Are there shared general patterns of specific diversity, abundance, and guild structure in snake communities of tropical forests of Madagascar and continental Africa?

A comparative study of snake community composition of 45 tropical forest patches, including both original and literature data, is presented. Twelve study areas are situated in Nigeria, one in Cameroon, and 30 in Madagascar. Two forest sites from Panama were also used as outgroups. There was a remarkable consistency among: sites in inter-regional comparisons in terms of mean number of species observed x min. The highest similarities were between Nigerian and Malagasy sites and between Cameroon and Nigerian sites, whereas similarities between all these African sites and Panama sites were lower. Altitude and linear distances among sites did not influence significantly the snake species detection and abundance. Nigerian sites had comparatively higher numbers of semi-aquatic taxa than Malagasy sites. The terrestrial guild was the dominant one, and the arboreal guild was constituted by a remarkable diversity of species, in nearly all sites of both Nigeria and Madagascar. There was a very low diversity of syntopic fossorial species in both Nigeria and Madagascar (in all 22 study plots, only 1 or 2 fossorial species were found). In Nigerian sites there was a general prevalence of primarily lacertophagous and mammalophagous species, but batracophagous and ornithophagous species were also quite abundant. In the Malagasy sites lacertophagous species were significantly prevalent, followed by batracophagous species, whereas species with other dietary preferences (e.g., mammalophagous) were much under-represented. The abundance of species feeding: on invertebrates and of generalist species was similar in the two geographic regions, whereas piscivorous species were found only in the Nigerian sites. The scarcity of mammalophagous, piscivorous and ornithophagous species in Madagascar could be interpreted as a general biogeographic pattern in terms of food type availability (taking into account the scarcity of some types of prey in Malagasy forests and freshwater streams) as well as in terms of snake size distributions. With regard to snake body size distributions in the various examined communities, it appeared that forest environments of both Nigeria and Madagascar can house a similar snake community as for numbers of species < 2 m in length, but Nigerian environments can harbour numbers of giant and very large species (from 2 to 9 m in length) that cannot be hold in Malagasy forests. The ecological patterns emerged in this comparative study are discussed in the light of current community ecology theory and biogeography.