Study identifies pattern with greater proportion of extreme typical body weights in mammals linked to specialised diets
Rhinos are among the mammals at the most extreme ends of the size spectrum, and new research suggests that their specialised, ‘picky’ diet may have an evolutionary role.
A new paper published in Nature Ecology and Evolution led by researchers at the University of Birmingham is the first known study that has identified a link between body size in mammals, measured in weight, and a specialised diet.
Across 3,500 mammal species worldwide, the researchers found a pattern with a much higher proportion of the smallest and largest mammals that follow a particular diet. For example, the white rhino which typically weights around 2,000kgs, and feed almost exclusively on short grasses.
Species such as the white rhino could traditionally afford to be picky eaters on this basis, but modern challenges now threaten them towards extinction in many areas of their natural habitat on the African continent.
Meanwhile, mammals of intermediate size were far more likely to be dietary generalists. Whether herbivore, carnivore or omnivore, these generalists will feed on a wider variety of potential food options.
Dr Shan Huang from the University of Birmingham and lead author of the study said: “Our results show that dietary specialisation doesn’t favour ‘middle-of-the-road’ body sizes.
“Instead, specialists seem to be evolutionarily pushed toward extremes - either very small bodies that reduce risk and resource needs, or very large bodies that can sustain long-distance foraging and defend themselves against predators. Species such as the white rhino could traditionally afford to be picky eaters on this basis, but modern challenges now threaten them towards extinction in many areas of their natural habitat on the African continent.”
Specialists at intermediate sizes often lose out in competition with generalists, the study found. Being too big to benefit from small-size advantages, yet too small to support the extensive foraging that benefits the largest specialists, they are squeezed from both sides - a dynamic that shapes the ‘U-shaped’ pattern seen in mammal body size.
Xiang-Yi Li Richter from the University of Konstanz and co-lead author of the study said: “Bringing this study together really took an interdisciplinary team, because we wanted to connect what happens in populations day to day at the ecological time scale with the big evolutionary patterns we see over millions of years. Our mechanistic model shows how small-scale ecological interactions can add up to the global body-size patterns we observe across mammals. And importantly, it lets us go beyond simple correlations by teasing apart how several forces work together.”
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Full citation: Huang, S., Morozov, A., Eyres, A. et al. Diverging selection on body size in specialist terrestrial mammals. Nat Ecol Evol (2026). https://doi.org/10.1038/s41559-025-02959-2
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Assistant Professor in Paleobiology
Dr Huang studies large-scale biodiversity patterns over time, using data synthesis to explore historical and environmental drivers of change.
