Seasonality in anuran activity and calling season in a Brazilian subtemperate wetland

Background: Most tropical regions have a climate characterized by marked seasonal rainfall patterns, and these seasonal patterns of rainfall directly affect anuran activity. However, in regions with temperate climates, the main aspect of climate related to anuran activity is the thermal regime. Thus, transitional climate regions represent good opportunities to study the effect of abiotic factors on anuran activity. In this study, we present new data on the activity pattern and calling season of Neotropical anurans in a subtemperate climate. Anuran activity was assessed based on the rate of capture of specimens in pitfall traps and calling surveys. The field study was conducted between May 2010 and April 2011 in wetlands in southernmost Brazil. Results: An analysis based on directional (circular) statistics showed that general activity in the studied anurans was significantly seasonal. In addition, the general activity pattern of most species was regulated by temperature, not by rainfall, and approached that observed in regions with a temperate climate. However, we did not record a well-defined peak in the number of species displaying calling activity. This parameter did not exhibit any influence of temperature variations or rainfall. Conclusions: The observed general activity pattern is different from that expected for the majority of anurans inhabiting eastern South America. The present study showed that the general activity patterns of most anurans in the wetland region in southernmost Brazil are regulated by temperature and not rainfall, similar to the pattern of anuran assemblies from temperate climates. However, the nonexistence of a significant relationship between calling activity and any of the environmental variables tested suggests the presence of a different environmental factor (e.g., photoperiod or the length of the hydroperiod of the relevant water bodies) as a trigger for the levels of general calling activity.