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The Effects of Spatial and Temporal Heterogeneity as Structuring Forces for Parasite Communities in Helisoma anceps and Physa gyrina

Kelli Kathleen Sapp and Gerald W. Esch
The American Midland Naturalist
Vol. 132, No. 1 (Jul., 1994), pp. 91-103
DOI: 10.2307/2426204
Stable URL: http://www.jstor.org/stable/2426204
Page Count: 13
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The Effects of Spatial and Temporal Heterogeneity as Structuring Forces for Parasite Communities in Helisoma anceps and Physa gyrina
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Abstract

A total of 1231 Physa gyrina and 1532 Helisoma anceps were collected over a 12-mo period from Charlie's Pond, in Stokes County, North Carolina. Similarity in the infra- and component parasite communities in Helisoma anceps and Physa gyrina provided an opportunity to compare the effects of various life history traits on infection by larval trematodes in a number of different microhabitats. In order to assess the effects of microhabitat partitioning on the infection status of the two snail species, collections were made twice per month. Site location, water depth, snail depth at capture, distance from shore, type of substratum, infection status, and host size were recorded for each snail. Multivariate statistics were used to assess which variables determined a snail's infection status. Data analysis indicated that certain of the microhabitat variables are better predictors of a snail's infection status than others. Comparing uninfected snails to those infected with a specific parasite species, there was much disparity with regard to which microhabitat characteristic varied significantly. Manipulation of infracommunity structure, by excluding certain parasites, allowed examination of the influence of temporal heterogeneity as compared to interspecific trematode interactions in structuring the infra- and component communities. Snails were maintained in cages in the field. Enclosures were positioned a few centimeters above the substratum to prevent infection of the snails via egg ingestion and effectively prevented the more prevalent parasite species (Halipegus occidualis in H. anceps and Halipegus eccentricus in P. gyrina) from infecting the snails. Statistical analyses indicate that preventing snails from ingesting eggs of some parasites had no affect on the recruitment of other parasites. Parasite prevalences in H. anceps and P. gyrina were not different in caged snails compared with those collected from the substrata of the pond.

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