A large-scale study of 47 species of monkeys and lemurs has found that climate change and deforestation are driving these tree-dwelling animals to the ground, where they are at higher risk due to lack of preferred food and shelter and may experience more negative interaction with humans and domestic animals.
Published in the journal The Proceedings of the National Academy of Sciences (PNAS), the study examined more than 150,000 hours of observation data on 15 lemur species and 32 monkey species at 68 sites in the Americas and Madagascar. Led by Timothy Eppley, postdoctoral associate at San Diego Zoo Wildlife Alliance, the study was a remarkable worldwide collaboration between 118 co-authors from 124 unique institutions, including Western anthropology professor Ian Colquhoun.
“This study began with a discussion among colleagues about how we’d noticed certain populations of arboreal primates spending more time on the ground,” said Eppley, “yet at sites with relatively less disturbance, members of the same species may never descend to the ground.”
One of Canada’s leading primatologists, Colquhoun is an expert of biological anthropology and has studied lemurs in Northern Madagascar since the 1990s.
“Human-caused habitat disturbance and habitat fragmentation is proceeding at such a rapid pace that those radical habitat changes outstrip any long-term ability for arboreal primate species to respond effectively to those habitat changes,” said Colquhoun.
The causes for these radical habitat changes are endless, said Colquhoun, citing large-scale industrial farming, lumber extraction, and major infrastructure projects like roads and hydro-electric dams as just a few examples.
Colquhoun investigates all aspects of primate ecology and behaviour and is particularly focused on the study of ethnoprimatology, the study of the interactions between human populations and adjacent nonhuman primate populations in countries where nonhuman primates are endemic.
The authors of the study collectively estimated the influence of ecological drivers on the level of terrestriality (time spent on the ground) in arboreal primates. The study found primates that consume less fruit and live in large social groups were more likely to descend to the ground. The authors suggest these traits act as a potential “pre-adaptation” to terrestriality. Furthermore, primates living in hotter environments, and with less canopy cover, were more likely to adapt to these changes by shifting toward more extensive ground use.
Many of these species are already burdened with living in warmer, fragmented and heavily disturbed environments that often have fewer available dietary resources. As climate change worsens and arboreal habitats diminish, the study suggests primates consuming a more generalized diet and living in larger groups may more easily adapt to a terrestrial lifestyle.
“It’s possible that spending more time on the ground may cushion some primates from the effects of forest degradation and climate change; however, for the less-adaptable species, fast and effective conservation strategies will be necessary to ensure their survival,” Eppley said.
The study also found that primate populations closer to human infrastructures are less likely to descend to the ground. Luca Santini from Sapienza University of Rome, one of the two senior authors of the study, said, “This finding may suggest that human presence, which is often a threat to primates, may interfere with the natural adaptability of the species to global change.”
The transition from an arboreal to terrestrial lifestyle has occurred previously in primate evolution, but today’s rapid changes are a serious threat.
“Though similar ecological conditions and species traits may have influenced previous evolutionary shifts of arboreal primates, including hominins, to ground living, it is clear that the current pace of deforestation and climate change puts most primate species in peril,” said Giuseppe Donati from Oxford Brookes University, the second senior author of the study.
A member of the Madagascar section of the Primate Specialist Group of the International Union for Conservation of Nature Species Survival Commission, Colquhoun is keenly interested in all aspects of conservation biology, particularly regarding the lemurs of Madagascar.
“This study shows the importance of having large areas of continuous protected habitat for lemurs and other arboreal species,” said Colquhoun. “There certainly are some good examples of reforestation projects supported by community involvement, mostly communities adjacent to national parks or forest reserves. If you get local support and buy-in, it is always a good sign for success going forward.”