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mediated apparent competition, and determine whether these processes
significantly shape host-parasitoid networks (
Tack et al., 2011
). In theory,
this size-selective sex allocation could result in a size structured indirect
interactions within networks where negative apparent competition effects
are typically directed from larger hosts to smaller hosts.
VIII. CONCLUSIONS
This review has discussed the empirical evidence for a mechanistic relation-
ship between parasitoid life-history traits and the structure of host-
parasitoid networks. To conclude, we combine the series of ideas that have
been presented thus far and construct an organised framework, based on
optimal foraging theory, that will illustrate which aspects of parasitoid life
history are important in determining host-parasitoid network structure and
how these aspects interact with each other. This framework will be compared
with the body size based framework suggested by the ADBM, which has been
used so successfully to provide a mechanistic understanding of the structure
of food webs (
Petchey et al., 2008; Woodward et al., 2010a
).
The structure of ecological networks has been defined as the differences
between each species' fundamental and realised niches, as well as consider-
ing how the relative interaction strengths between species pairs vary within
the realised niche. Therefore, for ease of understanding, the frameworks
presented here have been split into two groups: those that consider the
structure of fundamental niche, which includes the determination of both
diet breadth and trophic level, and those that consider the realised niche
structure, which focuses upon what influences optimal foraging decisions
made by consumers.
A. The Determinants of Fundamental Niche
Predator body-size relationships have been hypothesised, and shown, to play
an important role in determining fundamental niche structure (
Arim et al.,
2010; Brose et al., 2006; Petchey et al., 2008; Riede et al., 2011; Yvon-
Durocher et al., 2011
) (summarised in
Figure 11
). The allometric scaling
relationships for consumer handling capabilities, such as 'gape limitation'
constraints, according to the ADBM (
Brose et al., 2006; Petchey et al., 2008
),
and space use parameters, such as the scale of movement, according to
Rooney et al. (2008) and
Woodward et al. (2005)
, are strong determinants
of diet breadth in marine and terrestrial food webs. These relationships occur
in such a way that, in many food-webs, diet-breadth broadens with consumer
size (
Arim et al., 2010; Brose et al., 2006
). Studies have also observed a
