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SPATIAL AGGREGATION IN A FOREST FLOOR INSECT DEPENDS ON SEASONAL CONGREGATION AND SCATTERING EFFECTS OF PREDATORS
Citation:
Grear, J. SPATIAL AGGREGATION IN A FOREST FLOOR INSECT DEPENDS ON SEASONAL CONGREGATION AND SCATTERING EFFECTS OF PREDATORS. Presented at 89th Annual Meeting of the Ecological Society of America, Portland, OR, August 1-6, 2004.
Description:
Spatial aggregations arising from gregarious behavior are common in nature and have important implications for population dynamics, community stability, and conservation. However, the translation of aggregation behaviors into emergent properties of populations and communities depends on the mechanisms leading to aggregation. Non-social forms of aggregation such as those resulting from habitat preference, for example, are less likely to exhibit nonlinear trends in local abundance than those involving gregarious behavior. Despite the importance of distinguishing between social and landscape-driven aggregation, analytical techniques are not well-developed. Springtails (Collembola) are an ideal group for testing potential solutions to this problem because: 1) they are often cited as examples of social aggregation; 2) they live in spatially complex environments; and 3) the possibility that habitat structure, rather than gregarious behavior, causes springtail aggregation has not been tested outside of the lab. We combined the techniques of descriptive spatial sampling, individual-based observation, diffusion modeling and manipulative field experiments to test hypotheses explaining spatial aggregation in the collembolan Orchesella hexfasciata. Our results show that aggregation is a gregarious behavior triggered by seasonal increases in soil moisture. Experiments with the generalist lycosid spider Gladicosa gulosa also suggest that predators have a scattering rather than herding effect on litter-dwelling springtails. A different interpretation of driving mechanisms would have emerged from this study had we omitted one or more of the approaches we combined. More generally, our study tests several important modeling approaches for distinguishing between landscape-driven aggregation and the nonlinear effects of social attraction.