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Community Structure and Environmental Stress: Desiccation Promotes Nestedness in Mycophagous Fly Communities
Wade B. Worthen, M. Tildon Jones and Robert M. Jetton
Vol. 81, No. 1 (Feb., 1998), pp. 45-54
Stable URL: http://www.jstor.org/stable/3546466
Page Count: 10
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In a previous field experiment, communities of mycophagous flies that emerged from Agaricus bisporus mushrooms exhibited a nested-subset pattern related to mushroom size. A phorid species and Leucophenga varia (Drosophilidae) emerged from small, medium, and large mushrooms, but other drosophilid species were usually limited to large mushrooms. Here, we conducted two experiments and one field survey to determine whether this nestedness pattern is caused by nested desiccation tolerances among species, coupled with the mediating effects of mushroom size. In the first experiment, 20 first instar larvae of either Drosophila tripunctata or D. putrida were added to A. bisporus mushrooms that weighed 5 g, 10 g, or 20 g. Mushrooms were placed in environmental chambers at different temperatures for 5 d (maxima of 25°C, 30°C, or 35°C). Both mushroom size and temperature had significant direct effects on the proportion of larvae completing development; larvae in small mushrooms are more susceptible to desiccation stress than larvae in large mushrooms. In a second experiment, we examined the effect of desiccation stress on community structure. Woodland mushrooms collected in the field were cut in half; the halves were placed at different incubation temperatures (maxima of either 25°C or 35°C) for 5 d, and emerging flies were counted and sorted by species. The halves incubated at 35°C produced significantly nested communities, the halves incubated at 25°C did not. Correlations between fly abundance and mushroom mass were also more significant at higher temperatures. These results were consistent with the hypothesis that desiccation stress, differentially mediated by mushroom size, drives nested subset structure in these communities. In a four-week field survey, however, nestedness was not related to mean temperature or rainfall. We contend that small habitats are less resistant to changes in environmental conditions than larger habitats, so the intensity of environmental stress will correlate with habitat size. So, some initially variable and non-nested communities might decay to a nested-subset pattern of species composition as a result of differential habitat buffering under stressful environmental conditions.
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