Sunday, December 10, 2006 - 9:47 AM

Winter severity affects the use of refuge habitats by predators: Implications for spatial variation in the top-down control of herbivore populations

Danny Lewis, and Robert F. Denno, University of Maryland, Entomology, 4112 Plant Sciences Building, College Park, MD

The location of refuge habitats for predators and their reliance on them can have profound spatial effects on prey populations as predators move into neighboring habitats with the onset of spring. Along the Atlantic coast of North America stands of the salt marsh cordgrass Spartina patens serve as the winter refuge for the wolf spider Pardosa littoralis, an abundant predator that colonizes neighboring stands of Spartina alterniflora annually. The refuge effect results from a well-developed thatch layer present only in S. patens. We present six years of data showing that Pardosa density during winter and spring is consistently higher in S. patens than in adjacent S. alterniflora. Although spider densities declined in both habitats following cold winters, the decline was more pronounced in S. alterniflora than in S. patens, suggesting that S. patens provides better winter refuge. Notably, the winter residence of Pardosa in S. patens habitats cannot be attributed to greater prey availability there. The extent to which Pardosa relies on S. patens for winter refuge influences its spring distribution in S. alterniflora, the spatial extent of this predator subsidy, and ultimately the strength of top-down control on herbivore populations. Thus, severe winters impose spatial constraints on predator distribution with potential landscape level consequences for herbivores.

Species 1: Araneae Lycosidae Pardosa littoralis
Species 2: Hemiptera Delphacidae Prokelisia marginata