| 1. |
Insect host–parasite systems allow investigations
of the trophodynamics of ecological communities within a well-formed
theoretical context. A little explored feature of such systems
involves the interplay between generalized consumers and host–parasitoid
dynamics. I report a study investigating how the impacts of generalized
consumers, viewed here as interaction modifications, may influence
the stability of a particular interspecific interaction.
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| 2. |
In a study involving
overwintering oothecae of the praying mantis Stagmomantis limbata (Hahn),
birds damaged 36% of oothecae, 85% of which had also been parasitized
by winter-active, multivoltine torymid wasps of the genus Podagrion .
Birds preferentially preyed upon oothecae oviposited high on
trees, but such predation was often incomplete, leaving both
viable and parasitized mantid eggs inside damaged oothecae.
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| 3. |
Two factors allowed bird damage to influence
the distribution of risk of parasitism among oothecae and among
hosts. These were (1) that some parasites - but no
mantids - emerged successfully prior to bird predation and (2)
that extensive post-damage foraging by parasitoids occurred,
but that the nature of this foraging was altered little by oothecal
damage.
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| 4. |
In all, bird damage engendered a fourfold
increase (from 1·5 to 6·5) in the CV 2 of parasitism
risk among hosts (a stability criterion that has been proposed
for host–parasitoid interactions) and increased the relative
importance of host-density-dependent parasitism. The role of
timing of the two natural enemy impacts for stability of the
host–parasitoid interaction is discussed.
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