Niche Differentiation Data

Understanding variation in social grouping patterns among animal taxa is
an enduring goal of ethologists, who seek to evaluate the selective
pressures shaping the evolution of sociality. Cohesive association with
conspecifics increases intragroup feeding competition and is posited as an
important pressure affecting grouping patterns. Furthermore, in sexually
dimorphic species, males and females may have different nutritional
requirements, which may lead to suboptimal foraging in mixed-sex groups.
How do animals living in permanent social groups mitigate these foraging
costs? Niche differentiation is often hypothesized as a mechanism, but
rigorous and detailed tests of the extent and context of differences in
diet and habitat use, key tenets of this hypothesis, are rare. We
investigated the potential for niche differentiation in foraging activity
budget and environment use in a population of wild white-faced capuchin
monkeys ( Cebus imitator ) in northwestern Costa Rica. Using a robust
dataset of 15 879 foraging scan samples collected from 4 groups over 13
months, we found that smaller individuals - e.g. juveniles and females -
forage more often on smaller branches. We additionally found clear
evidence of predator sensitive foraging wherein the smallest individuals
spend less time on the ground during invertebrate foraging. Importantly,
niche differentiation was far more evident overall during invertebrate
foraging, likely due to spatial constraints and environmental homogeneity
imposed by fruit patches. In sum, we found considerable variation in
habitat use across age and sex classes, likely attributable to differences
in size and relative predation risk. These variables likely reduce
intraspecific feeding competition by promoting differential diet and
habitat use. Our results also provide insight into the limits of niche
differentiation as a strategy for competition reduction and may shed light
on the evolution of fission- fusion dynamics in highly frugivorous
species.