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Individual variation in resource use by opossums leading to nested fruit consumption

Authors


M. Cantor, Dept. Ecologia e Zoologia, Univ. Federal de Santa Catarina, CEP 88040-970, Florianópolis, Brazil. E-mail: m.cantor@ymail.com

Abstract

Despite recent findings on the ecological relevance of within population diet variation far less attention has been devoted to the role diet variation for ecological services. Seed dispersal is a key ecological service, affecting plant fitness and regeneration based on foraging by fruit-eating vertebrates. Here we used a network approach, widely used to understand how seed-dispersal is organized at the species level, to gain insights into the patterns that emerge at the individual-level. We studied the individual fruit consumption behavior of a South American didelphid Didelphis albiventris, during the cool–dry and warm–wet seasons. In species–species networks the heterogeneity in specialization levels generates patterns such as nestedness and asymmetry. Because generalist populations may be comprised of specialized individuals, we hypo thesized that network structural properties, such as nestedness, should also emerge at the individual level. We detected variation in fruit consumption that was not related to resource availability, ontogenetic or sexual factors or sampling biases. Such variation resulted in the structural patterns often found in species–species seed-dispersal networks: low connectance, a high degree of nestedness and the absence of modules. Moreover structure varied between the warm–wet and cool–dry seasons, presumably as a consequence of seasonal fluctuation in fruit availability. Our findings suggest individuals may differ in selectivity causing asymmetries in seed dispersal efficiency within the population. In this sense the realized dispersal would differ from the expected dispersal estimated from their average dispersal potential. Additionally the results suggest possible frequency-dependent effects on seed dispersal that might affect individual plant performance and plant community composition.

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