Dry season resources and their relationship with owl monkey (Aotus azarae) feeding behavior, demography and life-history

Abstract

Limited food resource availability during yearly dry seasons can influence population dynamics and direct life-history evolution. We examined actual food production during two dry seasons and its relationship to feeding, life history, and demography in territorial, monogamous, and pair-living owl monkeys (Aotus azarae azarae). To quantify food availability in 16.25 ha of gallery forest in the Argentinean Chaco, we collected phenological data, from dry season fruit sources (N=894), twice a month, during July and August of 2008 and 2009. At the same time, we collected feeding data from the four groups (N=1448 h) inhabiting that forest portion. We also examined demographic data on births, natal dispersal, and group size. Our data show that owl monkeys occupy territories, and core areas, that produce food consistently, even during harsh times. Following the 2009 drought, less fruit was available than in 2008, but the 50 % core areas produced fruit amounts comparable to the 80 % territories. Owl monkeys showed dietary flexibility; fruits were the most frequent food item in 2008, whereas all groups increased their consumption of leaves in 2009. Infant production was lower in 2008 than after the drought of 2009. Interbirth intervals between the 2 yr were longer than the mean for the population, and more individuals dispersed in 2008 than in 2009. Our study suggests that owl monkeys occupy territories that provide similar amounts of reliable dry season foods within the core areas. Although access to these core areasmay allow themto overcome severe dry seasons, our findings underscored the difficulties of understanding the potential causal relationships between ecological factors and demographic and life-history parameters.