Factors contributing to non-randomness in species Co-occurrences on Islands.

There has been dispute whether patterns of species co-occurrence on islands are largely random. We present a new method for testing this question; this method lets one not only examine whether a whole fauna is non-randomly structured, but also identify in which direction and by how much each particular species combination deviates from expectations based on randomness. Application of this method to the whole Bismarck and New Hebridean avifaunas, and to two particular guilds, shows that some pairs of species have more exclusive distributions than expected for random placement of species, because of competition, differing distributional strategies, or different geographical orgins.

Examination of the "null" model of connor and simberloff for species co-occurrences on Islands.

Among birds of the Bismarck Archipelago, only certain combinations of the species in a guild coexist on islands, and some species that are very similar ecologically have mutually exclusive distributions. Diamond (1975) interpreted these patterns as biologically significant, involving effects such as competition. Connor and Simberloff (1979) claimed such patterns to be not recognizably different from random, because they were scarcely distinguishable from those generated by a "null" distribution supposedly not incorporating competition.

Asymmetries in population growth regulated by intraspecific competition: Empirical studies and model tests.

The linearity assumption in the logistic model of population growth is violated for nearly all organisms. Two simple models, the θ-logistic and the θ-Ricker, are shown to account for asymmetric patterns of population growth for 27 species of Drosophila and for a variety of other organisms, where the data were derived from the literature. These models are developed so as to aid laboratory and field ecologists to anticipate the dynamics of various experimental organisms.