Energetics gives new insight into the decline of cheetahs

14 November 2014 by Louise de Bruin

An acclaimed international study looking into new reasons behind the dwindling numbers of cheetah in southern Africa had its inception at the University of Pretoria (UP). Before this study, it was commonly thought that cheetah numbers were declining partly as a result of larger predators stealing their prey, thus lessening the availability of food and forcing them to expend more energy in search of food. However, a recent study offers new insight into why cheetahs may become vulnerable with regard to their energy levels, which could affect their general health and well-being and result in their ultimate decline.

The conceptual ideas for this study developed several years ago when Dr Michael Scantlebury, then a postdoctoral fellow, was studying mole rats in collaboration with Prof Nigel Bennett, holder of the Austin Roberts Chair of Mammalogy. From their innovative research using doubly labelled water (DLW) to determine daily energy expenditure (DEE) on caste differentiation in mole rats, which was incidentally published in Nature, they thought it a good idea to extend the study to a more enigmatic species like the cheetah to generate greater exposure for their ground-breaking findings.

The DLW method is a technique in terms of which so-called ‘heavy’ water is injected into an animal to evaluate its water loss through urination, defecation and perspiration in order to determine the amount of energy expended. During such activities, animals also produce carbon dioxide (CO₂). By analysing the production of CO₂, energy expenditure can be determined. Scantlebury found that even if 25% of a cheetah’s food is lost through kleptoparasitism (food stolen by larger predators), the effects are not devastatingly detrimental, as assumed previously. What proves to have a far greater negative effect on the well-being of cheetahs is the distance they have to walk in search of food.

The study, which evolved into an international collaboration, studied the energetics of 19 free-roaming cheetahs (fourteen in the Kgalagadi Transfrontier Park, and five in the Karongwe Private Reserve near Hoedspruit). The results showed that, contrary to common wisdom, the energy output during a high-speed cheetah chase after prey is not excessive. Rather, it seems that the energy they use to locate food far outweighs that used during a chase. The authors of the paper suggest that human activity, rather than competition with larger carnivores, is the predominant reason for the decline of cheetahs. Cheetahs have a nomadic lifestyle with a vast range. Consequently the number of fences erected on farms and placed around reserves is imposes a tremendous restriction on their hunting opportunities, with a ripple effect on their energy budgets. Bennett says, ’Cheetahs, like all carnivores, tread an energetic tightrope and low energy has several negative consequences, which may affect the immune system, reproductive abilities and metabolism.’

An international study of this kind has many benefits, Bennett notes. Broad collaboration implies that more resources can be invested in the study, and input of experts from multidisciplinary fields can be obtained. A previous graduate and extraordinary professor at UP, Dr Gus Mills, and his wife Margie were instrumental in the fieldwork for this study done in the Kalahari. They were involved in a six-year intensive study of Kalahari cheetahs, and so the energy research was piggy-backed on their work. They could follow Kalahari cheetahs and collect important faecal samples, and also provide invaluable background data that was used to interpret the results of the energetics study.

According to Bennett, there is great promise in furthering the study and adapting the findings. Because this initial study was done in the extreme weather setting of the Kalahari, Bennett mentioned the value of monitoring cheetahs in other areas of their savannah habitat, such as parts of the Kruger National Park. It would also be interesting to look at areas with a higher density of prey. However, the importance of this study is not just that it has offered new insight into a species whose declining numbers have dwindled to less than 10 000. What this study also shows is the importance of tackling all angles of a situation. While man’s intention may have been good when designating and cordoning off areas for wildlife, the reality seems that when the environment is modified too drastically, adverse effects and unintended consequences often result.

Prof Nigel Bennett

November 14, 2014

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Researchers
  • Professor Nigel Bennett
    Professor Nigel Bennett has been at the University of Pretoria (UP) for 26 years. He holds a BSc (Hons) in Zoology, which he obtained at Bristol University in the UK, and undertook his PhD studies at the University of Cape Town.

    His research focus is animal physiology and behaviour using the African mole rat as his model animal. His work is directed primarily at studying the social regulation of reproduction in mole rats.

    Prof Bennett’s research record ranks him among the best researchers studying social regulation of reproduction in any group of mammals in the world. He has investigated cooperative breeding in mammals from a variety of perspectives. This multi-faceted approach has led to an integrated understanding of reproductive suppression in mole rats of a type that has not been achieved for any other taxa. His research has set the benchmark for our understanding of phylogenetic and ecological constraints that regulate reproductive success and social evolution in mammalian species.
    Prof Bennett has always been interested in why some organisms adopt a social lifestyle and others do not. As a young boy, he was fascinated by how wood ants worked for the common good of a queen. His interest in mole rats came about while he was an undergraduate at Bristol University, after he had read a seminal paper by scientist Jennifer Jarvis on cooperative breeding in the naked mole rat. Upon obtaining a position as a doctoral candidate, Prof Bennett wanted to see if this was a feature common to other African mole rats. He went on to study the Damaraland mole rat, and found it to have incredible social organisation similar to that of social insects and termites.

    Prof Bennett is now the world leader in African mole rat biology, particularly in reproductive physiology. A research milestone for him was discovering that breeding female naked mole rats orchestrate non-breeding males and females in the colony to exhibit high prolactin levels. This inhibits the release of hormones that stimulate the development of reproductive activities in the gonads, as evidenced by a lack of follicular development in ovaries and a reduction in numbers and motile sperm in testes. Prolactin also results in individuals exhibiting helping behaviour and cooperative care of the young.

    After nearly three decades of research on the reproduction of social African mole rats, Prof Bennett has not been able to determine how the breeding female actually inhibits reproduction in physiologically suppressed animals. This would be the magic bullet for potential contraception in humans.
    He leads a research group that strives to unravel how social evolution arose in African mole rats – solving this puzzle has important implications as to how social evolution arose among hominids. Essentially, it comes down to food acquisition and protection from predators, which is a central theme in social evolution in most mammalian groups.

    Two people influenced his career: Prof Brian Follett – who supervised Prof Bennett’s honours project and whose infectious enthusiasm for science and incredible lectures fired up Prof Bennett’s imagination – and Prof Jennifer Jarvis, who drove his passion to work on mole rats.

    In 2021, Prof Bennett was made an honorary member of the American Society of Mammalogists, a title bestowed on fewer than 100 luminaries in a century. He has been a visiting professor at the School of Chemical and Biological Sciences at the University of London’s Queen Mary College since 2005. More recently, he was a visiting professor at the Department of Zoology at King Saud University in Saudi Arabia.

    He is a member of the Academy of Science of South Africa, and a fellow of the Zoological Society of London, the Royal Society of South Africa and the African Academy of Sciences.

    Prof Bennett was awarded the UP Chancellor’s Medal for his research on three occasions and has received the Exceptional Academic Achiever Award for the past 14 years. He was also the recipient of the Zoological Society of Southern Africa’s gold medal and received the Havenga Prize for outstanding contributions to Life Sciences, awarded by the Academy of Science and Arts of South Africa. UP awarded him the University of Pretoria Commemorative Research Medal for being one of the top 100 scientists in 100 years of its existence.

    Prof Bennett has served as president of the Zoological Community of Southern Africa for two years. He is also editor-in-chief of the Journal of Zoology and a past editor of Proceedings of the Royal Society B: Biological Sciences. In 2013, he was the handling editor of Biology Letters, another Royal Society of London journal. He has published 433 papers in international peer-reviewed scientific journals, co-authored a specialist book published by Cambridge University Press and has penned 15 chapters in books.

    In his spare time, Prof Bennett travels to different countries in Africa to explore the wildlife. He particularly enjoys visiting the mountain gorillas in Rwanda and Uganda, and the eastern lowland gorillas of the Democratic Republic of the Congo. He is also an avid collector of African art and frequently visits markets to add to his collection.

    If he were not a researcher, Prof Bennett would have liked to have been a game warden in one of East Africa’s national parks to contribute to the protection of the incredible African fauna from poaching.

    ORCID ID: 0000-0001-9748-2947
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