Abstract
The study of the feeding ecology of amphibians is an old issue in herpetology. Notwithstanding, the lack of food resources data in many studies of amphibians feeding has lead to partial understanding of frog feeding strategies. In this study we evaluate the trophic selectivity of a red spotted green frog (Hypsiboas punctatus) population from a Middle Paraná River floodplain pond in Argentina, and discuss the importance of prey availability data when interpreting results from diet analysis. We analyzed the gut contents of 47 H. punctatus adults and compared frog's diet with the environmental food resources. Prey availability was estimated by systematically seep-netting the microhabitat where anurans were localized foraging. We identified 33 taxonomic categories from gastrointestinal contents. Numerically, the most important prey categories were dipterans, followed by hemipterans, homopterans and coleopterans. The diet similarity between males and females was high and no statistical differences in diet composition were found. The most abundant food resources in the environment were dipterans, coleopterans, homopterans and collembolans. In order to assess whether frogs were selecting their preys, we calculated Pianka's niche overlap index and Jacobs' electivity index comparing gut contents to prey availability data. Trophic niche overlap was medium but significantly higher than expected by chance. The electivity index indicated that H. punctatus foraged dipterans slightly above their environmental abundance. Among the secondary preys, hemipterans were foraged selectively, homopterans were consumed in the same proportion to their occurrence in the environment, coleopterans were foraged quite under their availability and collembolans were practically ignored by frogs. Without food resources data, H. punctatus could be classified as a specialist feeder, but dipterans also were quite abundant in the environment. Our results show that H. punctatus fit better as a generalist feeder, foraging on their main food item and some secondary preys in similar proportion to their environmental availability; even though other secondary preys are being selectively preferred or ignored by frogs. Our data illustrate the importance of including the resource availability data on diet studies to improve the understanding of amphibian feeding ecology.
Highlights
Amphibian feeding ecology analysis has been carried out based on taxonomic identification of gut contents (Frost 1935, Klimstra & Meyers 1965, Lajmanovich 1995, Caldwell & Vitt 1999, Parmelee 1999, Maneyro et al 2004, López et al 2005b)
Feeding habits are an old subject in amphibian natural history studies (Frost 1924, 1935, Hamilton 1930, 1948, Cott 1932, 1934, Korschgen & Moyle 1955), the analysis of environmental prey availability for a better understanding of feeding ecology of this group was recently incorporated on batrachological studies (Hirai & Matsui 2000b, 2001a, Isacch & Barg 2002, Hirai 2004, López et al 2007)
The purpose of this study is to describe the diet, compare it to the environmental food resources, and evaluate the trophic selectivity of a H. punctatus population inhabiting a fluvial pond of middle Paraná River in Argentina
Summary
Amphibian feeding ecology analysis has been carried out based on taxonomic identification of gut contents (Frost 1935, Klimstra & Meyers 1965, Lajmanovich 1995, Caldwell & Vitt 1999, Parmelee 1999, Maneyro et al 2004, López et al 2005b). Hypsiboas punctatus is a widely distributed Neotropical hylid frog (total range area = 11 306 927km2) This species occurs throughout the Amazon basin in South America, south to the Chaco region of Paraguay and along the banks of the Paraguay-Paraná Rivers in Argentina. Gallardo & Varela de Olmedo (1992) discussed some aspects of the ecology of H. punctatus, there is only one analysis of the diet of this frog for the Paraná River environments (López et al 2002) In this short communication, López et al (2002) reported a high proportion of dipterans (over 50%) in H. punctatus gut contents but suggested a “sit and wait” foraging behaviour for this species without assessing frogs food selection. The purpose of this study is to describe the diet, compare it to the environmental food resources, and evaluate the trophic selectivity of a H. punctatus population inhabiting a fluvial pond of middle Paraná River in Argentina
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