Document: ERI-3-92-13

Intrametapopulation competition: Implications for population and metapopulation persistence.

BJORKSTEDT, E.P.*

National Marine Fisheries Service, SWFSC, Santa Cruz/Tiburon Lab, Tiburon, CA 94920 USA ¹

Abstract:
Theory for metapopulation dynamics typically assumes that interaction between subpopulations occurs solely through dispersal. However, for species in which the life-cycle consists of several stages that occupy different habitats, subpopulations may experience density-dependent dynamics, such as competition, in common habitats. One case where this may occur is in metapopulations of anadromous salmonids in which individuals from geographically and temporally distinct spawning populations aggregate and interact over increasing spatial scales in common freshwater migration corridors and marine habitats during the course of the life cycle. Classical dispersal between populations in these metapopulations occurs as maturing adults return to spawning habitats other than that in which they were born. I develop analytical, numerical and simulation models to explore the implications of intrametapopulation competition for metapopulation dynamics and for the fate of individual subpopulations. Results from these analyses indicate that relative 1) local population size (a function of habitat size or environmental quality) is a strong determinant of individual population persistence, 2) population persistence is a function of the relative strength of local versus global density-dependent mechanisms, 3) increased competition in common habitats increases the likelihood that marginal or at-risk populations will go extinct, 4) intrametapopulation competition increases the proportion of non-natal spawners in a depleted population, and 5) that competition may moderate (or exacerbate) the effects of positive (negative) spatial correlation on metapopulation persistence. These models provide a framework for estimating the effectiveness of management strategies and developing spatially-explicit guidelines for recovery of threatened wild salmonid stocks.

Keywords: metapopulation competition salmonid

This abstract is being presented at: 10:30 AM in session:
Oral Session #56: Metapopulation Analysis.