Patterns of species richness and compositional similarity of vertebrate fauna of east African coastal forests: a comparative analysis of birds, mammals, and reptiles
Azeria, E.T.; Sanmartin, I.; As, S.; Carlson, A.
Acta Universitatis Agriculturae Sueciae Silvestria 311: 1-22
Aim - To examine ecological determinants of species richness and compositional similarity of groups of vertebrates with contrasting dispersal ability and forest dependence across an archipelago-like distribution of forests Location - East Africa coastal forests within Swahili regional centre of endemism and the Swahili-Maputaland regional transition zone Methods- The most recent data on species distribution of birds, mammals and reptiles was taken from published work. Analysis of ecological determinants of species richness includes forest area, isolation, altitude both median and range. Cluster analysis and Parsimony analysis of distribution (PAD) were carried to find cladograms depicting the relationships of the fauna between the coastal forests. We use mantel test of composition similarity vs. inter-forest distances to explore the geographical correspondence of the distribution patterns of the vertebrate communities. Results - Bird species richness of both forest generalist and specialist birds increased with area and decreased with isolation. Species richness of specialists was positively correlated to altitude range, and that of generalists also to the median. Species richness of mammals was positively correlated to altitude range, where as forest generalists with area. Species richness of specialist reptiles was related to both range and median altitude of forests, and separate analyses showed 'coastal endemics' increased with altitude range, where as that of 'forest endemics' with median altitude. None of the mammals or reptiles species richness responded to isolation. The cladograms from PAD and cluster analysis of bird distribution showed groups with geographical and ecological correspondence. Similarly mantel test showed compositional similarity of bird communities between forests decreased with increasing inter-forest distance. Compositional similarity of mammals between the forests did not show strong geographical correspondence, but in few smaller subgroups. Cladogram based on reptiles was not resolved, and generally with low similarity levels. A few two-area groups corresponded to geographical location. Conclusion - We suggest variation in the response of the faunal groups to forest attributes are related to differences in life history traits, i.e. dispersal ability and/or habitat specialization. Dispersal between forests might be common among birds, but not in mammals and reptiles. Forest diversity, associated to altitude range, may be important for forest specialist birds, mammals and 'coastal endemics' than for non-specialists. Present distribution of 'forest endemic' may be relicts that survived forest area contraction and tidal inundations, on higher laying forests. Parsimony analysis based on birds and mammals showed biogeographical affinities that signal current and historical ecological phenomenon. Moreover, it was congruent with some of general classification areas of endemism adopted for this area.