Abstract
Artificial ponds or irrigated systems scattered throughout farmlands can offer important habitats for anurans and can be interesting sites for research on species resources use in a changing landscape. This study describes the diet and resource partitioning among anurans inhabiting irrigated rice fields in the Pantanal region. Twenty categories of prey were found in the stomachs of Leptodactylus chaquensis, L. elenae, L. podicipinus and Rhinella bergi, the most frequent being Coleoptera, Hymenoptera, larvae of Hexapoda, Hemiptera, Diptera and Orthoptera. The great differences found in the diet of these species in rice fields compared to other locations, according to available records in the literature, was the increased importance of Hemipitera and Orthoptera and the decrease in importance of Hymenoptera in the diet of leptodactylids. These differences might be attributed to changes in the availability of resources in response to habitat modification. Although diet composition was very similar among species, niche overlap was larger than expected by chance, suggesting that the competition for food resources is not, or has not been, a significant force in determining the structure of this frog community. Two non-exclusive hypotheses could be considered as a justification for this result: 1) the high niche overlap could result from resource availability, which is sufficient to satisfy all species without any strong competition; 2) or the high values of niche overlap could be a selective force driving species to compete, but there has not been enough time to express a significant divergence in the species diet because the study area is characterised as a dynamic habitat influenced by frequent and cyclical changes.
Highlights
Diet is an important life-history component of ecological niche
Assuming that in environments homogenised in response to human changes, competition for resources can be another force that drives the community to a diversity decrease, this study describes the diet of some of the most abundant frog species inhabiting irrigated rice fields in the Pantanal and measures the similarity and overlap in the use of food resources between species
Leptodactylus chaquensis exhibited the more diversified feeding habit (20 items) and was the only species to prey upon vertebrates
Summary
Diet is an important life-history component of ecological niche. Among anurans, community structure is often associated with a relationship between species habitat and diet (Duellman and Trueb, 1994). Aspects such as phylogeny, foraging mode, prey availability and abundance, and morphological constraints for capture and ingestion of a given prey type can be related to resource partitioning among species (Lima, 1998; Lima and Magnusson, 1998; França et al, 2004; Santos et al, 2004). Community niche differentiation can be influenced by human induced environmental changes, which may affect ecological interactions (Caldwell and Vitt, 1999; Albrech and Gotelli, 2001; Rocha et al, 2008)
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