Microhabitat distribution ofDrapetisca alteranda, a tree trunk specialist sheet web weaver (Araneae: Linyphiidae)

Abstract

We conducted systematic sampling to examine the microhabitat distribution of the Nearctic linyphiid Drapetisca alteranda Chamberlin 1909; adults are found almost exclusively on tree trunk surfaces. Sampling was conducted in a 1 ha plot in which all trees over 10 cm dbh had previously been identified, mapped, and measured. Tree trunks were sampled for D. alteranda by brushing spiders into beating sheets. We sampled equal trunk surface areas (0.5–2.0 m) of the four most abundant tree species on the plot: Quercus alba, Fraxinus pennsylvanica, Tilia americana, and Carya ovata. We measured tree bark furrowing depth at 15 locations around each tree. We analyzed the data with a General Linear Mixed Model, assuming Poisson distribution. Tree species and furrowing depth, but not tree size, were significant predictors of total number of D. alteranda collected. Eighty-four percent of the spiders were collected on T. americana, and the relationship between spider abundance and furrowing depth was negative. As a separate test for D. alteranda vertical distribution, we divided the lower 3 m of selected tree trunks into six 0.5 m sections, sampling each separately. Regardless of tree species, height above ground was a significant predictor of female (but not male) D. alteranda occurrence, with 52% of the females found 0.5–1.0 m above the forest floor. These results suggest that the microhabitat distribution of D. alteranda is broadly similar to that of the Eurasian species D. socialis, a species that matures in leaf litter and migrates mostly to the lower regions of tree boles to forage as adults.