Null Models in Ecology

What determines the particular combinations of species found in biological communities, the number of those species, and their relative abundance? These questions are of perennial interest to ecologists, who often cite the influence of various factors-competition, predation, climate, nutrient availability, and chance dispersal events, to name a few. One way of testing hypotheses about the role of different processes is to search for patterns, i.e. similarities or differences between the compositions of speciflc communities. Process can be used to predict patterns, and pattern recognition can lead in turn to predictions about the consequences of experimentally manipulating natural communities. Such patterns typically involve: (a) some regularity in the relative abundance of species present in the community; (b) geographical correlates of the numbers of species; (c) the repeated occurrence or rarity of particular species or morphological combinations; and (d) differences in the behavior or morphology of a