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.