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Alternatively, if handling time is more costly than searching time, then fitness
costs are associated with attacking a host, and parasitoids should only use
hosts that satisfy a minimum quality threshold. Life-history traits determine
the number of eggs a parasitoid has to allocate, the time it has to do it in and
often provide constraints upon host and space use; therefore, the likelihood of
different species being egg or time limited is strongly related to parasitoid life
history (
Rosenheim et al.,2008
). Through this mechanism, life-history char-
acteristics will change the propensity of foragers to exhibit different foraging
strategies and, therefore, can be used to predict host-choice decisions made by
different species (
Figure 13
).
Realised networks are constructed from the foraging decisions made by all
the individuals within a species population; therefore, optimal foraging
strategies play an important role in the formulation of the structure of
ecological networks (
Petchey et al., 2008
). In host-parasitoid networks, the
interactions strengths between the parasitoid and the available host species
can either be determined by host characteristics, such as quality, if the
parasitoid exhibits a high degree of electivity (expected in handling-time- or
egg-limited individuals), or by the relative abundances of each host species, in
searching time limited individuals (
Figure 13
;
Minkenberg et al., 1992
).
C. Future Research Avenues and the Effect of
Spatio-Temporal Variation in Host-Parasitoid Networks
Analysis of host-choice decisions from quantitative host-parasitoid net-
works in relation to parasitoid life history will help elucidate a mechanistic
understanding of the structuring of these networks. For example, the degree
of electivity exhibited by different parasitoid species could be investigated in
regards to their morphology and ecology. Similarly, behavioural studies
investigating the relationship between life history and foraging strategy by
looking at the state-dependent behaviour of individual foragers, in terms of
their host-choice decisions, could further clarify the relationship between life
history and the currency of optimisation. Linking together state-dependent
foraging patterns and network structure in parasitoids would contribute to
the strong shift towards individual-based foraging models (
Abrams, 2010
).
The idea of state-dependent foraging contributes a new facet to the ideas
presented in this review, namely, that the factors that determine host-
parasitoid interactions are not constant through space or time (
Duffy and
Forde, 2009; Oleson et al., 2010
). For example, the susceptibility of hosts to
their parasitoids changes through time; strong exploitation interactions by a
parasitoid wasp, A. colemani, resulted in the evolution of a strain of peach-
potato aphid, Myzus persicae, that was highly resistant to attack (
Herzog
et al.,2007
). It is possible, therefore, that differences in interaction strengths
