Niche partitioning and coexistence of sympatric macaques in a fragmented habitat of the Upper Brahmaputra Valley, northeastern India

Abstract

How closely related species co-exist, especially under conditions of resource limitation remains an intriguing problem in ecology. Having to share space and resources, such species are expected to have evolved a variety of mechanisms to reduce competition. In this study, we examined the niche partitioning of three congeneric species, northern pig-tailed macaque Macaca leonina, the rhesus macaque Macaca mulatta, and stump-tailed macaque Macaca arctoides, in a tropical lowland rainforest fragment of less than 21 square kilometer, the Hollongapar Gibbon Sanctuary, northeastern India. We conducted behavioural observations on two troops each of the three species over 23 months from March 2008 to January 2010 resulting in 6,471, 11,062 and 16,723 individual scans of pig-tailed, rhesus and stump-tailed macaques respectively. We compared activity budgets and examined niche partitioning among the macaques along space and food axes. The activity budgets of three macaques shows differences in their feeding and foraging behaviours: the stump-tailed were active throughout the day, pig-tailed macaques were most active during mid-day while the rhesus macaques activity peaked after late afternoon. The rhesus macaque utilised the forest edge and surrounding areas whereas the stump-tailed and pig-tailed macaques use forest interiors. Pig-tailed macaques used significantly higher canopy strata, while stump-tailed macaques were predominantly terrestrial while rhesus macaques used the mid-lower canopy. Dietary overlap was highest between rhesus and pig-tailed macaques and lowest between pig-tailed and stump-tailed macaques. Rhesus macaques showed the broadest dietary niche breadth, whereas pig-tailed and stump-tailed macaques exhibited narrower and more specialised diets. Our results demonstrate that fine-scale partitioning of space and food resources facilitates the long-term coexistence of three congeneric macaques within a small and isolated rainforest fragment. These findings provide important insights into primate persistence and conservation in fragmented tropical landscapes.