Untangling the imprints of climate, geography and land use/cover on bird diversity in the South American Gran Chaco

Aim: To evaluate the structure of bird communities throughout the South American Gran Chaco determining the effects of climate, geography, and land use/land cover in bird beta diversity, as well as to understand the beta-diversity processes underlying land-use changes across broad spatial ranges. Taxon: Birds. Location: South American Gran Chaco. Methods: We constructed a site-by-species matrix with occurrence probabilities of 293 bird species across 2669 spatial units tiling completely the study area. Based on this matrix, we calculated pairwise dissimilarities scores and performed a hierarchical cluster analysis for describing the spatial configuration of dissimilarities. The clustering result was spatially represented through an original venation map with boundaries between sites widened in the function of their distance in the dendrogram. We used the Generalized Dissimilarity Modelling approach to model beta diversity, using geographic distance, climatic and land use/land cover information as predictors. We mapped beta-diversity patterns using color theory and the HSV color model. Results: We identified two main clusters of sites across the Gran Chaco, which represent environmentally different sites and harbour very distinct assemblages of species. These main groups are separated by two natural delimiters: The Bermejo-Pilcomayo interfluvium and the Lower Paraná floodplain. Overall, we observed that the percentage of cropland and climatic variables were important shapers of bird beta diversity. Main conclusions: We provide the first area-wide assessment of land use/land cover effects on bird beta diversity for the Gran Chaco. The distribution of croplands has a marked influence on bird beta diversity at regional scale highlighting the role of anthropic changes in reshaping bird beta diversity within the ecoregion. Taking into account the global increasing conversion of forests into croplands, a growing footprint of land use changes over geographical patterns of bird diversity in forest biomes can be anticipated