Shifts in activity and location are behavioral mechanisms of leaf-litter arthropods to tolerate variation in litter moisture. These mechanisms may become more important as precipitation trends become more varied with global climate change. Ten unfenced plots, 4-m2 in area, were established in a Kentucky forest. A clear roof constructed over 5 plots excluded rainfall to simulate drought conditions. From July 20 to September 23, 2001, water was sprayed on the 5 uncovered plots to simulate rainfall equal to 2X the long-term mean. Activity-densities of insects and arthropods were measured using pitfall traps designed to sample the top, middle, and bottom layers of leaf litter. Overall numbers of Collembola, insects that play a key role in litter decomposition, were significantly lower in drought plots than in plots receiving increased precipitation (300±40 vs. 660±60; p=0.0008). Surprisingly, overall spider numbers were significantly greater in the dry plots (17.4±1.9 vs. 11.6±1.5, p=0.046). Collembola numbers were lower in the top (p=0.0005) and middle (p=0.001) layers in dry compared to wet plots. Spider numbers were higher in the middle litter layers of dry compared to wet plots (p=0.01). Precipitation changes, even over a short time period, not only affected the behavior and location of two abundant groups of leaf-litter arthropods but also unexpectedly shifted predation pressure. Collembola, whose activity-density may have been negatively impacted by drought conditions, were also subjected to greater spider predation in the dry plots.
Keywords: Collembola, spiders
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