PARENT SESSION
Oral Session #32: Animal Community Ecology. Presiding: M. Weiss.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Hall of Ideas P&Q.

The effect of precipitation change on leaf litter spider communities.

Cramer, Kenneth¹, ¹

ABSTRACT- At Oak Ridge National Labs in Tennessee, a long-term manipulative experiment was initiated in 1993 to study the potential impacts of precipitation change due to global warming on a temperate deciduous forest. The Throughfall Displacement Experiment (TDE) diverts 33% of ambient rainfall from one 80 by 80m plot to another. Because spiders are important predators of the epigean fauna that have shown the potential to affect nutrient cycling via trophic cascades, I evaluated the impacts of the TDE on spider abundance, diversity, and species composition. Samples of leaf litter from 0.2m² circular plots in the wet, ambient (control), and dry plots were hand sorted for spiders. Leaf mass (as an estimate of leaf volume and habitat area) had a significant positive correlation with spider abundance, more so of selected taxa, especially Dictyna. Total spider abundance was unchanged across treatments, although leaf mass was significantly greater in the dry plots. Changes in species richness were probably minimal, yet difficult to assess using extrapolation techniques because collection curves had not reached an asymptote in some cases. Species composition, however, was dramatically affected by the treatments, and certain species showed rather strong habitat associations correlating with treatment or position on the slope of the experimental plots.

KEY WORDS: spiders, precipitation, communities, richness