Document: PET-3-79-4

The importance of coupled variable recruitment and density dependence in the coexistence of coral reef fishes.

CHESSON, P.* ¹ and B.A.BYRNE ²

University of California Davis CA 95616 USA ¹
Oregon State University Corvallis OR 97331 USA ²

Abstract:
Coral reef fishes are known for their highly variable recruitment rates. Also, there is increasing evidence that density dependence may occur at a variety of stages in the life cycle, including mortality in early settlement, and growth of adults. These features were incorporated in a metapopulation model of reef fish communities, which showed that spatial and temporal variation in recruitment rates may strongly promote species coexistence when several conditions were satisfied. First, species should have different spatio-temporal patterns of recruitment so that the ratios of the recruitment rates of different species vary in space or time. Second, density dependence must be multispecies with both conspecific and heterospecific densities limiting population growth. Third, coupling between recruitment and density dependence must occur in the sense that density dependence must more strongly limit local population growth when local recruitment is high. Coexistence then occured even though species may differ, up to some maximum amount, in their fitnesses averaged over all environmental conditions. The maximum average fitness difference compatible with coexistence measured the strength by which coexistence was promoted. The strength of coexistence increased with the strength of the coupling between recruitment and density dependence. Moreover, the contribution of any stage in the life cycle to coexistence was diminished by density dependence at prior stages because the coupling of recruitment with density dependence at that stage was diminished by density dependence at prior stages. Density dependence in growth and reproduction may be poorly coupled with recruitment variation and therefore may only weakly affect species coexistence. An important exception was when there were large differences between average recruitment levels at different sites, in which case strong coupling between recruitment and density-dependent growth and reproduction developed over time, strongly promoting coexistence. This work emphasizes that recruitment limitation and density dependence should not be treated as alternative explanations for community structure. The interaction between the two is the dominant feature of coexistence in this model.

Keywords: recruitment, density dependence, coral reef fish, competition, predation, metapopulation, storage effect

This abstract is being presented at: 11:15 AM in session:
Oral Session #57: Ocean-Going Fish and Mammals.