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Spatial dynamics of mutualistic interactions.
Amarasekare, Priyanga*,1, 1 University of Chicago, Chicago, IL, 60637
ABSTRACT- I present a model of mutualistic interactions in a patchy landscape. The interaction can be that between a plant and pollinator, or more generally, between two mutualists that differ in mobility. The landscape consists of two sites, each containing a collection of empty, plant-only, and plant-pollinator patches. Within-site dynamics involve extinctions and colonizations of plant and pollinator. Between-site dynamics involve pollinator emigration and immigration. Within a given site, an Allee effect can occur such that both plant and pollinator go extinct if the fraction of plant-pollinator patches falls below a critical threshold. Pollinator dispersal can rescue such sink communities from extinction, provided there is a source community with plant-pollinator patches above the extinction threshold. Thus, source-sink dynamics allow for the persistence of a mutualistic interaction that could otherwise go extinct. Persistence however, depends on the source-sink structure. If pollinators from one site can colonize plant-only patches at the other site, the spatial structure is equivalent to a mainland-island situation where dispersal does not affect local dynamics of the source community. Persistence of sink communities is guaranteed as long as pollinator colonization rate exceeds a threshold. In contrast, if propagules are produced locally but a fraction migrates between sites, dispersal affects the local dynamics of both source and sink communities. Now there are both upper and lower limits to migration. Persistence requires that migration exceed a lower threshold. However, too high a migration rate can cause a net loss of pollinators from the source community, resulting in landscape-wide extinction of the mutualistic interaction.
KEY WORDS: mutualistic interactions, source-sink dynamics, migration, spatial structure