Michelle
Brown
Ph.D. 2011
Assistant Professor,
Integrative Anthropological Sciences, UC Santa Barbara
website
Intergroup
encounters in grey-cheeked mangabeys (Lophocebus albigena) and redtail
monkeys (Cercopithecus ascanius): form and function
Dissertation Abstract:
Across species and populations, encounters between neighboring social
groups take a variety of forms. In particular, intergroup encounters
(IGEs) may or may not be aggressive and may include the participation
of males and/or females. The proximate causes of aggressive
participation by each sex, particularly among primates, is generally
thought to be the availability of mates and food. However, existing
hypotheses of resource defense have rarely been explicitly tested by
identifying the proximate causes of male and female aggression. In this
dissertation, I sought to test the existing hypotheses by determining
whether female food defense, male food defense, and male mate defense
occur in grey-cheeked mangabeys (Lophocebus albigena) and redtail
monkeys (Cercopithecus ascanius).
With a team of field
assistants, I observed six mangabey groups for 15 months and four
redtail groups for 12 months at the Ngogo site in Kibale National Park,
Uganda. We observed naturally-occurring IGEs in both species, simulated
IGEs among mangabey groups using playback experiments, and measured the
availability of food resources in botanical plots. I evaluated multiple
aspects of intergroup relations, including initiation of encounters,
occurrence of intense aggression, encounter outcomes, overall encounter
rates, and the effect of neighbors’ long-distance calls on group
movements. For each IGE aspect, I determined the effects of group size
and resource value.
I found evidence for female food defense
by redtails and male food defense by both species, and no evidence of
female food defense by mangabeys or male mate defense by either
species. In addition, the specific conditions under which food defense
is expected to occur in primates were appropriate for male mangabeys,
but not for female or male redtails. This pattern of results indicates
that existing hypotheses cannot accurately predict which populations
will exhibit food or mate defense by males or females, or the specific
social and ecological conditions that elicit defense. I also found that
mangabeys exhibited two types of IGE: whole group encounters, where the
majority of two groups were in visual contact, and subgroup encounters,
where one or a few individuals left their group and interacted
aggressively with a neighboring group. Whereas whole group IGEs
appeared to function as defense of specific feeding sites, subgroup
IGEs did not; instead, they appeared to be a means of defending the
core of the home range.
Compared to earlier studies, the
mangabey groups in this study exhibited higher rates of interaction and
more pronounced aggression. Higher group densities and more intense
feeding competition have given rise to a dramatically different pattern
of mangabey intergroup relations. This study demonstrates the
importance of considering multiple IGE aspects, hypotheses, and food
characteristics when evaluating the role of intergroup relations in the
lives of social animals.
After completing her PhD, Michelle was awarded an NSF Post-doctoral
Fellowship which she completed at the University of New Mexico. She
then joined the faculty at the University of California, Santa Barbara.
Publications based on doctoral research: (see also Michelle's web pages for more)
- Brown, M. 2014. Patch occupation time predicts responses by
grey‐cheeked mangabeys (Lophocebus albigena) to real and simulated
neighboring groups. International Journal of Primatology 35:491‐508, doi: 10.1007/s10764‐014‐9762‐8.
- Brown, M. 2013. Food and range defense in group‐living primates. Animal Behaviour 85:807‐816, doi: 10.1016/j.anbehav.2013.01.027.
- Brown, M. & Crofoot, M. 2013. Social and spatial relationships between primate groups. In: Primate Ecology and Conservation (pp. 151‐176). Eds: Sterling, E., Bynum, N., and Blair, M. Oxford University Press.
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