Resource partitioning and niche overlap between hoolock gibbon (Hoolock hoolock) and other frugivorous vertebrates in a tropical semi-evergreen forest.

Understanding how niche differences evolve in ecologically similar species and how these differences are maintained is a fundamental question in ecology. We studied resource partitioning and niche overlap between the hoolock gibbon (Hoolock hoolock) and other frugivorous vertebrates from April 2016 to January 2018 in Satchari National Park, Sylhet, Bangladesh. We examined the differences in their diet, niche breadth, niche overlap, and characterization of patch use. We recorded feeding events of gibbons and other frugivorous vertebrates using ad libitum sampling. Gibbons consumed 76 plant species including 32 non-fig fruits and 14 figs. Twenty-one competing frugivorous vertebrate species shared 10-70% of their food species with hoolocks. Competition for fruits was intense among gibbons, macaques, and hornbills, as fruits comprised more than 50% of their diet. The niche breadth of the gibbons varied across seasons. It was lowest during the rainy season (B = 0.39) when fruits were more readily available, and highest in winter (B = 0.58) when gibbons were less selective due to food scarcity. The niche overlap was highest between gibbons and northern pig-tailed macaques (O = 0.70), followed by gibbons and hornbills (O = 0.68). Feeding heights and substrate used varied significantly between gibbons and competitors. Gibbons may minimize competition by specializing on various food resources and using different forest patches.