Document: CHR-3-81-1

A simple metapopulation model based on relationships between local demographic rates and regional density.

RAY, C.* ¹, M.PEACOCK ¹ and J.DUNHAM ²

University of Nevada Reno NV 89557 USA ¹
USFS Rocky Mountain Research Station Boise ID 83702 USA ²

Abstract:
Increasing fragmentation may endanger the remaining populations of a threatened cutthroat trout (Oncorhynchus clarki henshawi). Age-structured data available for several remaining interconnected stream populations show that survival within streams is a function of density summed across streams within this watershed. In some streams and age classes, local survival is negatively related to watershed-level density; in others, local survival is positively related to watershed-level density. These relationships suggest density-dependent movement of fish between streams. Relationships between local recruitment and the density of reproductives across the watershed also vary between streams. A simple metapopulation model is developed from these density-dependent relationships. This model requires no explicit dispersal data. By using the observed relationships between local demographic rates and metapopulation density, the model allows for implicit effects of both dispersal and habitat quality. Local dynamics are semi-independent, influenced by local response to regional stream flow which forces population fluctuation and fish redistribution. This modeling approach is superior to modeling local populations independently, which requires the often unrealistic assumption that local emigration and immigration will not vary with regional dynamics. The predictions of such 'local' models are compared with the predictions of this metapopulation model and with trout census data. Predictions from the metapopulation model are in better agreement with data. Results indicate the importance of metapopulation dynamics for persistence of this species.

Keywords: metapopulation modeling, age structure, density dependence, conservation, salmonids

This abstract is being presented at: 4:15 PM in session:
Oral Session #62: Freshwater Fish Ecology.