Investigating Constraints on the Survival of Orangutans Across Borneo and Sumatra

Abstract

Orangutans are highly endangered. In order to implement effective conservation strategies for these species, it is crucial to understand fully what constrains their distribution. Here, we use a previously developed time budget model to investigate the factors constraining the orangutans' ability to inhabit different areas of Borneo and Sumatra, as well as the social group size they are potentially able to adopt in their habitats. This model uses data from 13 field sites, together with climate and environmental data, to predict the amount of time individuals would need to spend in each of four main activities -feeding, moving, resting, and socializing. We found that resting time, which was linked to both dietary constraints and forest cover, was a key behavioral limitation on orangutan distribution. The maximum possible group size predicted for orangutans was low over the entire range, indicating that ecological constraints limit orangutan sociality, and that even small changes to habitat quality may further reduce the maximum possible group size. The fact that the values are already approaching one in many locations and are low throughout both Borneo and Sumatra, suggests that orangutans are vulnerable to extinction over their entire current distribution.

Why are there so many explanations for primate brain evolution?

“…However, it is also limiting for another important reason, namely the fact that both foraging and social bonding are time consuming: though not widely appreciated, large-bodied mammals (and diurnal primates, in particular) may be more limited by time than by energy [ 19 ]. As a result, time is a major determinant of anthropoid biogeography [ 19 , 71 , 73 , 154 – 156 ]. Owing to the need to devote time to leaf fermentation, folivorous Colobus monkeys, for example, are unable to live in large groups because they do not have sufficient time to devote to social grooming at the level required to bond larger groups; modelling shows that if they switched to a more frugivorous diet, as their sister-genus Piliocolobus has done, they would free off sufficient time to live in groups as large as those found in Piliocolobus [ 154 ].…”

Declining Orangutans Population in the Unprotected Forest of Batang Toru

“…It shows that orangutan leave areas with high levels of human activity and migrate to the remaining undisturbed forest in Hopong 2 . Reduction of forest cover will reduce fruit availability for orangutans, which can impact the behaviour ( Carne et al 2015 ), in this case, orangutans migrate away from the disturbance area.…”

Four errors and a fallacy: pitfalls for the unwary in comparative brain analyses

“…In fact, in captivity, orangs are at least as social as gorillas, and most zoos house them in groups for precisely this reason (Lardeux-Gilloux, 1997). The species is solitary now only because, thanks to climate warming, it lives in a marginal habitat at the limits of its ecological tolerances (Carne, Semple & Lehmann, 2015). Using a (social) group size of N = 14 places the species exactly where its neocortex size predicts, but using a (foraging) group size of N = 1 leaves it far adrift of all other species.…”