My current and future work is taking place at Lake Nabugabo, Uganda where I am expanding my research contrasting social and ecological influences on social organization by comparing two very different species. Vervet monkeys (Chlorocebus pygerythrus) are primarily frugivorous but supplement their diets with insects. They show female philopatry and matrilines that form long-term coalitions to defend food. Since fruit is a high-quality, clumped and finite resource, theoretically, ecological factors should be paramount in determining grouping patterns and social behavior in vervet monkeys.
Angolan black-and-white colobus (Colobus angolensis ruwenzorii) are folivorous and likely show female dispersal, though very little work has been done on this species. C. a. ruwenzorii also show the formation of supertroops where smaller groups join together without overt agonism. The low-quality and ubiquitous nature of leaves should mean that social factors, such as sexual conflict and mate choice, are important influences on the grouping and behavior of Angolan colobus monkeys.
Focusing on these two species that vary in their diets, competitive regimes, and thus their social organization and structure will allow two case-studies to examine evolutionary outcomes of varied ecological and social factors. I am currently examining the foraging strategies of vervet monkeys using foraging experiments that utilize artificial food patches. This gives me the unique opportunity to manipulate food resource availability and design experiments to better understand the influences of various food attributes and food competition on vervet social behavior and movement decisions. This research also allows investigation of how vervets represent spatial information and use perceptual cues in decision making.
For the Angolan colobus, I have finished habituating two groups that often merge and separate and detailed behavioral observations are currently being collected. This subspecies forms large groups of hundreds of monkeys at montane sites but at lowland sites (including Nabugabo) smaller (~30) multi-male multi-female groups are seen that frequently fuse and fission. My initial objective is to determine whether C. a. ruwenzorii are forming a multilevel society (potentially the first in an African colobine) and if so, assess how many tiers of social organization are present. If this is a multi-level society, preliminary data suggests that the core units may be multi-male, multi-female, a social system not seen in extant primates except humans; raising many questions regarding the selective pressures leading to this system and the evolution of tolerant male relationships. This work will allow a greater understanding the larger impacts of ecological constraints and the strategies of group mates on the evolution of primate social systems.