Epsilon Open Archive

Abstract

The various features determining species distributions remain enigmatic in ecology. This thesis deals with the spatial and temporal dynamics of land birds on the islands of the Dahlak archipelago, the Red Sea, and of mammals, birds and reptiles among the forest fragments of the archipelago-like east African coastal forest. The bird species richness on the islands of the Dahlak archipelago depended on area, isolation and extent of habitat. Similarly, species richness of the east African forest fragments was related to area, habitat diversity and isolation but the importance of each factor varied among taxa as well as among generalists and specialists. For example, area influenced species richness of most categories except specialist mammals and reptiles, habitat diversity was more important for forest specialists than generalists, and isolation was important only for birds. In both study areas, similarity in bird species composition decreased with increasing distances among isolates suggesting that dispersal from source pools and among isolates facilitate re-colonization. The nested community structure, i.e. species composition of species−poor communities are a subset of species−rich communities, of birds in the Dahlak archipelago depended on area and the distribution of a few habitats. Similarities in community patterns and cooccurrence patterns, at both community and species levels, were mainly related to habitat preferences and corresponding distributions of habitats as well as inter-island distances. Also, the distributional patterns suggest that predator-prey interactions can be a determinant of the spatial distribution of, at least, the prey. There was no evidence of competitive exclusion. The nested structure on the islands of the Dahlak archipelago remained fairly stable over a period of 35 years even in this arid region. The turnover dynamics were broadly predictable from the nested pattern but not always consistent with other expectations from nested community structure. Taken together my results show that mechanisms on varying spatial and temporal scales act on species distributions, and that the influence may vary among taxa mainly depending on dispersal ability. In the case of conservation, comprehensive strategies accounting for these variations are needed.