Research Article Vasudev, D., Kumar, A., & Sinha, A. (2008). Resource distribution and group size in the common langur Semnopithecus entellus in southern India. American Journal of Primatology, 70(7), 680–689.

Blog Author: Ishika Ramakrishna

Key Takeaways:

  • The study investigated how food availability shapes group size and composition of the common langur in three connected southern Indian forests.
  • The research took place with gathered data on 94 groups of langurs, including both mixed-sex groups (comprising males and females) and all-male groups.
  • Adult male langurs exhibited stronger responses to changes in food resources compared to adult females, revealing intriguing social behavior patterns. Interestingly, the number of predators present in the environment did not seem to influence the group sizes of the langurs.
  • The study helped to understand how the distribution of food resources of the langurs can affect their populations and social lives, helping us learn how to conserve them better in the years to come.

Primates are complex, social beings. India is home to about 25 species of primates, and the common langur, Semnopithecus entellus, is one of the most widespread. Despite their relative abundance across central and south India, we still know very little about their behaviour, sociality, and what causes the diversity we see in how they form groups. What determines whether a group of langurs has a single adult male or several? Do the same factors affect the number of adult females in the same group? And how do these group compositions affect the lives of these langurs in the wild spaces they occupy?

Three primatologists – Dr. Divya Vasudev, Dr. Ajith Kumar, and Dr. Anindya ‘Rana’ Sinha – attempted to answer some of these questions back in 2006 with the help of diligent surveys of langur troops in Bandipur National Park, Mudumalai Wildlife Sanctuary and Nagarhole National Park in southern India, where they are abundant and commonly sighted. They believed that two factors could be influencing how langur groups were composed. The scientists looked at how the availability and distribution of resources affect the size and makeup of groups of common langurs in these three connected forests in southern India. They also explored whether the presence of predators and the risk of take-over influenced these group characteristics. This research took place with gathered data on 94 groups of langurs, including both mixed-sex groups (comprising males and females) and all-male groups.

To understand resource availability, the study assessed the types and quantities of trees that langurs typically eat. Common langurs are largely folivorous, and eat a wide diversity of leaves across different seasons. Two main measures to describe resource availability were used: the average area occupied by their food trees per plot and how much this varied across the grid. These measurements helped us understand both how much food was available and how evenly it was distributed across the langurs’ habitat. Their findings revealed interesting patterns. First, they observed that as the distribution of resources became more varied within a habitat, langur group sizes tended to increase. This suggests that when food is spread out rather than clumped together, langur groups might need to be larger to effectively find and utilize resources across their territory. On the other hand, in areas with abundant food, langurs were found in smaller groups.

Using the invaluable data from camera traps placed across the three study sites by CWS, Vasudev and her co-authors were able to arrive at the densities of leopards and tigers in the area – both important predators of the common langur. Interestingly, no significant evidence of the effect of predator presence on group size was found. This was contrary to their initial expectations, suggesting that other factors like resource availability may play a more prominent role in shaping langur social dynamics.

Another unexpected finding was how adult male langurs responded more significantly to changes in resource availability compared to adult females. Typically, in many animal species, females are more influenced by food availability due to their reproductive needs. However, this study indicated that adult male langurs might be more sensitive to changes in food resources, possibly due to their roles in defending territories or competing for access to females.

There were also differences in group characteristics between the different study sites. This could be due to variations in the langur subspecies present in each area, highlighting the importance of local ecological factors in shaping social behaviors among langurs.

Overall, this study provided valuable insights into how resource availability and distribution influence the group dynamics of common langurs in southern India. By understanding these relationships, we can now better predict how changes in habitat quality might impact langur populations and their conservation in the future, and adding in another missing puzzle piece in our understanding of Indian primate species.

To access the original article click here.

 Keywords: Western ghats, langur group dynamics, resource distribution, folivorous primates