PATTERNS OF SPECIES AND COMMUNITY DISTRIBUTIONS RELATED TO ENVIRONMENTAL GRADIENTS IN AN ARID TROPICAL ECOSYSTEM

The heterogeneous vegetation mosaic of the South Turkana region of nor th Kenya is associated with diversity in the region's physical environ ment. The abundance and distribution of the dominant species are relat ed to gradients in those abiotic factors that influence water availabi lity, including precipitation, soil texture, and topographic relief. R esearch focused on three Acacia species that are a major component of the Turkana vegetation; A. tortilis, A. senegal, and A. reficiens. The se species each exhibit a different response to variations in abiotic factors. Consequently, species abundance varies independently across t he landscape, creating a continuum of intergrading populations. Commun ity types can be identified within the mosaic of intergrading populati ons. Although community borders are not discrete due to continual chan ge in species abundance, types are identifiable and are repeated in ar eas with similar environmental conditions. The landscape patterns are representative of Whittaker's (1953) climax-as-pattern, with communiti es created by individual patterns of populations responding to environ mental gradients, creating a continuum of community change across the landscape.