaving the southern form as the nominotypical subspecies, C. s. simum (Burchell, 1821). We have, however, found that the two differ absolutely in numerous respects: the skull is readily distinguished ( Figure 10 ), the dentition is somewhat different ( Figure 11 ), they can be differentiated externally apparently without error, there is evidently a fixed difference in a serum enzyme and they are clearly distinguishable genetically in analysis of both mitochondrial and nuclear genomes. Under the Phylogenetic Species Concept (the only objective concept applicable to allopatric forms), we have no option but to consider them specifically distinct. While short separation times may characterise species pairs that are perfectly distinct by criteria of diagnosability and even reproductive isolation, a long time since separation does considerably strengthen other evidence for species status. Genetic analysis clearly indicates a separation time of over a million years between the two taxa, justifying their recognition as separate species: Ceratotherium simum (Burchell, 1821) and Ceratotherium cottoni (Lydekker, 1908).

Upper photo from Heller (1914, plate 17, fig. 3 ), lower photo by E. Trumler of skull in Zoologische Staatssammlung, Munich.

The northern white rhino is today on the verge of extinction. Its taxonomic distinctiveness argues strongly for its conservation, as its demise will mean the permanent loss of a unique taxon that is irreplaceable. The admirable success of the conservation histories of the Southern white rhino and the Indian rhino, both of which were brought back from the brink of extinction by successful conservation efforts, does, however, hold out hope that the northern white may yet be saved for posterity. With less than 20 individuals in the wild, the population cannot absorb any more poaching. It is very likely that any cause of increased mortality, of which poaching is the most threatening, and most easily addressed, will push them over the edge. Therefore, absolute protection from poaching is a must for the in-situ conservation of the species.

The highly successful management of white rhinos under semi-captive and captive conditions in Southern Africa indicates the importance of ex-situ conservation. Unlike in the case of the Javan rhino, where no captive population exists, and of the Sumatran rhino where captive breeding has only recently been achieved, and that only by a single female, the presence of a healthy if small captive population and their long history of successful management makes the ex-situ conservation of the northern white much more likely to be successful. For successful in-situ and ex-situ conservation of the northern white rhino, the lynch pin will be the availability of funding. In an age where billions of dollars are poured into saving companies going bankrupt and trillions into wars of arguable provenance, can we not spare a fraction of that to save a unique and charismatic megavertebrate and begin to address our disastrous impact on planet earth.

Morphometrics

CPG studied and measured skulls in the following collections (the abbreviations used here are in brackets following the names of the institutions): Natural History Museum, London (BM); Royal College of Surgeons, London (RCS); Powell Cotton Museum, Birchington (PC); Landesmuseum für Naturkunde, Karlsruhe (LNK); Zoologisches Institut, Hamburg (ZIH); Museum Royale de l'Afrique Centrale, Tervuren (MRAC); Naturalis, Leiden (RML); Naturhistoriska Riksmuseet, Stockholm (NRS); Muséum National d'Histoire Naturelle, Paris (NMP); American Museum of Natural History (AMNH); Smithsonian Institution (USNM).

The total number of skulls was 56 in all, the adult totals being as follows: Southern males 8, females 5; Northern males 18, females 14.

Fossil specimens are as follows (one specimen in each case): Tighenif (Ternifine), Algeria, latest Early Pleistocene or base of Middle Pleistocene, previously described by Arambourg [50] ; measurements of a skull from Ileret (Koobi Fora Formation), Lake Turkana, Kenya, base of Early Pleistocene, taken from Harris [2] ; Garusi, Tanzania, Middle Pliocene; Olduvai Bed II, Tanzania, Early Pleistocene; Olduvai Bed IV, Tanzania, early Middle Pleistocene; Kibish Formation (Omo River), Ethiopia, late Middle Pleistocene. Of these, only the first two (the Arambourg and Ileret skulls) are nearly complete; the others are fragmentary.

The following measurements were taken on each skull: Occipitonasal Length, Basal Length, Zygomatic Breadth, Occipital Breadth (occipital crest), Occipital Height (opisthion to opisthocranion), Nasal Breadth (nasal boss), Toothrow Length (P2 to M3), Depth of Dorsal Concavity (greatest distance from dorsal contour of cranium to a rod resting on nasal boss and occipital crest).

We entered measurements of skulls and teeth of white rhinos into a file in SPSS, version 12.0.1, and a made series of univariate and bivariate plots, and ran a series of discriminant analyses. Dental eruption stages follow a previous study [1] .

JR studied hair distribution and took some body measurements on three adults of Southern whites (one male, two females), two immobilized adults of Northern whites (one male, one female), one dead male Northern white (not measured) and one euthanized hybrid female. Some standard measurements [9] were not always available (e.g. for time limitation in immobilized individuals) and sometimes they were difficult to obtain accurately (especially if the individuals were lying down). This was carried out in accord with the laws and ethical guidelines (No. 2045/2004-1020) established in the Czech Republic. Body measurements were approved by representatives of the Dvur Kralove ZOO (owner of the animals). The immobilization of measured individuals was carried out by representatives of the Dvur Kralove ZOO (with veterinary assistance) during the course of attempted artificial inseminations in collaboration with representatives of the Leibniz Institute for ZOO and Wildlife Research (Berlin). The procedure was noninvasive and did not involve any increased stress to the rhinos or increase in duration of the immobilisation.

Samples for genetic analysis consisted of blood or tissue. Except for those downloaded from GenBank, these were taken during the course of routine veterinary analysis by approved veterinary authorities of San Diego zoo; in no case did their extraction involve any increased stress to the rhinos or increase in duration of the immobilisation. Details of samples are given in Table 4 . DNA extraction followed a phenol/chloroform extraction and QIAGEN column purification protocol. Primers and conditions for PCR amplification of 12S and D-loop mitochondrial fragments followed Fernando et al. [51] . The 12S primers amplified a 937 bp fragment of the mitochondrial 12S ribosomal RNA gene and the D-loop primers a 413 bp fragment incorporating 21 bp from the 3′ end of tRNA-Pro and 392 bp of the adjacent D-loop. Primers RH-ND-F, 5′-AAC AGT ACA ATT GAC TTC CAA 3′ and RH-ND-R, 5′ CCK GCG TTT AGT CGT TCT GTT 3′ for amplifying a mitochondrial NADH gene fragment were based on Indian rhino (Accession No. X97336) and white rhino (Accession No. NC001808) mtDNA sequences from GenBank. They amplified an approximately 1.2 kb fragment including part of tRNA-Glycine, NADH dehydrogenase subunit 3, tRNA-Arginine, NADH dehydrogenase subunit 4L and part of NADH dehydrogenase subunit 4. Primers Amel-3, 5′-GCA CCC TGG TTA TAT CAA CTT-3′ and Amel-6 5′-GGG TTC GTA ACC ATA GGA AG-3′ for amplification of the nuclear amelogenin (AMELX) gene were designed based on sequences from human, porcine and rat amelogenin (AMELX) genes. They amplified an approximately 1,685 bp fragment.

Amplifications were conducted in ABI 9700 PCR thermocyclers, using 1 µl DNA extract, 18 µl PCR buffer dNTP mix, 0.5 µl 10 µM each primer, 0.1 µl Taq DNA polymerase, and 14.8 µl water. Amplifications were preceded by a 93°C step of 3 minutes. Samples were amplified for 40 cycles by denaturing at 93°C, annealing at 50°C and 66°C respectively for ND and Amelogenin primer pairs respectively, and extension at 72°C; each segment lasting one minute. Amplifications were followed by an extension step of 72°C for 15 minutes. Amplification products were sequenced in forward and reverse directions with the PCR primers and internal sequencing primers (ND-440, 5′-TTA CCA TAG CAC TAA TCC-3′ ; ND-310, 5′-CCA ATA GKA TCA GCA CGC CTA C-3′ ; ND-830, 5′-GTY ATR ATC TCC AAC ACT TAC-3′ ; and ND-920, 5′-CAC TAA CAT GAC TAT CAA-3′ for the ND fragment; AMEL328F 5′-CAT GAA ATA TAG ACT CGC TAA-5′ , AMEL604F 5′-GCT CCT GCT CTT CTT TG-3′, AMEL1108F 5′-AAC AAT ATT TTG AAG TGT GGG-3′ , and AMEL1116R 5′-TTA TAA TAC CCA CAC TTC AAA-3′ for the Amelogenin X fragment). Sequences were edited, trimming ends with ambiguous peaks, and aligned with the program SEQUENCHER. Uncorrected p distance matrices were generated using the program PAUP* [52] . Sequences were deposited on GenBank ( Table 5 ).

Acknowledgments

CPG is grateful to all the museum curators who have helped in studying osteological material, and who have been acknowledged in a previous publication [1] ; to staff of San Diego and Dvur Kralove zoos for their kindness in providing materials, and to Steve Kingswood, Ann Oakenfull, the late Arlene Kumamoto, the late Luděk Dobroruka, Kees Rookmaaker, Kes Hillman-Smith, Jo Myers-Thompson, and the late Peter Grubb, for discussion. JR is very grateful to Petr Benda (National Museum, Praha), Ivana Cinková (Faculty of Science, Palacky University in Olomouc), Luděk Čulík (Dvur Kralove Zoo), Jiří Hrubý (Dvur Kralove Zoo), Pavel Král (Usti nad Labem Zoo), Kristina Tomášová and zoo keepers from Dvur Kralove Zoo for kind assistance with the study of living individuals, and/or valuable information.

We would also like to thank Don J. Melnick for access to genetic samples and use of the Center for Environmental Research and Conservation (CERC) genetic laboratory, Columbia University, New York; and Juan Carlos Morales, San Diego Zoo, Eric Harley, David Cumming, Raoul Du Toit, Wildlife Department of Zimbabwe, Perez Olindo, David Western, and the Department of National Parks and Wildlife Management of Kenya, for providing samples for genetic analysis from their routine research, and Jennifer Pastorini for help with the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

Funding: JR was partly supported by Czech grant No. MSMT 6007665801; neither of the other authors were financially supported for this work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Energy Innovation Hub teams will emphasize multi-disciplinary fundamental research to address long-standing and emerging challenges for rechargeable batteries

WASHINGTON, D.C . - Today, the U.S. Department of Energy (DOE) announced $125 million in funding for two Energy Innovation Hub teams to provide the scientific foundation needed to seed and accelerate next generation technologies beyond today’s generation of lithium (Li)-ion batteries. These multi-institution research teams, led by Argonne National Laboratory and Stanford University, will develop scientific concepts and understanding to impact decarbonization of transportation and incorporation of clean energy into the electricity grid.

Rechargeable batteries, such as Li-ion and lead-acid batteries, have had a tremendous impact on the nation’s economy. Emerging applications will require even greater energy storage capabilities, safer operation, lower costs, and diversity of materials to manufacture batteries. Meeting these challenges requires a better understanding of foundational battery and materials sciences to enable scalable battery designs with versatile and reversible energy storage capabilities beyond what is currently possible. Additional benefits may include mitigation of supply chain risks associated with the current generation of batteries.

"Providing the scientific foundation to accelerate this important research is key to our economy and making sure the U.S. plays a lead role in transforming the way we store and use electricity,” said Harriet Kung, DOE’s Acting Director for the Office of Science. “Today's awards provide our Energy Innovation Hub teams with the tools and resources to solve some of the most challenging science problems that are limiting our ability to decarbonize transportation and incorporate clean energy into the electricity grid."

The two Energy Innovation Hub teams are the Energy Storage Research Alliance (ESRA) led by Argonne National Laboratory and the Aqueous Battery Consortium (ABC) led by Stanford University. ESRA will provide the scientific underpinning to develop new compact batteries for heavy-duty transportation and energy storage solutions for the grid with a focus on achieving unprecedented molecular-level control of chemical reactivity, ion selectivity, and directional transport in complex electrochemical cells. ABC will focus on establishing the scientific foundation for large-scale development and deployment of aqueous batteries for long-duration grid storage technologies.  Both of these teams will prioritize study and use of Earth-abundant materials to mitigate supply chain risks.

Both Energy Innovation Hubs teams are comprised of multiple institutions, including Historically Black Colleges and Universities (HBCUs) and other Minority Serving Institutions (MSIs). The projects provide an outstanding opportunity for workforce development in energy storage research and inclusive research involving diverse individuals from diverse institutions. 

The teams were selected by competitive peer review under the DOE Funding Opportunity Announcement for the Energy Innovation Hub Program: Research to Enable Next-Generation Batteries and Energy Storage. While focused on basic science, the Funding Opportunity Announcement was developed in coordination through the DOE Joint Strategy Team for Batteries.

Total funding is $125 million for awards lasting up to five years in duration. More information can be found on the Basic Energy Sciences program  homepage and  Energy Innovation Hubs page.

Selection for award negotiations is not a commitment by DOE to issue an award or provide funding. Before funding is issued, DOE and the applicants will undergo a negotiation process, and DOE may cancel negotiations and rescind the selection for any reason during that time. 

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Open Access

Peer-reviewed

Research Article

Anthropogenic Influences on Conservation Values of White Rhinoceros

* E-mail: [email protected]

Affiliations Scientific Services, South African National Parks, Skukuza, South Africa, Rhino Action Group Effort, Johannesburg, South Africa

Affiliation Scientific Services, South African National Parks, Skukuza, South Africa

Affiliation Rhino Action Group Effort, Johannesburg, South Africa

• Sam M. Ferreira, 
• Judith M. Botha, 
• Megan C. Emmett

• Published: September 27, 2012
• https://doi.org/10.1371/journal.pone.0045989
• Reader Comments

White rhinoceros (rhinos) is a keystone conservation species and also provides revenue for protection agencies. Restoring or mimicking the outcomes of impeded ecological processes allows reconciliation of biodiversity and financial objectives. We evaluate the consequences of white rhino management removal, and in recent times, poaching, on population persistence, regional conservation outcomes and opportunities for revenue generation. In Kruger National Park, white rhinos increased from 1998 to 2008. Since then the population may vary non-directionally. In 2010, we estimated 10,621 (95% CI: 8,767–12,682) white rhinos using three different population estimation methods. The desired management effect of a varying population was detectable after 2008. Age and sex structures in sink areas (focal rhino capture areas) were different from elsewhere. This comes from relatively more sub-adults being removed by managers than what the standing age distribution defined. Poachers in turn focused on more adults in 2011. Although the effect of poaching was not detectable at the population level given the confidence intervals of estimates, managers accommodated expected poaching annually and adapted management removals. The present poaching trend predicts that 432 white rhinos may be poached in Kruger during 2012. The white rhino management model mimicking outcomes of impeded ecological processes predicts 397 rhino management removals are required. At present poachers may be doing “management removals,” but conservationists have no opportunity left to contribute to regional rhino conservation strategies or generate revenue through white rhino sales. In addition, continued trends in poaching predict detectable white rhino declines in Kruger National Park by 2016. Our results suggest that conservationists need innovative approaches that reduce financial incentives to curb the threats that poaching poses to several conservation values of natural resources such as white rhinos.

Citation: Ferreira SM, Botha JM, Emmett MC (2012) Anthropogenic Influences on Conservation Values of White Rhinoceros. PLoS ONE 7(9): e45989. https://doi.org/10.1371/journal.pone.0045989

Editor: Matt Hayward, Australian Wildlife Conservancy, Australia

Received: April 17, 2012; Accepted: August 28, 2012; Published: September 27, 2012

Copyright: © Ferreira et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: Primary funding forms part of the annual budget of SANParks, the primary implementing agency that has management authority over the study area, Kruger National Park. Managers of SANParks that provided the funding through budget decisions had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The Rhino Action Group Effort is a Civil Action Group that originated from public outcry against rhino poaching in South Africa. SMF is chairman of the Committee and ME is a member representing visual media. RAGE’s mission is to facilitate a range of support from the private sector to government institutions by coordination of information, funding and expertise complimenting the National Wildlife Crime Reaction Unit and associated agencies’ curbing of rhino poaching in South Africa, and change attitudes to the use of rhino horn through information and awareness campaigns. Membership of the committee is voluntary and carries no financial gains. Committee members carry all cost associated with traveling for meetings against their own accounts. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials.

Introduction

Iconic species that have valuable assets, such as horns or pelts, suffer greatly from human persecution [1] . African mega-herbivores epitomize threats posed by such human persecution. The use of ivory, for instance, has for centuries influenced elephant Loxodonta africana abundance and behavior [2] , while perceptions about medicinal properties of rhinoceros (rhino) horn [3] made several rhino species lucrative targets [4] . Modern commercialization as well as technological advances facilitated the exploitation of biological resources [5] . The end result is that, globally, biological exploitation is a key driver of declines in a range of taxa [6] . Most notably are Africa’s large mammals, even in protected areas [7] .

Species with specific features are likely to be most at risk when biological exploitation is commercial. These include non-renewable assets ( e.g. elephants with ivory), small populations ( e.g. tigers Panthera tigris ), and slow life-histories ( e.g. rhinos). Potential threats to the persistence of white rhinos ( Ceratortherium simum ) in the Kruger National Park, a population stronghold for this species [4] , reflect some of these challenges. Poaching of white rhinos has increased dramatically since 2006 [8] most likely fueled by the recent increase in the value of rhino horn [9] . International trade in rhino horn remains prohibited, while trade within most countries is also illegal [10] . Even so, the value of rhino horn is likely to provide complex incentives to criminal elements [11] .

In addition, conservation agencies seek to restore degraded ecological processes. If this is not possible, they seek to mimic outcomes of impeded ecological processes [12] such as the influence that resource distribution has on the spatial use, associated intensity of landscape use and cascading ecological effects of mega-herbivores [13] . Resource distribution and availability can be altered through fences and water provisioning [14] which may have detrimental effects on conservation objectives through impeded spatial and demographic responses of mega-herbivores. Conservationists remove excess individuals generated by impeded population responses and have an option of using these for the establishment of other populations or, alternatively where wildlife can be traded, making these available for sale. Reconciliation of apparently contrasting biodiversity and financial objectives in such a way provides revenue that plays a key role in sustaining conservation areas [15] . Managers of Kruger National Park, a protected area with numerous additional water points [16] , use white rhinos within this framework to achieve biodiversity objectives and generate conservation revenue. Illegal removal of rhinos through poaching may also thus impede on other objectives that conservationists seek to achieve.

Although the driver of rhino poaching is primarily economic through the demand and supply ratio that determines the rhino horn market value and hence poaching incentive [11] , the consequences are varied. In the first instance is the threat that rhino poaching poses to the persistence of rhinos. The second consequence is the threat to other potential values such as the value of rhinos as a live commodity, the trade of which is legal [10] . Finally, society at large may experience variable consequences. In some instances societal degradation may result through associated organized crime [8] , but for the end-user of horn [3] , quality of living may increase through the placebo effect.

Within southern Africa, white rhinos are iconic and carry primarily two values – a purist conservation value, and a legal financial value (live rhino trade as well as rhino hunting). Here we evaluate threats posed by the present trends in poaching to the persistence of white rhinos in Kruger National Park, the largest population in the world. We also evaluate the potential consequences on contributions to populations elsewhere as well as traditional revenue generation through game sales. We then make suggestions on addressing these challenges in the short, medium and long terms.

Ethics Statement

The study made used of standard approved techniques to survey large mammals and did not require ethical approval since no animal was handled in the research.

Kruger National Park is situated in the low-lying savannas of the eastern parts of the Limpopo and Mpumalanga provinces of South Africa ( Fig.1 ). The Park covers an area of 19 485 km 2 , has mean annual rainfall that varies from 750 mm in the south to 450 mm in the north falling mostly during October to March [17] . Soils are derived from granite and gneiss deposits in the west and nutrient-rich basalts in the east. Karoo sediment is present where granite and basalt soils join [18] .

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https://doi.org/10.1371/journal.pone.0045989.g001

Wooded savanna, with Sclerocarya caffra and Acacia nigrescens dominating the tree canopy comprises the bulk of the southern basalts, while mixed Combretum spp. and Acacia spp. dominate the southern granites. In the north Colophospermum mopane dominates all substrates. [19] . The underlying geology and vegetation defines 35 landscape types ( Fig. 1 , [20] ).

Conceptual White Rhino Management Model

Kruger National Park has an extensive ecological management history [21] , most of which influenced resource distribution or access to resources. For instance, traditional landscape interventions interfere with vital rates of populations and fall into three categories: 1) those that affect dispersal such as fences and water provision [16] , [22] ; 2) those that affect survival such as culling, removals and water provision [23] ; and 3) those that affect fecundity such as contraception [24] and culling through reduced density-depend effects on birth rates [25] . Conservationists can address such effects of historical legacies by restoring spatial and temporal limitations and/or mimicking the effects of spatial and temporal limitations when restoration is constrained for several reasons [12] . This reflects a paradigm of the flux of nature which upholds that heterogeneity enhances diversity which enhances resilience [26] .

Although conservationists in Kruger are attempting to restore the variability in resource availability ( e.g. closure of waterholes), remaining constraints as well as population lag effects continue to generate adverse population responses particularly of mega-herbivores [27] . Mimicking the outcomes that result if these impeded factors were not present is what white rhino management in Kruger seeks to do. The mimicking effect could generate sources of rhinos for establishing populations elsewhere as well as provide opportunities to sell rhinos for financial gains. Herbivore populations may stabilize at different sizes depending on conditions imposed e.g. naturally limited, human altered through, for instance, landscape interventions, and harvested for maximum yield ( Fig. 2 ). When landscape interventions have removed population limiting and regulating mechanisms, abundances may increase. Responding to the excess created by impeded ecological limiting and regulatory factors provides for gains that will also enhance biodiversity conservation objectives. Most important is the temporal variability in this scenario that is relatively large and non-directional.

Note that a herbivore may stabilize at different population sizes depending on conditions imposed e.g. naturally limited (green line), constrained (red line) and harvested for maximum yield (blue line). The arrows indicate the likely available numbers for economic gain that will also enhance biodiversity objectives which focus on mimicking processes that has been impaired by landscape constraints. Most important is the temporal variability after stabilization that is wide and non-directional.

https://doi.org/10.1371/journal.pone.0045989.g002

Inducing spatial and temporal variation through managing numbers of a species may be enhanced through inducing source-sink dynamics [29] . Source-sink dynamics may lead to local instability, but regional stability [29] , a feature desirable if conservationists wish to maintain persistent biodiversity. However, such strategies may lead to drifts in age structures that may carry long term consequences for the population specifically if removal of excess is selective [30] . These concerns are pertinent for the white rhino management model that Kruger managers adhere too. In addition, poaching can significantly impede the implementation of this model.

Data Collection

We collated white rhino survey data for Kruger National Park from electronic databases (SANParks), unpublished reports and peer-reviewed publications. Fixed-wing based surveys covering 100% of Kruger National Park took place during 1960–1961, 1964, 1969–1993 as well as 1997. These total counts involved systematic low-level flying (≈300 feet above ground) with a light fixed-wing aircraft searching 64 blocks intensely and recording all rhinos encountered. During 1994 to 1996 similar approaches were used, but not all survey blocks were completed (SANParks, unpublished data).

From 1998 to 2010 counters used sample-based approaches [31] . With the exception of 2009, rhinos were recorded as part of the fixed-wing based annual herbivore survey of Kruger National Park each year. Sampling was based on flight paths with distance sampling estimating approaches [32] covering 15–22% of the Park. Stratified Jolly-Seber fixed-width estimating approaches using the same data resulted in 7.5–23.9% coverage of the Park. Note that transects had an east-west orientation and were spaced evenly across Kruger in a north to south configuration. Larger spacing leads to lower coverage and vice versa . The outcome is that all landscapes within Kruger had equal survey intensity relative to the extent of coverage in the Park.

We collated our final white rhino survey data set for 2009 from a black rhino ( Diceros bicornis minor ) block-based survey south of the Olifants River with coverage of 21.5% [33] . Counters also noted white rhinos in this survey. The survey comprised 3kmx3km blocks intensely searched from a helicopter observation platform.

Note that since 1998 spatially explicit records of white rhino survey data were kept which allowed us to focus on data since then in an attempt to understand landscape differences in white rhino dynamics. For the period from 1998 to 2011, we also collated records of poaching incidences (SANParks database, Corporate Investigation Services) as well as spatially explicit management removal records (SANParks database, Veterinary Wildlife Services) that included sexes and ages. Prior to 1998, we collated the total number of white rhino introduced or removed for ecological management reasons.

For 2009–2011, we annually defined the standing age distribution for white rhino during February and November each year. The survey targeted nine specific areas in the southern parts of the Kruger National Park. These areas had different histories of rhino removals for management purposes. We defined sinks (areas where rhinos have consistently been removed) and sources (areas directly surrounding sink areas) and controls (areas where rhinos were never removed and which are far away from sinks). The survey made use of helicopter-based search flights at a height of 350 feet flying at 60 knots and aimed to assign age (following [34] adapted to the diagrams of [35] ) and sex to at least 100 individuals in each area.

Data Analyses

We focused our analyses on data collated since 1998 when white rhino survey information was spatially explicit and poaching and removal statistics were well kept. For white rhino surveys conducted using fixed-wing aerial approaches (1998–2008 and 2010) we estimated population sizes in three ways. First, we used distance sampling approaches [32] that corrects for detection probabilities declining the further a rhino was from the flight path. Second, we used the same observations, but restricted our data to within 200 m either side of the flight path and applied a Jolly-Seber strip transect analytical approach [36] . In the third instance we allowed the strip to be 400 m on either side of the flight path and applied the Jolly-Seber strip transect analytical approach again. For all three analytical approaches, we obtained annual park-wide population estimates and 95% confidence intervals.

No formal white rhino surveys were conducted during 2009. White rhinos noted during the black rhino survey south of the Olifants River [33] allowed us to apply a Jolly-Seber strip transect analytical approach [36] that provided us with estimates of the number of white rhinos south of the Olifants River. Observers noted 89.8% of white rhino observations during 2008 and 90.6% of observations during 2010 south of the Olifants River in the fixed-wing based aerial surveys. We used the average of these two proportions to estimate a park-wide 2009 population size for white rhinos from the block-based survey south of the Olifants River.

To define a generalized trend for white rhinos in Kruger National Park since 1998, we checked how the confidence intervals of population estimates derived from each method of estimating abundances overlapped. We considered estimates as outliers for estimators that gave non-overlapping confidence intervals with the other estimators in a particular year. These outliers were subsequently excluded when defining the generalized trend. For estimators retained, we extracted 10000 random values for each year from the statistical distribution defined by the mean estimate and 95% confidence intervals. We combined these random values for all estimators in a specific year and calculated the mean as an estimate of the likely population size in a particular year. We also extracted the 2.5% and 97.5% percentile as estimates of the upper and lower 95% confidence limits respectively.

To check effect of management removal and poaching on rhino population structure we pooled all data for sink, source and control areas noted during February each year (2009–2011), and estimated the sex-specific proportion of calves (0–4 years), sub-adults (5–6 years) and adults (7 years and older). We then calculated similar sex-specific proportions derived for that year from the data on rhinos removed for management purposes. We estimated the average sex-specific proportions for the standing age distribution of all three years in February and compared these to the average sex-specific age distribution of all three years’ removals. For the poaching effect, we only had data available for 2011 and we used a similar sex-specific comparison of poached age distributions with the standing age distribution of the population in 2011 only.

We anticipated that if management removals are key drivers of rhino population dynamics, sex and age structure should differ between sources and sinks. To check this we estimated sex-specific proportions of calves, sub-adults and adults like before for sinks and sources separately each year from 2009–2011. By comparing average sex-specific proportions calculated by combining all three years between sources and sinks we could evaluate this prediction.

Because different landscapes are likely to impose different resource limitations on white rhinos, conservation managers removed rhinos where logistically possible and poachers do not kill rhinos evenly across landscapes, we anticipated that these factors will vary across landscapes. Our observations were not numerous enough to extract landscape-specific estimates applying distance sampling analytical techniques [32] . Neither was poaching statistics spatially explicit prior to 2011. However, our analyses (see later) illustrated that poaching effects are not detectable at the population level. Management removal statistics, in contrast, were spatially explicit. Thus, for this part of our analyses we used only estimates derived from Jolly-Seber analytical techniques [36] applied to strip width data collated for 200m on either side of flight paths. This removed the detection effect that distance sampling identified to which the 400m strip width was vulnerable. We fitted exponential and equilibrium models as before for each landscape using maximum likelihood approaches [37] and used Aikaike Information Criteria [39] to choose which model fits the available data the best.

In addition, we calculated what the exponential population growth was in each landscape since 2006, the period when most aggressive removal of white rhinos by managers took place. We then asked how these growth rates associated with abundance, the ratio between abundance and predicted K for each landscape from the fitted equilibrium models, and the number of rhinos removed. We transformed the ratio (inverse) and number of rhinos (natural logarithm) to linearize the potential relationship with growth rate. We then used multiple linear regression analyses to evaluate several combinations of variables as potential explanations for variation in population growth rate between landscapes using model selection procedures as before [39] . Abundance serves as an index of potential statistical effects, specifically small populations, on population growth, while the ratio measure serves as an index of density-dependent population effects.

Historic Trends

Park managers introduced 351 white rhinos between 1960 and 1972 and started to remove rhinos for donations to other conservation areas and zoological gardens during the mid 1980s ( Fig. 3A ). Since the late 1990s, a large fraction of the white rhinos removed was sold to generate conservation revenue. By the end of 2010, a total of 1402 white rhinos have been removed from the Park.

https://doi.org/10.1371/journal.pone.0045989.g003

Even so, rhinos continue to colonize Kruger National Park with the percentages of landscapes on which counters noted rhinos continuing to increase from 1998 to 2010 ( Fig. 3B ). During this period counters were encountering rhinos in new landscapes at a rate of 1.19 (95% CI: 0.91–1.41) landscapes per annum. By 2010, 77.1% of the Park’s landscapes had white rhinos present.

Incidences of poaching were relatively low from the 1960s until a dramatic increase since 2006 ( Fig. 3C ). Well kept records since 1998 illustrate that poaching incidences increased exponentially per annum (y = 0.042e 0.616x , R 2  = 0.89, F 1,12  = 17.68, p <0.01). During 2011, 252 white rhinos were poached in the Park.

Since the 1960s the number of white rhinos in Kruger National Park has been increasing ( Fig. 3D ). This was also the case for different survey approaches and application of different estimators to survey data from 1998 onwards ( Fig. 4A ).

We provide 95% confidence intervals (error bars) for different survey platforms and estimating techniques (A). Following estimator averaging, we present the generalized trend in white rhino population estimates (B). The solid thick line is the best fit model (see Table 1 ). We also present the predicted estimates if no removals or poaching took place (solid thin line), if no removals took place (thin broken line) and if no poaching took place (thin stippled line).

https://doi.org/10.1371/journal.pone.0045989.g004

Generalized Population Trend from 1998 to 2010

Jolly-Seber estimates derived from fixed-width strip surveys with strips 400 m wide on either side of the flight path were consistently lower than those derived from all other estimators ( Fig. 4A ). These were excluded and remaining estimator averaging suggested that the white rhino population in Kruger National Park increased from 1998 to 2008, but appears to fluctuate non-directionally since then ( Fig. 4B ) as the equilibrium model ( Equation 2 ) was best suited to explain the available data ( Table 1 ). During 2010 we estimated that 10621 (95% CI: 8767–12682) white rhinos lived in Kruger National Park.

https://doi.org/10.1371/journal.pone.0045989.t001

Anthropogenic Effects

If poaching and management removals did not take place, significantly more white rhinos would have lived in Kruger National Park ( Fig. 4B ). This effect, however, was only detectable during 2009 and 2010, when predicted estimates in the absence of anthropogenic factors were higher than the upper confidence limits of population estimates then. In the absence of both these factors, a mean estimate of 13794 rhinos (observed population size is 23.0% in reduction of potential population size) may have been noted during 2010.

Considering poaching and management removals separately resulted in only management removals having a detectable effect on white rhino population sizes during 2009 and 2010. The effect of poaching alone resulted in predicted estimates in the absence of poaching falling within the 95% confidence intervals of population estimates derived from white rhino survey data. In the absence of management removals, but with poaching present, a mean estimate of 13289 (20.1% reduction) may have been noted for 2010, while no poaching, but with management removals, would have resulted in a mean estimate of 11525 (7.8% reduction) white rhinos during 2010.

Managers and poachers targeted different ages of rhinos – managers tend to remove a higher proportion of sub-adult females (♂: z = 1.01, p = 0.84; ♀: z = −6.42, p<0.01) than what is available, but fewer adults (♂: z = −3.65, p<0.01; ♀: z = −2.90, p<0.01) ( Fig. 5 ). A differential effect on calves is not statistically detectable (♂: z = 0.48, p = 0.68; ♀: z = 1.06, p = 0.86). Poachers in turn targeted proportionally more adults of both sexes (calves ♂: z = −2.87, p<0.01; ♀: z = −2.87, p<0.01; sub-adults ♂: z = −4.34, p<0.01; ♀: z = −3.70, p<0.01; adults ♂: z = −2.13, p = 0.02; ♀: z = 2.54, p = 0.01). The dominant influences of management removals, however, were reflected in the comparative age and sex structure of source and sink areas. Sub-adult females made up a smaller proportion of the population in sink areas compared to elsewhere ( Fig. 5 ).

We also present age and sex proportions of white rhinos in source areas (solid bars, n  = 2315) and sink areas (grey bars, n  = 2725) noted during 2009–2011. If the bars separate at the vertical broken line then the proportion removed equals the proportion available.

https://doi.org/10.1371/journal.pone.0045989.g005

Landscape-specific Trends

Trends in white rhino dynamics varied substantially within landscapes ( Table 2 ). Eight of the 35 landscapes did not have sufficient data to fit population models. In most of these cases, the landscapes have not been colonized by white rhinos since their introduction into the Park in the 1960 s. Trends in population estimates in twelve of the remaining landscapes were best associated with equilibrium models, while trends in 15 landscapes were best described by exponential models.

https://doi.org/10.1371/journal.pone.0045989.t002

Differences in population growth within landscapes during 2006 to 2010 were primarily associated with abundance and the number of rhinos removed by managers ( Table 3 ). The lack of suitable landscape-specific poaching data constrained our analysis, but the relative little influence of detectable poaching effects on population scales negates this shortcoming. Density-dependence made very little contribution to explain variance in landscape-specific white rhino population growth rates.

https://doi.org/10.1371/journal.pone.0045989.t003

Predicted Anthropogenic Effects

SANParks’ rhino management model predicts that rhinos should be removed at a rate of 4.4% (95% CI: 0.9–7.8%) of the standing population size at any time. The present trend in the proportion of rhinos poached predicts an annual exponential rate of increase of 0.60 (95% CI: 0.55–0.66). Simulation results suggest that between 2011 and 2012, the number of rhinos poached will equal the number required to be removed for management purposes. The number of rhinos poached will exceed management requirements by 2013. If poaching continues then the population will decline significantly by 2016 (confidence intervals exclude zero) although point estimates of population growth are already consistently below zero by 2013. At that time between 505 and 735 rhinos may be poached annually ( Fig. 6 ).

The error bars represent 95% confidence intervals. The horizontal fine line is population growth of zero.

https://doi.org/10.1371/journal.pone.0045989.g006

Large scale exploitation of wildlife resources threatens several species’ populations globally [6] . Our analyses of population dynamics and influences of anthropogenic removals of white rhinos in Kruger National Park, the largest population in the world, suggest that poaching has already compromised some conservation values and may soon compromise the persistence of the population itself. The population may be fluctuating non-directionally as a result of white rhino removals and not density-dependent processes; poachers now remove as many rhinos as what management models seek to remove, but they target adult rhinos; and continued trends in poaching may lead to detectable population declines as soon as 2016. These findings about population trends rely heavily on the precision of rhino estimates. In our case, three different estimators vary and are of some concern.

Estimating abundances of species in a particular area of interest carries large challenges. This is because several sources of error prevent conservationists from obtaining exact counts [40] , [41] . For this reason, conservationists make use of numerous techniques including strip-transects [36] , block counts [33] , distance sampling [32] , dung counts [42] , mark-recapture techniques [41] , call-up surveys [43] , registration studies [44] and total counts [25] .

Using aerial observation platforms is a common approach for estimating population sizes of large mammals [40] , [45] . Hundred percent coverage of an area is usually referred to as a total count. This inherently assumes that it is a near exact estimate of the number of individuals of a specific species. The measure of how close an estimate is to the real number of individuals in a population is referred to as accuracy. Accuracy, however, has two components – bias and precision [46] . Bias originates from several sources, but is captured in three broad types.

Availability or concealment bias results when animals are present in the landscape, but not available to be sampled [40] , [45] . Detection bias results when animals are present and available, but there is considerable variation in detecting those [32] . Even though availability bias and detectability bias may be accounted for, observers have different capabilities introducing observer bias [40] , [41] , [47] . These three biases accumulate uncertainty and influence the second component of accuracy – precision which is the likely spread of estimates [48] given the uncertainties introduced by biases. An additional source of error comes from sampling [49] which all sample-based survey approaches are exposed to. In such instances surveyors are not covering a hundred percent of an area of interest. This is captured in standard errors of an estimate, the normal statistical description of a mean and the distribution of data that supports that mean [48] .

White rhino population estimates that we collated suffer at least from detectability bias – the lower estimates of 400 m strip transects result from detectability decreasing with distance from flight paths [32] . Strip-transects 200 m wide do not suffer from a similar bias and resulted in estimates similar to distance sampling estimates which corrects for detectability bias [32] . Given the values in the time series of estimates and the overlapping estimates of 200 m strip-transects, distance sampling and the one-off block count in 2009, we are confident that the trend defined by averaging these estimators best present the trends in white rhino population size within Kruger. The influence of observer bias and availability bias is unknown. However, for black rhinos these were estimated in 2009 and resulted in black rhinos being available for 90.3% of the time to be observed, but that observers will miss 3.8% of those [33] . Observer bias is likely to be the same for white rhinos, but availability bias may be different – a higher proportion of white rhinos will be available simply because of their preferences for habitats with less woody cover [50] compared to those which black rhinos prefer [51] .

The discrepancies between the fixed-wing 400 m wide strip transects and other estimators may also originate from relatively low survey intensities that ranged from 14.0% to 23.9% coverage of Kruger National Park. For elephants, survey intensities that define accurate estimates require at least 5–20% coverage, but 50% coverage for precise estimates [52] . Kruger conservation managers may benefit from definitions of optimal survey requirements for white rhinos annually given the threats posed to white rhinos at present and conduct annual estimates in that way.

Making use of robust surveys is of key importance because the challenges highlighted by the difference in estimates using different techniques dampens our estimation that 8767 to 12682 white rhinos lived in Kruger during 2010, but that these were unlikely to increase. This conclusion is vulnerable to the estimates for 2010, particularly given that the same methods disregarding the highlighted shortcomings noted declines from 2008 to 2010. The 2010 estimate may result from an anomalous count and, hence, may need to be excluded. Removing the 2010 estimate will then result in the data best explained by an exponential population model. More concerning would be if the comparable methods does not reflect an anomalous count or are immune to the biases highlighted earlier. That would suggest a dramatic decline of more than half of the population in two years. That magnitude of decline is unlikely given that the presence of a large number of conservation rangers in Kruger National Park would have detected large scale mortalities. For these reasons our model averaging may accommodate these uncertainties allowing us to conclude the most likely outcome of non-directional change in rhino abundances during recent years.

Within the above context we illustrated that rhino removal for management reasons left detectable population size effects given the relative imprecision of population estimates. During 2009 and 2010, detectably more white rhinos would have lived in Kruger if no management removals took place since 1998. We could not find a similar detectable effect for poaching primarily because the confidence intervals for white rhino population estimates are too wide.

In addition, we could find detectable population structure effects associated with white rhino management removals as areas of regular removal had fewer sub-adult cows compared to elsewhere in Kruger National Park. Indeed, managers typically removed relatively more sub-adult females in a particular year compared to what was available in the population at the time. Such selective removal may result in demographic cascades [30] and contribute to the large population size effect associated with management related removals. Selective removal may also impose evolutionary constraints [53] and have indirect long-term effects on genetic integrity of the population. Management removals thus need to reflect the standing age distribution to minimize inadvertent selective pressures.

Although we could not find detectable poaching effects on population size, we would find detectable potential poaching effects on population structure – poachers killed relatively more adults than were available in the population. Such size selection by poachers is well known for elephants [54] and ultimately induces structural as well as demographic changes that lead to critical thresholds when populations collapse rapidly [30] . Poaching may thus pose a significant threat to population persistence when populations decline to threshold levels.

What, however, is the difference between management removals and rhinos removed by poachers given that management removals influenced white rhino population dynamics substantially more than poaching did since 1998? Between 2011 and 2012, we predicted that the number of rhinos poachers will be killing equals the number of rhinos defined for removal by management wishing to mimic the outcomes of impeded ecological processes. One can argue that poachers are essentially doing management! Managers, however, remove those rhinos and use them as propagules for establishment of other rhino populations within their historical distribution range where they have been extinct for some time [55] , [56] . Such management removals thus make significant contributions to the recovery of the species as a whole. The entire white rhino world population has grown to more than 20000 white rhinos because of such approaches since the 1960 s initiated and advocated by the then Natal Parks Board [50] . In recent times, white rhinos from Kruger National Park are the primary sources of most privately-owned rhinos within the white rhino historical distribution. Privately-owned white rhinos comprised about 24.1% of all white rhinos in South Africa during 2010 [57] . Such restoration opportunities are lost when poachers do management!

In the second instance, managers sell white rhinos as live entities and use revenue generated to enhance protected areas [15] . SANParks, managers of Kruger, make use of game sales to augment a Parks Development Fund that support conservation infrastructure, management and research (SANParks, personal communications). Revenue generating opportunities are thus also lost when poachers do management!

In addition, poaching is not toned by ecological management models such as that used by SANParks or adaptive feedback loops [58] . Our analyses suggest frightening trends of continued increases in white rhino poaching pressure, a trend noticed world-wide for just about any natural resource that has relatively high financial value [1] , [59] . Poaching predicted for 2012 has already removed opportunities to contribute to range expansion and gain financially for Kruger National Park. We predicted that by 2016 the population itself will be declining if present trends in poaching continue. In 2009 and 2010, management in Kruger adapted and earmarked rhinos for removal after poaching effects have been accounted for as it is relatively easy to apply adaptive management to local aspects under the control of managers.

Dealing with poaching effects is significantly more challenging because the drivers are associated with factors determining the financial value of a natural resource commodity. Demand and supply are the key underlying determinants of financial value of commodities [60] . The link between the high ratio of rhino horn demand over supply resulting in a high commodity value [9] , exposes rhinos to criminal exploitation ( Fig. 7A ). Our results and predictions suggest that financially driven poaching incentives threatens the persistence of white rhinos as a species. Conservationists thus need to reduce the ratio of demand over rhino horn supply.

We also provide examples of trade scenarios and financial models (B) that make different predictions about influences on the demand and supply ratio and ultimately white rhino population persistence.

https://doi.org/10.1371/journal.pone.0045989.g007

Reducing demand carries significant challenges as it faces age-old traditional inertia [3] . Although approaches are limited, strong awareness, advocacy and education campaigns may greatly contribute to reducing demand particularly if these are not associated with strong traditions such as recently claimed medicinal cures for cancer [61] .

The management of supply through legalizing rhino sales carries enormous challenges ( e.g. philosophical constraints, existing CITES international agreements and national legislation, risks to other rhino species, lack of logistical and management systems, and a need for high level political intervention). Parts of these associate with relatively limited exploration of several forms of financial models and approaches (but see [62] ). By evaluating consequences of different scenarios for rhino populations as well as human livelihoods alike ( Fig. 7B ), international agreements such as CITES as well as national policy makers may be better informed to make decisions that curb the threats that poaching has to various conservation and societal values associated with white rhinos.

In the short to medium term, however, conservation authorities are left with eliminating supply, which is the key focus of present anti-poaching activities [57] . Our conceptual model predicts that poaching incentives should increase unless anti-poaching units can develop tactical responses that provide non-financial disincentives. For instance, low minimum wages result in little deterrent effects of fines or jail sentences [63] . In such instances, anti-poaching, often tactically re-active, carries no disincentive for a poacher to continue poaching [5] . Humanely challenging approaches, such as shoot-to-kill policies, often result [63] , the effectiveness of which is uncertain. The trends that we have noted in poaching of white rhinos suggest that eliminating or reducing supply through the present anti-poaching tactics may have limited influence on poaching incentives, whether financial or non-financial.

Our results flag potential declines of the white rhino population in Kruger National Park that may be a result of poaching. We have also illustrated that at least two conservation values – sources for establishment of other populations and revenue generation – have already been compromised. We propose better surveys to define population level effects more precisely. But more importantly we advocate more pro-active tactical anti-poaching approaches already in development [57] directed at curbing poaching incursions into protected areas. Ultimately though, the international conservation community will need to find innovative ways to reduce the ratio between demand and supply that defines the financial incentives for white rhino poaching. We advocate that these challenges are shared by all exploited natural resources globally.

Acknowledgments

We thank SANParks for making information available. Jenny Joubert provided data on white rhino management removals while Sandra Snelling provided the poaching statistics. We are grateful to Grant Knight and Charles Thomson as the helicopter pilots and all the section rangers of Kruger National Park for assistance in surveys. Numerous observers took part and their time and effort is greatly appreciated.

Funding Statement

SANParks funded all surveys for white rhinos and captures from the annual budget. The Park Development Fund provided additional financial support for the age- and sex-structure surveys, while the USFWS funded the black rhino survey of 2009.

Author Contributions

Conceived and designed the experiments: SMF. Analyzed the data: SMF JB. Contributed reagents/materials/analysis tools: JB ME. Wrote the paper: SMF JB ME.

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Septoplasty versus non-surgical management for deviated nasal septum: a systematic review and meta-analysis of randomized controlled trials

• Review Article
• Published: 04 September 2024

Cite this article

• Hosam I. Taha   ORCID: orcid.org/0009-0008-9192-4175 1   na1 ,
• Mohamed S. Elgendy   ORCID: orcid.org/0000-0003-3080-2875 1   na1 ,
• Mohamed R. Ezz   ORCID: orcid.org/0000-0002-2998-6155 1 ,
• Khalid Tolba   ORCID: orcid.org/0009-0001-4057-1671 1 ,
• Mahmoud El Safty   ORCID: orcid.org/0009-0004-8461-0435 1 ,
• Mohammad Al Diab Al Azzawi   ORCID: orcid.org/0009-0006-6776-6467 2 ,
• Basant E. Katamesh   ORCID: orcid.org/0000-0001-9992-2387 1 , 3 &
• Ebraheem Albazee   ORCID: orcid.org/0000-0003-1244-7769 4  

This systematic review and meta-analysis of randomized controlled trials (RCTs) aimed to evaluate the efficacy and safety of septoplasty versus non-surgical management for patients experiencing nasal obstruction due to deviated nasal septum (DNS).

We conducted a comprehensive search of PubMed, Scopus, Embase, Web of Science, Cochrane Library, Clinicaltrials.gov, ICTRP, and ISRCTN for relevant RCTs. The primary outcomes included the Nasal Obstruction Symptom Evaluation (NOSE) scale, Sino-Nasal Outcome Test (SNOT-22), Peak Nasal Inspiratory Flow (PNIF), surgical complications, and quality of life. Data were synthesized using RevMan 5.4 and STATA 18, with effect estimates presented as mean differences (MD) or risk ratios (RR) with 95% confidence intervals (CI). The study protocol was registered with PROSPERO (ID: CRD42024538373).

Our search identified 537 studies, of which 3 RCTs involving 721 participants met the inclusion criteria. The meta-analysis revealed that septoplasty significantly improved NOSE and SNOT-22 scores compared to non-surgical interventions at 6 and 12 months of follow-up, despite no notable differences at 3 months post-treatment. No significant difference was observed regarding nasal flow assessed by PNIF. The rate of complications was low, ranging from 0.31% (revision rate) to 4.12% (bleeding and infection rates). Additionally, our qualitative synthesis showed an improvement in the quality of life at 6 and 12 months in the septoplasty group compared with the non-surgical group.

Conclusions

This systematic review and meta-analysis of 721 patients revealed the efficacy of septoplasty, with or without turbinate surgery, in improving nasal obstruction symptoms at 6 and 12 months. Additionally, septoplasty consists of a relatively low rate of complications such as bleeding, infection, and septal perforation. Furthermore, a low revision rate was found. Septoplasty improved the quality of life, especially after 6 and 12 months. However, our findings should be interpreted with caution, and further research is needed to consolidate our results.

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Dąbrowska-Bień J, Skarżyński PH, Gwizdalska I et al (2018) Complications in septoplasty based on a large group of 5639 patients. Eur Arch Oto-Rhino-Laryngology 275:1789–1794. https://doi.org/10.1007/s00405-018-4990-8

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Acknowledgements

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Hosam I. Taha and Mohamed S. Elgendy contributed equally to this work and share the first authorship.

Authors and Affiliations

Faculty of Medicine, Tanta University, Tanta, Egypt

Hosam I. Taha, Mohamed S. Elgendy, Mohamed R. Ezz, Khalid Tolba, Mahmoud El Safty & Basant E. Katamesh

Faculty of Medicine, National Ribat University, Khartoum, Sudan

Mohammad Al Diab Al Azzawi

Research Scholar, Mayo Clinic, Rochester, MN, USA

Basant E. Katamesh

Kuwait Institute for Medical Specializations (KIMS), Kuwait City, Kuwait

Ebraheem Albazee

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Hosam I. Taha and Mohamed S. Elgendy contributed to study conception, study design, data collection, data analysis, write up of original draft of manuscript, and review of manuscript for editorial and intellectual contents. Mohamed R. Ezz, Khalid Tolba, Mahmoud El Safty, and Mohammad Al Diab Al Azzawi contributed to literature review, data collection, and review of manuscript for editorial and intellectual contents. Basant E. Katamesh and Ebraheem Albazee contributed to supervision and review of manuscript for editorial and intellectual contents. All authors read and approved the final draft of manuscript.

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Correspondence to Ebraheem Albazee .

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Taha, H.I., Elgendy, M.S., Ezz, M.R. et al. Septoplasty versus non-surgical management for deviated nasal septum: a systematic review and meta-analysis of randomized controlled trials. Eur Arch Otorhinolaryngol (2024). https://doi.org/10.1007/s00405-024-08937-x

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DOI : https://doi.org/10.1007/s00405-024-08937-x

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Research: When Bonuses Backfire

• Dirk Sliwka
• Timo Vogelsang

How to rethink your incentive strategy and reward employees in ways that actually motivate them.

Why do bonuses sometimes backfire? It’s because each incentive design choice both signals information about your own beliefs and intentions as an employer and shapes the signaling value of employee behavior within the organization. If you don’t think through these signals carefully, you may end up approving a bonus scheme with results that are the opposite of what you intend. This article offers a way to help you align the signals your incentive scheme sends with your performance goals.

More than 30 years ago, author and lecturer Alfie Kohn, in a rather controversial but often cited HBR article , claimed that “rewards typically undermine the very processes they are intended to enhance.” Yet until recently, nearly all scientific studies that have documented such “backfiring” effects have been confined to laboratory experiments or field settings outside of the firm. This may cause some to question whether these effects are really present in commercial contexts. Our new research, which consists of two large field experiments in retail organizations, demonstrates that they do indeed occur.

• DS Dirk Sliwka is a professor of management in the Faculty of Management, Economics, and Social Sciences at the University of Cologne in Germany
• TV Timo Vogelsang is an Associate Professor of Managerial Accounting at the Frankfurt School of Finance and Management in Germany

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JD Vance got ‘single cat women’ all wrong. Our research shows they wouldn’t vote for him anyway

Professor of Sociology and Founding Director of The Future of Work Lab, Podcast at MissPerceived, The University of Melbourne

Associate Professor of Political Science, Oregon State University

Associate Professor of Sociology, Oregon State University

Disclosure statement

Leah Ruppanner receives funding from the Australian Research Council. She is also the host of MissPerceived podcast, where she discusses gender research.

Christopher Stout and Kelsy Kretschmer do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

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The Trump/Vance ticket seems to have a problem attracting the support of women voters . In fact, recent polling shows women in the battleground states report 17 points less support for the Trump/Vance ticket than men .

When the data are split generationally, this gender divide becomes even more stark. Among those aged 18–29, there is a 51-point gender gap . Women in this age bracket support Trump at just 13 points, while women support Harris by 38 points.

There are likely numerous reasons for this growing gender gap, including the historic nature of Harris’ campaign and Trump’s numerous well-documented conflicts with women . However, one source of these polling deficits may be tied to Trump’s vice presidential nominee’s attack on single women and women without children.

As JD Vance emerged as the vice presidential pick for the Trump ticket, a 2021 Fox News Interview resurfaced in which he said the country was being run by a

bunch of childless cat ladies who are miserable at their own lives and the choices that they’ve made and so they want to make the rest of the country miserable, too.

In another interview around the same time, he questioned whether the president of the American Federation of Teachers should be working on school policy , because she did not have children.

The challenge for the Trump/Vance ticket is that, as our research shows , single women are much more likely to see their futures as connected to other women. As a result, they are more likely to support the Democrats. Shaming them for their single status only reinforces their connection to other women, and a vote for Harris.

We are connected: the role of gender linked fate

Our research team has been investigating the concept of “gender-linked fate”, or agreement with the idea that what happens to women in general will affect women’s own lives. This work follows previous research in the US that found Black voters tend to report higher levels of racial-linked fate , or seeing their futures and fates as intrinsically tied to those of other Black people. This link helps explain why Black voters in the US consistently vote Democratic, despite coming from diverse educational and income backgrounds.

We used the 2012 American Election Survey to see if women’s levels of gender-linked fate predicted their political affiliation. And, we found that one group was a standout in their exceptionally high rates of gender-linked fate: single White and Latina women. More than three-quarters of White and Latina single women reported that their futures were tied to what happened to women in general. One in three reported that influence was significant.

So, single women felt particularly connected to other women. Black women’s universally higher levels of gender-linked fate meant that their marital status had little impact on their levels of connection to other women.

We then looked to see if levels of gender linked fate helped explain political ideologies, or levels of conservatism and progressivism, and political party support. We found single women’s higher levels of gender linked fate helped explain why they held more progressive attitudes and were less likely to identify as Republicans than their married counterparts.

Women see the hardships other women ensure

So, JD Vance is right – single women are less likely to be conservative and vote for his ticket. But, it has nothing to do with them being miserable. Rather, they have a unique view of the experiences of woman in a society they feel is stacked against them. We aren’t the only ones to show this. Previous research shows single women are more likely to experience poverty and, despite being more likely to work than married women, earn less .

As a result, single women are more likely to support policies that advance opportunities for all women, especially as they have to rely more heavily on their own incomes. They are also more likely to see gender discrimination at work and gender pay gaps that aren’t tied to individual successes or failures.

They are more likely to be pro-choice , in part because they see their futures and fates as more connected to other women. And women who see themselves as connected to other women are more likely to vote for women .

Group-based attacks are not a winning strategy

Attacking women for their life choices is likely to increase levels of group consciousness among women. When women feel marginalised, they tend to display higher levels of gender-linked fate . Vance trivialising the value of the work of women without children is likely to highlight the marginalisation they feel in society. This greater recognition of the shared bonds that are forged from shaming likely heightens their sense of connection to others who share their gender and circumstance.

This sense of gender-linked fate, which is likely furthered by these comments, will amplify support for the Democratic ticket. Not only should higher levels of gender link fate lead women to feel a greater disconnect between their preferences and the Republican Party’s positions around reproductive rights and gender equity, but it may also increase support for the Harris campaign’s attempt to break the glass the ceiling.

To learn more about research on women in politics, tune into this week’s episode of MissPerceived podcast .

• 2024 US election

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Letting funding for the All of Us research program lapse will cost the U.S. far more than it saves

Investing in preventive medicine and drug target discovery now will save lives and billions of dollars.

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By Pradeep Natarajan

Sept. 3, 2024

Natarajan is the director of preventive cardiology at Massachusetts General Hospital.

I was in high school when I first encountered the ruthlessness of the number one killer in the U.S. A close friend of mine, then only 16 years old, witnessed his father having a heart attack while checking the mail. Despite desperate attempts at CPR on the driveway, he wasn’t able to save his dad, a seemingly healthy man in his early 40s. That event put me on a path to become a cardiologist. Twenty-five years later, as a physician at Massachusetts General Hospital in Boston, I’m still seeing young patients having heart attacks, though they often have nothing in their health profiles to indicate increased risks.

As a preventive cardiologist, I wish I had a better way to identify patients who have a heightened risk for heart disease earlier so that they can take action before it’s too late. Prevention is the best medicine — it saves lives and health care dollars — but in our current paradigm, we’re focused on treating conditions after they occur.

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Fortunately, there is a new, effective way to better find those at highest risk very early in life, well before they develop risk factors like diabetes or high blood pressure. My research group at Massachusetts General Hospital and the Broad Institute of MIT and Harvard, and many other labs, have been developing genetic tests that can predict disease risk well before disease becomes apparent, called polygenic risk scores.

These types of predictive tests and genetics-informed treatments hold enormous promise for the fight against heart disease, diabetes, cancer, and so much more. Polygenic risk scores have been developed for heart attack and other forms of heart disease, but they aren’t currently accurate for many segments of the U.S. population.

The only way to make these tools actually work for the diverse U.S. population is to study the health profiles of hundreds of thousands of Americans. Generating these profiles is precisely a key goal of All of Us, a federal precision-medicine research effort that’s now facing a potentially fatal funding cliff.

This world-leading initiative, launched in 2018, is recruiting 1 million volunteers from across the U.S. The project is collecting their health, medical, and genetic information, and making that large and invaluable dataset available to scientists like me so that we can find new drug targets and develop preventive tests from genetics for a wide range of diseases.

The data that All of Us has collected so far represents people from all across America, including those from rural and urban communities and from all walks of life. These people are helping us develop better polygenic risk scores and novel therapeutic strategies that will improve the health of all Americans for generations to come. But without full support from Congress, All of Us will only be able to generate roughly half of the genetic data it has promised. Less data from fewer communities means less accurate genetic tests and fewer new drugs that can keep people out of the emergency room.

All of Us faces a whopping 71% decrease in funding for the coming fiscal year, which starts Oct. 1, compared with its funding level just two years ago. That’s because a major source of its first round of funding, in the 2016 21st Century Cures Act, was designed with fluctuating budget levels over 10 years. This cut is but the start. With just two years left, the clock is nearly up entirely. While I am hopeful about recent efforts from two members of the House on a Cures 2.0 bill and from the Senate Appropriations Committee to restore All of Us funding to the FY 2023 level, it’ll be up to both chambers of Congress this fall to ensure this important program has stable funding to keep going.

All of Us is only half complete, and a loss of stable funding threatens its timeliness and impact. It is unclear how many more Americans will be able to sign up to contribute to this work; I worry that without the necessary support, recruitment levels will fall sharply and data generation will slow dramatically. 

This funding loss will be a blow for preventive medicine in another way, too, by starving the drug development pipeline of much needed new drug targets that are rooted in human genetics. Many in the drug discovery world are familiar with the story of PCSK9 inhibitors, which lower LDL cholesterol levels to help prevent heart disease. These treatments were first approved by the Food and Drug Administration in 2015, just 10 years after genetic studies — similar to the ones that All of Us data can empower — suggested that the PCSK9 gene would be a promising target for cholesterol drugs. The big difference with the full set of All of Us data is that it would include many more people from underrepresented populations, which likely harbor disease-associated gene targets that are yet to be discovered. Without this entire diverse dataset, the genetics community will miss out on opportunities to generate more drug discovery success stories like the PCSK9 one.

This program has another advantage: maintaining and extending this country’s global edge in the life sciences. Other countries with nationalized health systems, like the United Kingdom and Finland, are making progress toward their own large genetic and medical datasets, or biobanks, that reflect the health status of their populations. While this information is useful for researchers all over the world, it is insufficient for developing the genetic insights, diagnostics, and treatments that are most relevant for Americans, because it doesn’t account for the population diversity and unique experiences and environments of the American people the way that All of Us data would.

All of Us is a big bet on a better future. Genomics-based tools will be critical for preventing and treating disease. Better prevention and treatment would save lives, livelihoods, and money: for heart disease alone, the American Heart Association projects annual inflation-adjusted health care costs will triple in the next two decades, from $400 billion to $1.34 trillion.

By restoring funding to All of Us, Congress can help deliver on the promise of a better health care system, and better health for all Americans.

Pradeep Natarajan, M.D., is the director of preventive cardiology and the Paul and Phyllis Fireman endowed chair in vascular medicine at Massachusetts General Hospital (MGH), associate professor of medicine at Harvard Medical School, and associate member of the Broad Institute of MIT and Harvard. MGH and Broad are both institutional recipients of All of Us funding to advance research. Dr. Natarajan does not receive direct funding from All of Us.

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About the reporting

STAT’s investigation is based on interviews with nearly 100 people around the country, including incarcerated patients and grieving families, prison officials, and legal and medical experts. Reporter Nicholas Florko also filed more than 225 public records requests and combed through thousands of pages of legal filings to tell these stories. His analysis of deaths in custody is based on a special data use agreement between STAT and the Department of Justice.

You can read more about the reporting for this project and the methodology behind our calculations.

The series is the culmination of a reporting fellowship sponsored by the Association of Health Care Journalists and supported by The Commonwealth Fund.

Pradeep Natarajan

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