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Understanding large- and small-scale patterns and the determinants of species richness is central for the study of evolutionary mechanisms. The extent to which species richness in local communities is related to larger-scale processes is a pre-eminent topic in ecological and evolutionary research. To investigate how local and regional species richness are related, we sampled freshwater turtle assemblages in seven localities to represent the variation in ecological conditions along a 90 km south–north megatransect in Benin, West Africa. In each locality, all turtles captured were identified and measured, and the microhabitat in which individual turtles were observed was classified. Based on these data, we used community diversity metrics to compare turtle assemblages. Spatial autocorrelation did not affect our data. For all localities pooled, two species (Pelusios castaneus and Pelomedusa olivacea) were the most common and one species (Trionyx triunguis) was the rarest. Analyses of the commonest and more numerous species showed that the abundance of Pelusios castaneus declined with an increase in latitude and longitude, but the opposite was true for Pelomedusa olivacea. We showed that various characteristics of the microhabitat were significantly correlated with the abundance of the two common species. We found significant but variable south–north gradients in microhabitat use for different turtle species. Our results highlight the importance of studying interactions between local environments, the ecological requirements of each species and their synecological relationships. [ABSTRACT FROM AUTHOR]

The diet composition of rainbow lizards (Agama agama complex) populations was studied by feces analysis at eight distant places across a mega-transect in the Gulf of Guinea (West Africa), covering three countries: Togo, Benin and Nigeria. The effects of geography (= linear distance between study sites) and local conditions (using the mean annual rainfall as a proxy of the site-specific conditions) on dietary similarity of rainbow lizards were tested. Rainbow lizards were mainly insectivorous at all sites. Multivariate analyses identified four main groups of localities in terms of diet diversity indexes, with populations inhabiting forest towns tending to have less prey taxa richness than conspecifics from more arid areas, which instead had higher dietary evenness. Food niche overlap between populations was high among populations (range 0.631-0.940, x = 0.839), and decreased with increases in the difference of mean annual rainfall between sites. There was no effect of the geographic distance on the similarity in diet composition between populations. A UPGMA dendrogram revealed a geographic trend in terms of presence/absence of the various prey types in the diets, with all the Nigerian study sites forming one cluster, whereas Lomé and Cotonou, two cities situated within the Dahomey Gap, being grouped apart. Overall, rainfall of the various sites seems to be more important than geographic distance for determining the taxonomic diet composition similarity of these lizards. [ABSTRACT FROM AUTHOR]