Indirect interaction between butterfly species mediated by a shared pupal parasitoid |
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Authors: | Saskya van Nouhuys Thomas S Kraft |
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Institution: | (1) Department of Biosciences, University of Helsinki, PO Box 65, Viikinkaari 1, 00014 Helsinki, Finland;(2) Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, New York 14853, USA |
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Abstract: | Indirect interactions among species can greatly affect their abundances and the structure of the community they live in. Using
a field experiment, we tested the hypothesis that congeneric butterfly species interact indirectly through a shared pupal
parasitoid. We predicted that symmetrical apparent competition would lead to high parasitism of both species, and the effect
would increase with regional butterfly abundance. Instead, parasitism of one host, Melitaea cinxia, was reduced in the presence of the second host, M. athalia. Parasitism of M. athalia did not differ whether or not M. cinxia was present. This pattern did not vary with regional butterfly abundance, though overall rate of parasitism did. Details
of the experiment suggest that the apparent commensalism occurred because M. cinxia pupae are protected by silk tents whereas M. athalia are exposed, causing locally foraging parasitoids to favour the more accessible host where the two are present together.
The local short-term apparent commensalism favouring M. cinxia opposes the landscape scale trend, in which parasitism increases where butterfly density is high. The outcome of this study
illustrates short-term apparent commensalism, that host suitability can depend on relative accessibility, and that indirect
interactions occurring at different scales may be in opposition. |
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Keywords: | Apparent competition Commensalism Community Foraging behaviour Melitaea cinxia Pteromalus apum |
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