Opposite latitudinal gradients for species richness and phylogenetic diversity of endemic snakes in the Atlantic Forest

The decrease in species richness toward higher latitudes is an expected biogeographical pattern.This pattern could be related to particular envi-ronmental constraints and the evolutionary history of clades.However,species richness does not fully represent the evolutionary history of the clades behind their distributions.Phylogenetic diversity better clarifies the role of historical factors in biogeographical patterns.We analyzed envi-ronmental and historical drivers related to latitudinal variation in species richness and phylogenetic diversity of Atlantic Forest endemic snakes.We implemented species distribution models,from voucherbased locality points,to map the snake ranges and diversity.We used generalized additive mixed models to evaluate the relationships among the diversity metrics and area,topographical roughness,and past climate change velocity since the Last Maximum Glacial in the Atlantic Forest latitudinal gradient.Contrary to the expected general pattern,species richness was higher toward higher latitudes,being positively related to past climatic stability.Species richness also increased with total area and higher topographical roughness.Phylogenetic diversity,on the other hand,showed opposite relationships related to the same factors.Phylogenetic diversity increased with lower climatic stability in lower latitudes.Thus,dimensions of diversity were affected in different ways by historical and environmental constraints in this unique and threatened biodiversity hotspot.

Climatic niche breadths of the Atlantic Forest snakes do not increase with increasing latitude

The climatic niche is a central concept for understanding species distribution,with current and past climate interpreted as strong drivers of present and historical-geographical ranges.Our aim is to understand whether Atlantic Forest snakes follow the general geographical pattern of increasing species climatic niche breadths with increasing latitude.We also tested if there is a tradeoff between temperature and precipitation niche breadths of species in order to understand if species with larger breadths of one niche dimension have stronger dispersal constraints by the other due to narrower niche breadths.Niche breadths were calculated by the subtraction of maximal and minimal values of temperature and precipitation across species ranges.We implemented Phylogenetic Generalized Least Squares to measure the relationship between temperature and precipitation niche breadths and latitude.We also tested phylogenetic signals by Lambda statistics to analyze the degree of phylogenetic niche conservatism to both niche dimensions.Temperature niche breadths were not related to latitude.Precipitation niche breadths decreased with increasing latitude and presented a high phylogenetic signal,that is,significant phylogenetic niche conservatism.We rejected the tradeoff hypotheses of temperature and precipitation niche breadths.Our results also indicate that precipitation should be an important ecological constraint affecting the geographical distribution of snake lineages across the South American Atlantic Forest.We then provide a general view of how phylogenetic niche conservatism could impact the patterns of latitudinal variation of climatic niches across this biodiversity hotspot.