African leaf-eating primates 'likely to be wiped out' by climate change

The paper, published online by Animal Behaviour, pinpoints which species are most threatened by climate change in a series of new global maps. They show current and predicted distribution patterns of primates, comparing the populations according to their diet and the amount of enforced rest they are predicted to need.

They warn that Old World monkey populations in Africa will be hardest hit even by a very modest two degrees Celsius increase in global mean temperature, especially those whose diets are mainly leaf-based such as the beautiful colobine monkeys. In contrast, New World monkeys in South America will be virtually unaffected by a rise of two degrees in mean temperatures. However, even the South American species will begin to suffer if temperatures rise as much as four degrees Celsius (the currently predicted most extreme value) because suitable habitats will then become increasingly fragmented and small fragmented populations are more liable to chance risks of extinction.

These predictions are based on analyses of the ecological constraints that determine how much time animals are forced to rest. The researchers found that animals that have forced rest have less time to forage for food or engage in other biologically essential activities, such as forming friendships. Although most primates have adaptations that help them cope with the heat, they head for shelter and rest when the sun gets too hot. The researchers show that resting time is influenced by three main factors: the percentage of leaves in the animals' diet, temperature variation and mean annual temperature. When these three effects come together, susceptible species will be unable to cope and populations will go extinct.

The researchers used climate models coupled with an analysis of quantitative data on the behaviour, diet and group size of different primate species across the world. African monkeys and apes that have a high percentage of leaves in their diet are geographically more restricted even now, being confined to a relatively narrow region around the equator. However, fruit-eating species like the baboons and guenon monkeys of Africa typically have a much wider latitudinal range and can cope with a wider range of climatic conditions. This ecological separation between fruit- and leaf-eating species is much less obvious in the Americas, and so these species will be much less badly affected by climate warming. The contrast between the continents may be due to the fact that African fruit-eating species may have developed a particular ecological adaptation to more challenging habitats than those encountered by species in South America.

Lead author Dr Amanda Korstjens, from Bournemouth University, said: "The possibility that enforced resting time might have so strong an effect on where on the map a major mammal group is likely to survive has not previously been appreciated. This study suggests that the amount of time available for monkeys and apes to gather food and socialise may be a key factor when looking at possible effects of climate change on animal distribution patterns in the past and in the future."

Professor Robin Dunbar, from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford, said: "We often worry about deforestation and hunting as the two main factors threatening the extinction of primate populations, but these results suggest that even if we find ways to solve these problems, it may not save some species of monkeys and apes from extinction. Instead, we perhaps should worry about ensuring that we provide these species with habitats that are more in tune with their capacities to cope with climate change."

Dr Julia Lehmann, from Roehampton University, said: "At overall temperature increases of two and four degrees Celsius, the distribution of habitat suitable for species that eat a lot of leaves will be greatly reduced. The distribution of suitable habitat would become progressively restricted and increasingly fragmented. The scale of the effect is sufficiently large that the implications for the survival of the dietetically more specialised primates are worrying."