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between parasitoids and their hosts are a reflection of the relative abilities of
different host populations to resist parasitoid attack, and not preferential
host-choice decisions made by the foraging parasitoids. To prove that the
distribution of link strengths within host-parasitoid networks is indeed due
to electivity on behalf of the forager, network analysis needs to be followed
up with behavioural studies of the foraging strategies exhibited by different
parasitoid species.
Foraging decisions made by parasitoids are dependent upon host charac-
teristics, including abundance and quality, which are temporally and spatial-
ly variable, and changes to these characteristics will have impacts upon
host-parasitoid network structure (
Bukovinszky et al., 2008; Laliberte and
Tylianakis, 2010; Tylianakis et al., 2007
). For example, in two different
studies, reductions in the quality (size) of phytophagous insect hosts, due to
changes in the host-plant community, resulted in the homogenisation of
host-parasitoid network structure (
Bukovinszky et al., 2008; Laliberte and
Tylianakis, 2010
). Similarly, as abiotic conditions, such as temperature or
weather patterns, affect the foraging efficiency of ectothermic invertebrates,
including searching and handling time in insect parasitoids, future climate
change could have a profound impact upon host-parasitoid network struc-
ture according to the frameworks presented in this review (
Bukovinszky
et al., 2008; Laliberte and Tylianakis, 2010; Tylianakis et al., 2007;
Woodward et al., 2010b
). The effect of temperature on foraging efficiency
could be exploited to investigate the effect of changing the costs and benefits
of host-choice decisions and whether any resulting changes in foraging
pattern corroborate the predictions made by the framework above.
Studies of sex ratio allocation decisions made by parasitoids in the pres-
ence of different host species have gone some way to investigating the
relationship between optimality and foraging strategy (
Chow and Heinz,
2005; Sequeira and Mackauer, 1992
). Due to the different impacts of male
and female parasitoids upon host populations, studies of the relationship
between host community structure and sex ratio allocation strategies could
provide some insight into the more complex, indirect relationships between
species within host-parasitoid networks, such as apparent competition
(
Heimpel et al., 2003; van Veen et al., 2006
).
The ideas and frameworks presented in this review have shed some light
upon the differences in the processes that structure host-parasitoid networks
and food webs. We conclude that while body-size considerations may play
a role in determining host-use patterns exhibited by some insect parasitoids,
the relationships between parasitoid life history and fundamental and
realised niche structures are the greater structuring force in host-parasitoid
networks. However, host-parasitoid networks and food webs are not
so profoundly different as to exclude collaborative studies that consider
interactions between the two network types within ecosystems.
