Body Size, Life History and the Structure of Host–Parasitoid Networks - Advances in Ecological Research - page 151

et al.,2010 ). This corroborates current theory, which suggests that when a high
cost to maximum fecundity is associated with dispersal between patches, then
the adherence of the population to the IFD, across its entire potential distribu-
tion, is reduced ( Bernstein et al.,1991 ). Conversely, if there is little fitness cost
associated with moving between patches, then host density at different patches
has less of an impact upon host encounter rates and there is no incentive to
allocate resources according to host density, resulting in density independent
parasitism and parasitoid aggregation ( Volkl, 1994; Wajnberg, 2006 ). In these
cases, foragers may still be optimising the number of hosts that they encounter,
and host abundance may still structure realised niche for these parasitoid
species, even though they do not conform to the IFD.
Similarly to stochasticity in host abundance, stochastic levels of juvenile
mortality have been suggested as an alternative mechanism by which para-
sitoids forage optimally. If offspring mortality is unpredictable, bet-hedging
strategies suggest that available host patches should be under-utilised in case
a stochastic event causes high offspring mortality ( Cronin, 2003 ). Similarly,
high levels of primary parasitoid offspring mortality due to hyperparasitism
have been reported, and it has been hypothesised that suboptimal patch use
may be a strategy of reducing offspring mortality resulting from the host
density-dependent aggregation of hyperparasitoids ( Mackauer and Volkl,
1993; van Veen et al., 2002 ). These studies suggest that some parasitoids
are unwilling to attack risky hosts, implying that host quality plays a role in
structuring a forager's realised niche.
C. Host Quality and Offspring Fitness
An alternative method of increasing individual fitness is to improve the
fitness of one's offspring ( Hubbard and Cook, 1978 ). Offspring fitness is
determined by host-choice decisions made by the parent; therefore, we would
expect that, in order to maximise fitness, parasitoids should preferentially
attack hosts that produce the fittest offspring while reducing the costs to
future reproduction associated with oviposition; that is, parasitoids should
utilise the most profitable hosts, as suggested in predator-prey food webs
( Dannon et al., 2010; Lacoume et al., 2006; Luo and Liu, 2011; Mackauer
et al., 1996; Morris and Fellowes, 2002; Nakamatsu et al., 2009; Ode et al.,
2005; Petchey et al., 2008; Sampaio et al., 2008 ).
In parasitoid and predator studies, body size is often used as a proxy for
fitness, because it is generally correlated with a greater potential fecundity
and a better ability to realise that potential ( Boivin, 2010; Kingsolver and
Huey, 2008; Lykouressis et al., 2009; Roitberg et al., 2001 ). Corroboratively,
body size has been suggested to be the primary constraint of potential
fecundity in insects from a range of orders of insects, suggesting a generally