Possible shift in macaque trophic level following a century of biodiversity loss in Singapore

Biodiversity loss in tropical forests is a major problem in conservation biology, and nowhere is this more dire than in Southeast Asia. Deforestation and the associated loss of species may trigger shifts in habitat and feeding preferences of persisting species. In this study, I compared the habitat use and diet of long-tailed macaque (Macaca fascicularis) populations in Singapore from two time periods: museum specimens originally collected between 1893 and 1944, and living macaques sampled in 2009. I collected hair and used stable carbon and nitrogen isotope analysis to identify temporal changes in dietary source and trophic position, respectively. δ(13)C ratios were virtually identical, suggesting that macaques foraged in similar habitats during both time periods. However, δ(15)N ratios decreased considerably over time, suggesting that macaques today feed at a lower trophic level than previously. This decline in trophic level may be because of the disappearance or decline of other species that compete with macaques for fruit. This study highlights the effect of biodiversity loss on persisting species in degraded habitats of Southeast Asia, and improves our understanding of how species will adapt to further human-driven changes in tropical forest habitats.