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1 February 2003 Factors Initiating Emigration of Two Wolf Spider Species (Araneae: Lycosidae) in an Agroecosystem
Christopher M. Buddle, Ann L. Rypstra
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Coexistence of the wolf spiders (Araneae: Lycosidae) Hogna helluo (Walckenaer) and Pardosa milvina Hentz in soybean fields is partially driven by a trade-off in competitive ability and colonization success. H. helluo can out-compete P. milvina, but its population densities are limited by its colonization ability. However, even after repeated additions in soybean habitats, H. helluo seldom sustains high population densities. Our research focuses on whether emigration might explain this pattern. Relying on mark-recapture techniques, we tested the role of habitat quality and presence of heterospecifics as factors initiating emigration of H. helluo and P. milvina from suitable habitat patches. We assessed emigration by trapping spiders (with pitfall traps) at the outer edge of an unfavorable habitat (tilled soybean field) surrounding either no-till or mulched habitats (i.e., addition of straw), the latter representing an increase in habitat quality. Spiders were added to enclosures with con- or heterospecifics. Experiments were conducted twice, and ran for 4 d, at which time captures of marked spiders were low. Results showed H. helluo emigration was influenced by habitat quality because it was captured leaving no-till habitat significantly more often than exiting mulched habitats. In contrast, P. milvina activity was not driven by changes in habitat, and as such has more habitat versatility than H. helluo. The presence of con- or heterospecifics did not alter the propensity of either species to leave experimental units. H. helluo population densities are therefore limited by both its ability to colonize soybean fields and by its propensity to emigrate if suitable habitat is not available.

Christopher M. Buddle and Ann L. Rypstra "Factors Initiating Emigration of Two Wolf Spider Species (Araneae: Lycosidae) in an Agroecosystem," Environmental Entomology 32(1), 88-95, (1 February 2003).
Received: 28 January 2002; Accepted: 1 September 2002; Published: 1 February 2003

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