Factors Affecting the Population Dynamics of Two Toads (Anura: Bufonidae) in a Seasonal Neotropical Savanna

Abstract

We studied the population dynamics of Bufo schneideri and B. rubescens during three years in the Cerrado biome of central Brazil. Using mark–recapture models, we estimated demographic parameters and evaluated the effects of sex and climate upon them. We used model selection, based on the Akaike's information criterion (AICc), to test hypotheses of variation in demographic parameters. The adult sex ratio was male-biased for both species, and breeding took place in the dry season for B. rubescens and in the transition from dry to wet season for B. schneideri. There was no difference in recapture probability between sexes, but there was significant variation among months. Recapture probability was associated with rainfall and temperature of the previous month in B. rubescens, but had constant values for the same months in different years in B. schneideri, showing a cyclic seasonal pattern. Survival estimates were constant in time and no significant difference was found between sexes in both species. Annual survival was 0.35 for females and 0.37 for males of B. schneideri, and 0.34 for males and 0.38 for females of B. rubescens. We found no evidence for temporary emigration in both populations, but the presence of transients was significant. For both species, adult population size was moderate, with larger values during the breeding season. The similar demography of B. rubescens and B. schneideri illustrates the high ecological and morphological conservatism reported in the genus Bufo.