Population Variation in a Tropical Bird Community

Abstract

B ird communities in tropical forest are tremendously diverse relative to those in temperate forests; more species have been reported from Costa Rica than from all of North America (Stiles et al. 1989). Similarly, approximately the same number of species (400-410) have been recorded from La Selva Biological Station, a 15-square-kilometer wet forest site in Costa Rica, as from the entire state of Missouri (Blake et al. 1990, Robbins and Easterla 1992). Species diversity is even greater in parts of South America: territories of more than 160 species overlap at a single point in forest in Peru (Terborgh et al. 1990). Many factors contribute to the greater diversity of tropical forest bird communities (Terborgh 1980), including the year-round availability of certain resources (e.g., flowers and fruits) that are rare in temperate habitats (Karr 1971, Orians 1969). Whereas the number of species is much greater in tropical rather than in temperate habitats, the total density of birds does not differ, Terborgh and his colleagues (1990) concluded from one of the most detailed comparisons between temperate and tropical bird communities (see also Thiollay 1990). The relationship occurs primarily because many tropical species are relatively rare (Karr 1990a). Total biomass of birds, however, can be