Title

Ecological and social correlates of foraging decisions in a social forager, the bonnet macaque, Macaca radiata diluta

Date of Award

5-2002

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Larry L. Wolf

Keywords

Macaca radiata diluta, Foraging, Social forager, Bonnet macaque

Subject Categories

Behavior and Ethology | Zoology

Abstract

This study investigated ecological and social factors determining social foraging behavior in a diurnal, group-foraging primate, the southern Indian bonnet macaque, Macaca radiata diluta . It set out to ask how ecological and social variables interacted to influence the individual forager and whether either subset of the environment, ecological or social was more important in determining an individual's response. A series of foraging decisions was analyzed in response to experimentally induced variation in (1) ecological variables, including patch number, patch size, inter-patch distances, food search time, food quality and potential predation risk in habitat and (2) social variables, including social dominance rank, feeding group sizes, feeding group compositions and intra-group levels of aggression.

Social dominance emerged as an important organizing factor and determined which individuals fed at a given time in experimental trials. As long as habitats were relatively free from predation, dominant males, dominant females and sub-adult classes were well represented. Subordinate females were somewhat less represented while subordinate males were severely constrained and did not feed in most trials.

Similarly, social rank affected the spatial distribution of individuals across patches. Dominant males typically came into a feeding area and spread out uniformly over food patches. In sharp contrast, sub-adults aggregated into one or two patches. Dominant females were randomly distributed across patches in most experimental trials.

Social rank also affected an individual's feeding rate. Dominant males fed in a slow 'leisurely' fashion in almost all conditions, were unaffected to a great degree by the individuals around them, and showed little variation in their foraging returns across a wide range of conditions. In contrast, individuals of other social ranks fed much faster and showed more variation in their foraging returns, which were affected to varying degrees by interactions with other individuals around them.

Interference among foragers was an important underlying factor that drove the above patterns. The presence and distribution of subordinate classes were best explained as strategies of avoidance of adult males who engage in frequent and ritualized aggressions. In response to this, subordinate adult males avoided areas with dominant males, while sub-adults traveled in groups and aggregated in space, effectively reducing per-capita levels of aggression upon themselves. The behaviors of females as a class were more ambiguous and did not show easily discerned patterns. It is hypothesized that high levels of relatedness in this class skewed interference costs for this class in unknown ways.

A simple functional model for this system is proposed and it is shown that the relative importance of ecological versus social factors is mediated by social rank and interference.

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