Dietary Shifts, Niche Relationships and Interspecific Competition in Sympatric Grey Langur (Semnopithecus entellus) and Purple-faced Langur (Trachypithecus vetulus) in Sri Lanka
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Understanding how niche differences evolve in ecologically similar species and how these differences are maintained ecologically is a fundamental question in ecology. Interspecific competition has been shown to influence the behavior and ecology of organisms in a wide range of ecological communities. However, the broader role of interspecific competition in primate communities is unclear as relatively few studies have explored this question. This is especially true for folivorous primate communities, such as those of colobine monkeys, in which the influence of interspecific competition on aspects of the ecology of these monkeys is yet to be determined. In this dissertation, I present data and analyses on the dietary ecology, ranging behavior, and interspecific interaction in Trachypithecus vetulus and Semnopithcus entellus. I use this work to assess the possible role of interspecific competition on the behavior and ecology of these species. I specifically explored this issue by investigating: 1) the monthly variation in dietary overlap in relation to monthly resource availability, 2) interspecific interactions in relation to resource availability, 3) the influence of interspecific interaction on feeding effort, and 4) the influence of interspecific interaction on vertical habitat use patterns. In this study, both species showed similar feeding patterns when feeding on seasonal plant items, but showed a preference for fruit and flowers over leaves, a trend not reported in previous studies on these species. The langurs in this study also consumed a high proportion of flowers in comparison to other colobine monkeys, making this population one of the most florivorous colobine populations. In addition, both species preferred to feed on tree species that were relatively rare and showed clumped distributions. Clumped resource distributions have been suggested to promote within-group and interspecific competition. Home range overlap between T. vetulus and S. entellus was extensive. Although resource availability within the home ranges of S. entellus and T. vetulus were similar, the index of defendability: D) of S. entellus was higher than the index of defendability: D) of T. vetulus. This suggests that the two groups of S.entellus traversed their home range more intensely than T. vetulus. Trachypithecus vetulus travelled a relatively short distance on any given day in comparison to S. entellus and consequently utilized only a fraction of its total home range. The dietary overlap between S. entellus and T. vetulus showed considerable temporal variation in comparison to dietary overlap between other closely related primate species. There was no significant relationship between monthly dietary overlap of immature leaves and monthly immature leaf availability. However, dietary flower overlap was high during periods of flower availability and low during periods of flower scarcity. This observation was consistent with observations from other studies, which show competitors to reduce diet overlap in response to the decline in resources. On the contrary, dietary fruit overlap tended to be high during periods of fruit scarcity as both species converged on the same fruit tree species. However, these primates were never observed to occupy feeding trees at the same time. Interactions between S. entellus and T. vetulus occurred mostly during the period when fruit availability was low. These interactions resulted in a reduction in the proportion time devoted to feeding by T. vetulus. In addition, during these interactions T. vetulus was displaced from feeding trees, which also resulted in T. vetulus altering its vertical habitat use pattern. These observations demonstrate that S. entellus was dominant over T. vetulus during intergroup interactions and hence it is possible that the low level of mobility and the low intensity of home range use observed for T. vetulus, and dietary niche partitioning by these species are adaptations by these primates to mitigate ecological competition and promote coexistence.
Vandercone, Rajnish, "Dietary Shifts, Niche Relationships and Interspecific Competition in Sympatric Grey Langur (Semnopithecus entellus) and Purple-faced Langur (Trachypithecus vetulus) in Sri Lanka" (2011). All Theses and Dissertations (ETDs). 654.
Permanent URL: http://dx.doi.org/10.7936/K7PR7SZR