Parasitoid-mediated effects: apparent competition and the persistence of host–parasitoid assemblages |
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Authors: | M B Bonsall and Michael P Hassell |
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Institution: | (1) Department of Biology and NERC Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berkshire, SL5 7PY, UK Tel. +44-1344-623-911; Fax +44-1344-294-339 e-mail: m.bonsall@ic.ac.uk, GB |
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Abstract: | Indirect effects such as apparent competition (in which two hosts that do not compete for resources interact via a shared
natural enemy) are increasingly being shown to be prevalent in the structure and function of ecological assemblages. Here,
we review the empirical and theoretical evidence for these enemy-mediated effects in host–parasitoid assemblages. We first
address questions about the design of experiments to test for apparent competition. Second, we consider factors likely to
affect the coexistence of host species that share a parasitoid and are involved in apparent competition. We show that parasitoid
aggregation, and the switching effect that this can generate when hosts occur in separate patches, not only promotes persistence
but is also strongly stabilizing. The broader consequences of these effects are discussed.
Received: November 6, 1998 / Accepted: January 13, 1999 |
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Keywords: | Aggregation Coexistence Heterogeneity of risk Indirect interactions Switching |
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