Seasonal patterns of abundance and recruitment in an amphibian assemblage from the Paraná river floodplain

Abstract

"The seasonality of amphibian activity is a long studied and recognized feature but generally includes only the analysis of adult calling males. In this study, seasonal variation in abundance of a whole assemblage (adults and juveniles), coexistence patterns and phenology were analyzed in a community of 16 amphibian species inhabiting lowland river floodplain ponds. Species activity period was wider than reproductive phase and assemblage activity concentrated in the warm season. The seasonal patterns of abundance and population size structure varied among species but nestedness structure and positive co-occurrence was found for adults and juveniles assemblages. Most adult hylids are characterized by prolonged activity periods while bufonids, cycloramphids, leiuperids, leptodactylids and microhylids varied from prolonged to explosive. Recruitment of juveniles was intensive or explosive in nine out of ten evaluated species, generating a seasonal reduction in population size structure. The gathered recruitment indicates that warm season is particularly favorable for ingress of juveniles to populations. River hydrometric level was the best predictor of anuran activity, although seasonality (temperature and photoperiod), humidity and rainfall also were informative. The slight differences in activity patterns with respect to other studies could be attributed to variations in local factors and differences in habitat seasonality. Since the studied amphibians utilize the same habitat, activity and recruitment differences among species should be the consequence of combined effects of evolutionary fixed life history traits and present ecological interactions. Thus, there is a mixture of profound and proximate factors ruling species activity and seasonal changes in assemblage structure."