It is thought that in heterogeneous environments predator refuges and movement dynamics are key in determining which habitats act as sources of predators, and habitat manipulations for the purpose of achieving conservation biological control are based on this assumption. Salt marsh vegetation along the Atlantic coast of North America is characterized by a zonal distribution of plant species. High in the tide cycle grows Spartina patens, a grass with dense culms and a thick thatch layer. Another cordgrass, Spartina alterniflora, has sparser culms and less-developed thatch and occurs in two growth forms, a short form occupying a wide range of elevations, and a tall form occupying the lowest elevations, along the banks of tidal creeks. Previous anecdotes suggest that patens acts as an overwintering refuge for the wolf spider Pardosa littoralis, an important predator of planthoppers in both types of cordgrass. We tested this assumption by sampling spiders in both grass types early in the season following a severe winter and again following a mild winter. Results showed that following the severe winter, densities of overwintered adults were an order of magnitude higher in patens than in alterniflora and only their offspring (young spiderlings) emigrated from patens to alterniflora. Following the mild winter, densities of overwintered adults were equal in the two habitats. In both cases however, tall creekside alterniflora was occupied only by spiderlings. It appears that movement by spiders into alterniflora is affected by both winter severity and non-migration of overwintered adults into the lowest elevation habitats.
Species 1: Araneae Lycosidae Pardosa littoralis
Species 2: Homoptera Delphacidae Prokelisia
Keywords: overwintering habitat, source/sink dynamics
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