Within‐ and Between‐Habitat Avian Diversity in African and Neotropical Lowland Habitats

The general pattern of changes in avian communities along latitudinal, successional, or moisture gradients have been clarified in recent years. However, few studies have compared avifaunas of similar vegetation types and climates in two tropical regions. In this study I asked two questions. How similar ecologically are the avian communities in two tropical areas (Panama and Liberia) with similar climate? To what extent might differences be due to historical factors? In general, there is convergence in the structural and functional characteristics of species and communities in the two tropical regions. However, because historical factors have been different in detail, avifaunas of varying faunal complexity have developed. The forest fauna of Panama is richer than that of Africa but the situation is reversed in grassland and savanna. This seems to be due to the geographic extent of these habitats and their degree of fragmentation during the Pleistocene. Food and habitat specializations are more striking in the neotropics than in Africa. In addition, several feeding guilds, especially bark—gleaners, hover—gleaners, and salliers, are less well represented in Africa. A lower number of bird species feeding on fruit and flower resources in Africa parallels a similar trend in bat communities. The reasons for these differences are complex and outweigh the trends toward convergent evolution in areas of similar climate. Differences of historical geography in the two regions are correlated with the differences in the two avifaunas. These include long— and short—term effects of weather and climate, differences in distribution and abundance of dispersal barriers, trophic role replacements, variation in coevolutionary interactions among groups, and varying histories of human influence. In brief, it appears that the avifaunas of Central America and Africa would be more similar if (1) there were fewer isolating barriers (especially mountains and rivers) in South America, (2) Central America were more isolated from the barriers and consequent high speciation rates of South America, (3) man's influence had been of longer duration in Central America, and (4) the Central American dry season was longer and/or less predictable. These factors and their interactions have produced faunas that are clearly tropical but which are different in a number of respects.