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than smaller ones (
Jetz et al., 2004
). Scale of movement can cover many
orders of magnitude, according to the abiotic environment, and increases in a
non-linear fashion with individual body size (
Rooney et al., 2008
). This is
because the energetic cost of movement for any given distance is reduced in
larger organisms (
Brown et al., 2004; Woodward et al., 2005
). The allometric
scaling of range size suggests that larger individuals forage in a more hetero-
geneous environment and are more likely to interact with a wider range of
species than smaller predators (
Rooney et al., 2008
). In terms of network
structure, this means larger predators potentially have a broader fundamen-
tal niche (
Gilljam et al., 2011
) and, due to the reduced cost of moving
between resource items, are more likely to exhibit preferential prey selection,
akin to the parasitoid in
Figure 4
B(
Rooney et al., 2008
).
An important aspect of the size structuring of food webs is the relation-
ship between body size and trophic level (
Gilljam et al., 2011; Yvon-
Durocher et al., 2011
). In many food webs, energy flows from many
small organisms to fewer large ones (
Brose et al., 2006
). Studies have
suggested that the ordering of trophic links in this way can be attributed
to how foraging traits covary with body size, whereby larger individuals
have more potential pathways of energy available from which they can
sustain their greater individual biomass (
Arim et al., 2010; Brose et al.,
2006; Petchey et al., 2008; Woodward et al., 2005
). This is because, in
predator-prey interactions, many so-called 'forbidden interactions' are
related to the mismatching of body size as a trait-pairing characteristic
(
Oleson et al., 2010
). Conversely, the strength of body size as a constraint
upon potential feeding interactions is a continuous variable dependent
upon the type of interaction. For example, benthic suspension feeders
often do not have diet breadths constrained by the size of the consumer;
as a result, in these interactions, resource size does not scale with consumer
size (
Riede et al., 2011; Yvon-Durocher et al., 2011
). Arguments based on
'gape limitation' have described the manner in which body size is related to
trophic status in fish, as the diet of a fish is severely limited by the shape of
its feeding apparatus; however, this limitation is reduced in larger indivi-
duals compared with smaller ones (
Arim et al., 2010
). As a result of this
relaxation with increased body size, larger predators are able to feed on a
broader range of species from a wider range of habitats, simultaneously
increasing the number of available energy pathways and the individual's
'trophic level' (
Arim et al., 2010; Brose et al., 2006; Woodward et al., 2005
).
Petchey et al. (2008) and Woodward et al. (2010a)
, which utilised individu-
al-based data and found an even stronger fit, successfully predicted the
organisation of trophic interactions in a range of food webs utilising
hypothesised allometric scaling of predator handling time and prey nutri-
tional content, and optimal foraging theory. In the model, termed the
allometric diet breadth model (ADBM), the size of the largest prey that
