Aggregation does prevent competitive exclusion: A response to Green

Shorrocks, Bryan and Rosewell, Jonathan (1988). Aggregation does prevent competitive exclusion: A response to Green. American Naturalist, 131(5) pp. 765–771.



Green (1986) raised a number of points concerning our simulation model of competition on a divided and ephemeral resource (Atkinson and Shorrocks 1981; Shorrocks et al. 1984), its analytical counterpart (Ives and May 1985), and the review of possible mechanisms giving rise to aggregation (Atkinson and Shorrocks 1984). This model allows a competitively inferior species to survive in probability refuges, that is, sites with no or few superior competitors that arise as a result of an aggregated distribution of individuals over breeding sites. Such refuges may occur even at equilibrium density, since aggregation increases crowding (Lloyd 1967), and global population density is limited by strong intraspecific competition in sites with high local density while low-density sites still exist. The model developed from field studies of drosophilid flies (Atkinson and Shorrocks 1977; Shorrocks 1982; Shorrocks and Rosewell 1987).

In particular, Green's criticisms make use of the suggestion by Atkinson and Shorrocks (1984) that the observed negative-binomial distributions of drosophilid eggs over breeding sites could arise from a Poisson distribution of egg-laying visits by females to breeding sites, where eggs are laid in clutches, the size of which has a logarithmic distribution.

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