On Valuing Patches: Estimating Relative Contributions to Metapopulation Growth
Friday seminar by James D. Nichols
Forty years ago, Richard Levins (1969, 1970) introduced the concept of the metapopulation, formalizing the relevance of dispersal among local populations, both to those local populations and to the entire system. Ron Pulliam (1988) later considered the relative values of interacting local populations with his definitions of sources and sinks. Here, I follow the framework developed by Runge et al. (2006) and define contribution metrics reflecting the relative and absolute importance of each specific local population to population growth of (1) every other local population and (2) the entire system. I then describe reverse-time multistate capture-recapture models as a natural framework for drawing inferences about these contributions. Finally, I apply these models to a system of 8 local populations of the banner-tailed kangaroo rat (Dipodomys spectabilis) studied by Peter Waser in Arizona. The analysis yields contribution matrices for the entire system, with elements expressing the contributions of young and adults from each local population to adult population change in every other local subpopulation. The modeling permitted inferences about potential sources of variation in these contributions: (1) age, (2) general location of the local population in the system (central vs. peripheral), and (3) relative metapopulation size (years of high density and low density). I also present estimates of the relative contributions of each local population, and of extra-system immigration, to the entire metapopulation system.
James D. Nichols, U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel MD, USA