Spatial variation in bird species abundances: Environmental constraints across southern Neotropical regions

Abstract

Climate and habitat type are frequently related with the abundance of individual species and have been hypothesized to be primary drivers of the spatial variation in species abundances at the regional scale. Our aim is to evaluate the relative roles of those environmental factors in determining spatial variation in bird species abundance. We surveyed birds and habitat-cover variables and compiled climatic data along a 1700-km latitudinal gradient in the southern Neotropics. To identify the primary environmental variable explaining spatial changes in species abundances we performed simple regressions; a goodness of fit test identified the environmental factor that most frequently acted as the primary predictor. Mantel tests and partial regressions were performed to account for the spatial structure of abundance and environmental factors and collinearity between them. Of the 88 species included, 70% responded primarily to habitat cover and the remaining to climate. Forest cover and annual thermal amplitude were the main habitat-cover and climatic variables, respectively, explaining spatial variation in bird abundances. Our results indicated that the considered environmental factors accounted for latitudinal changes in species abundances; however, habitat cover and climate together explained a higher proportion of the variation than each factor independently of each other. There was a primacy of habitat-cover type over climate to predict spatial changes in bird species abundances across the neotropical biogeographic regions studied, but the underlying causes are likely related with the interaction of both factors.