Are primate folivores ecologically constrained? : a comparative analysis of behavioral indicators of within-group feeding competition
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Folivores do not exhibit a direct relationship between group size and daily path length and are consequently believed to experience little feeding competition. However, previous studies lacked sufficient control for ecological variation and did not account for the underlying hierarchical structure inherent in closely related taxa (phylogeny). The present analysis examined daily path length and relative ranging cost in 37 primate species, including 18 folivores, while controlling for ecological variation and phylogeny. Group size effects on group spread, changes in activity budget, and infant to female ratios were similarly investigated as these have been found to indicate feeding competition in folivorous primates. Although relative ranging cost was a not a significant predictor of folivore group size, large groups traveled significantly farther per day, increased group spread per individual, and had lower infant to female ratios than small groups. Large groups spent more time feeding and less time resting than small groups; however, these trends were not significant. A strong phylogenetic signal was detected among species’ mean values for average group size (λ = 0.827). Because primate group size and behavior represent the combination of adapting to present-day environments and phylogenetic inertia, future comparative analyses of feeding competition should account for both current ecological conditions and the phylogenetic signals inherent in the taxa being compared. As suggested by the current study, folivorous primates may utilize a number of foraging strategies, other than increasing daily path length, to alleviate feeding competition. To better assess feeding competition, future research should include alternative correlates of feeding competition such as increased group spread, changes in activity budgets, and decreased female fecundity. The information gained from such research may improve our current interpretations of the ‘folivore paradox’ and redefine the competitive regime of leaf eating primates.