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Jennings and Mackinson, 2003; Long et al., 2006; Maxwell and Jennings,
2006
). However, within a community, changes in predators' diet attributes
with body size could offset this reduction (
Arim et al., 2007, 2010
). It has been
shown that large predators can incorporate external energy inputs by con-
suming prey from other communities as a consequence of the predator's
(
McCann et al., 2005
) or prey's dispersal (
Pace et al., 2004
) and that those
species that occupy high trophic positions couple alternative energy paths or
sources of energy—for example, plants and detritus (
Miki et al., 2008;
Rooney et al., 2006
). Further, additional results suggest that prey diversity
could be important in allowing large predators to satisfy their energetic
demands. For example, fragmentation of tidal creeks led to a reduction in
fish prey diversity, which in turn was associated with a reduction in their
trophic position (
Layman et al., 2007
); reduction in lake diversity due to
human pollution may preclude the expansion of predator diet with size,
compromising the predators' energetic balance (
Sherwood et al., 2002
); and
diversity is positively associated with community biomass (
Long et al., 2006
)
and resource flow through the food web (
Krumins et al., 2006
). Because prey
richness and energetic demands increase with body size (
Cohen et al., 1993,
2003; McNab, 2002; Otto et al., 2007
), it is likely that the available biomass of
resources and energy flow towards large predators could also increase with
body size. In fact, this increase in prey richness with body size may be a
determinant of the stabilisation of population dynamics (
Otto et al., 2007
).
The eventual increase in the amount of available resources with body size
is directly connected with the concept of gape limitation (
Arim et al., 2010;
Hairston and Hairston, 1993; Layman et al., 2005
). Gape limitation refers to
all the constraints to the set of preys that can be consumed that are associated
to body size (
Arim et al., 2007; Brose et al., 2006a; Mittelbach, 1981
). These
include morphological restrictions to capture and process a prey item (
Pimm,
1982; Schmitt and Holbrook, 1984
) and could also involve systematic
changes in physiological abilities and constraints related to animal mass
(
McNab, 2002
). For example, larger animals can consume resources of
inferior quality, can travel far to find a patch of resources, and are less
constrained in resource use by the presence of predators than are smaller
predators (
Hopcraft et al., 2009; McNab, 2002; Sinclair et al., 2003
). All these
attributes associated with body size determine the existence of a systematic
increase in the range of preys that a predator can consume as its body size
increases (see also
Arim et al., 2010
).
A clear picture has emerged in food webs about the effect of body size and
gape limitation on trophic interactions (
Arim et al., 2010; Brose et al., 2006a;
Jacob et al., 2011; Woodward et al., 2005a,b
), via the existence of a hierarchy
in which large organisms consume small ones (
Brose et al., 2006a;
Cohen et al., 1993; Elton, 1927
). This applies, however, if considering only
free-living animals, rather than, for instance, host-parasite interactions
