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.

Community composition and an index of relative abundance were analyzed for mammals (excluding most rodents, shrews and bats) of five forest reserves in the Niger Delta (Southern Nigeria). Twenty-nine species were recorded, 86.2% of them being found in all protected areas. Although most of the species were already known from the study area, there were unexpected patterns concerning the duikers. Indeed, the presence of only one species (Philantomba walteri) (CH Smith, 1827) was confirmed, whereas at least five additional duiker species were reported for the study area by earlier authorities. Another duiker species (Cephalophus niger Gray, 1846) was recorded once during the present surveys and is not known whether it represents a stabilized presence in the Niger Delta. The empirical Abundance Index suggested that only three species were very rare (Trichechus senegalensis (Link, 1795), C. niger, and Pan troglodytes (Blumenbach, 1775)). Diversity-dominance diagrams showed that the evenness profiles were similar across study areas. Linear distance (Km) between the barycenters of forest reserves was significantly positively correlated with relative community composition dissimilarity. Overall, a biotic homogenization process for the mammal communities of the five forest reserves was observed, likely as an outcome of the high deforestation of the last 50 years.

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