Document: MAR-3-51-20

Migration, nutrient transport, and dynamics in source-sink metapopulations.

HOLYOAK, M.* and M.J.DONAHUE

University of California, Davis CA 95616 USA ¹

Abstract:
Two branches of ecological theory address population dynamics in habitat patches that vary in the amounts of resources they contain. Source-sink theory predicts that births will exceed deaths for source populations with abundant resources, leading to a net production of emigrants, whilst sink populations typically have fewer resources and are net receivers of immigrants. By contrast a model of "balanced dispersal" predicts that patches will produce a net number of emigrants which is inversely related to the carrying capacity of the donor patch. We tested the appropriateness of these models for describing the long-term dynamics and net movement within replicated microcosms containing a food chain consisting of decaying seeds, bacteria and a ciliated protist, Colpidium striatum. Both the rates of decline of C. striatum populations and rates of decomposition of seed resources were strongly influenced by the amount of between-patch migration that was possible. Experimental estimates of the amount of between-patch movement of C. striatum broadly supported the balanced dispersal model. However, there were complex feedbacks between movement rate and within-patch dynamics that are not predicted by this model. Isolated patches were used to establish a relationship between protist body size and nutrient (seed) level. Estimates of protist body size within connected patches then provided evidence that migrating organisms moved nutrients with them. Net movements of individuals between patches did not predict either the amount or the direction of net fluxes of protist biomass, which were also influenced by the body size and density of migrating individuals. The results show the importance of studying who is migrating, when individuals differ, if we are to understand source-sink inversions and the subsidy of ecosystems by transport of materials and energy by migrating individuals.

Keywords: body size, decomposition, metapopulation, nutrients, population dynamics, Protista, source-sink, subsidy

This abstract is being presented at: 4:30 PM in session:
Oral Session #11: Trophic Cascades.