Uso do microhábitat e variação sazonal em uma comunidade de girinos : um estudo de caso no Pampa Brasileiro

Abstract

The intrinsic variability (population cycles and resources) and extrinsic (spatial and temporal heterogeneity) are considered determinants of dynamics, interactions, and patterns species coexistence. In the present study we determined the degree of overlap in microhabitat use by tadpoles in a semi permanent pond located in the Serra do Sudeste region, Rio Grande do Sul state, and we tested the influence of environmental descriptors as predictors of species micro distribution over time. Tadpoles were sampled with metal tube of 1.12m height and 0.27m of diameter, along the four annual seasons, in different microhabitats available (20 samples per season). We used a null model to determine if the community was competitively structured and use ANOSIM (analysis of similarity) to test whether the community structure differed among seasons, as well as we used Redundancy Analysis to determine the influence of environmental descriptors on the spatial distribution of tadpoles. We recorded 15 species, distributed in four families. Niche overlap was lesser than expected by chance and negatively related to species richness recorded along the year seasons, suggesting structuring by competition. ANOSIM showed differences in community structure between the four seasons, with less differentiation between autumn and winter seasons. Environmental descriptors that best explained the distribution of anuran species in the summer and spring were edge distance and water depth; in the spring water temperature also was important. None of the descriptors explained micro distribution of species in autumn and winter seasons. Here we indicate that interspecific competition seems an important determinant of spatial micro distribution of tadpoles, but that organization of larval community was temporally dynamic. Furthermore, we find indications that a mechanism of narrowing niche acts as moderator of tadpole microspatial overlap, which is important to explain the species coexistence along the time.