SPATIAL VARIATION IN BAT SPECIES RICHNESS IN A FOREST-GRASSLAND TRANSITIONAL REGION OF SOUTHEASTERN SOUTH AMERICA

Abstract

The latitudinal diversity gradient is the most well-known ecological pattern. Several hypotheses have been proposed to explain this biodiversity gradient. However, the predictors of species richness at continental scales may have different effects at regional scales, and even lose importance. Here we tested the effects of climate, energy, and habitat heterogeneity on the spatial variation of bat species richness in a forest-grassland transitional region, in southeastern South America. Our main goals were to assess which variables better explain bat species richness, and to analyze redundancy and complementarity among hypotheses. We generated three regression models, being each model related to a hypothesis, and compared R-squared among models. Then, we estimated redundancy and complementarity among hypotheses by partitioning the variation in species richness into unique and shared effects among hypotheses. Climate explained a larger proportion of the spatial variation of bat species (R² = 0.97, p < 0.0001), followed by heterogeneity (R² = 0.94, p < 0.0001), and energy (R² = 0.93, p < 0.0001), respectively. Variation partitioning analysis showed that climate explained the largest proportion of richness variation (83%). Energy and heterogeneity explained 55% and 51% of bat richness, respectively. The amount of variation explained uniquely by climate and heterogeneity were identical (R² = 0.09) whereas energy explained a small fraction of the variation (R² < 0.01). We conclude that climatic conditions coupled with habitat heterogeneity were the main predictors of bat richness in a forest-grassland transitional region and that the variables explaining regional richness gradient were the same at continental scale.