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Portillo JTdM, Barbo FE, Azevedo JAR, Sawaya RJ.2018. Richness and phylogenetic diversity are affected by space and time in the megadiverse Atlantic Forest of South America. PeerJ Preprints6:e27450v1https://doi.org/10.7287/peerj.preprints.27450v1
Understanding variation of species richness along latitudinal gradients, with more species toward the tropics, represents a challenge for ecologists. Species richness also varies according to the available area, with more species in larger regions, with area and latitude posited as major drivers of richness variations. However, species richness does not fully capture the evolutionary history behind those patterns. Phylogenetic diversity can provide insights on the role of time and evolutionary drivers of environmental gradients. We analyzed here the latitudinal gradient of endemic snakes from the Atlantic Forest of South America, a megadiverse and highly threatened portion of the Neotropics. We assessed the effect of area and average clade age on species richness and phylogenetic diversity, testing whether species richness and phylogenetic diversity increase with area availability and in lower latitudes. We found that area can predict species richness, but not phylogenetic diversity. Brazilian southeastern mountain ranges include larger patches of Atlantic Forest and the highest richness levels, but generally harboring snakes from relatively recent clades (neoendemics). There is a negative relationship between species richness and average clade age along the latitudinal gradient, with older clades found mainly in northern portions, increasing phylogenetic diversity at lower latitudes. Different dimensions of diversity, species richness and phylogenetic diversity, are thus affected in different ways by area and time for speciation in the Atlantic Forest, and this may be a trend in highly diverse tropical regions.
Our research article contributes to better understand the distribution of endemic snakes from one of the most highly threatened hotspot of the Neotropical region, the South American Atlantic Rainforest. We analyzed how richness and phylogenetic diversity are distributed regarding to the geographical extent variation, latitude and the time-for-speciation effect. In this way, we discuss how ecological and evolutionary factors interact with the exclusive snake diversity from the Atlantic Forest. Our findings shed light to comprehend different mechanisms for different diversity metrics along the latitudinal gradient in Atlantic Forest. This snakes example provides better understand for the biodiversity distribution patterns, discussing interesting issues into the ecology, biogeography and evolutionary biology.