PARENT SESSION
Poster Session #6: Invasive Species Ecology: Insects and wetlands.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Consequences of an Allee effect on the invasion of Spartina alterniflora in Willapa Bay, WA.

TAYLOR, CAZ^*,1,2, DAVIS, HEATHER^2,3, CIVILLE, JANIE³, ¹ Department of Environmental Science and Policy, Davis, CA² Center for Population Biology, Davis, CA³ Section of Evolution and Ecology, Davis, CA

ABSTRACT- A spatially-explicit model of the spread of Spartina alterniflora (smooth cordgrass) in Willapa Bay, WA was constructed. Parameter values were estimated from field measurements and from GIS maps. Previous field work has shown that this population experiences reduced seed production at low densities demonstrating the presence of an Allee effect. The model was used to explore the consequences of the Allee effect, variation in seed dispersal, recruitment and self-fertilization rates on the dynamics of the invasion. For each simulation run the Allee effect was either present or absent and other non-dimensional parameters were varied randomly within ranges of ±10%. Response variables include area occupied after 50 years, average speed of invasion, length of establishment phase and spatial autocorrelation statistics designed to summarize aspects of the spatial pattern. The General Linear Model (GLM) was used to analyze the importance of the Allee effect, other parameters and interaction effects on each response variable. The Allee effect was responsible for a longer establishment time, slower overall invasion and less total area occupied after 50 years. The effects of other parameters and interactions are discussed.

KEY WORDS: Spartina alterniflora, Invasive species, Allee effect, Spatially-explicit model