Geoscience Reference
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3.
Handling
constraints
Maximum prey
size
1.
5.
3.
Predator body
size
Trophic level
2.
Scale of
movement
6.
Diet breadth
4.
Figure 11 Effect of predator body size on fundamental niche structure. (1) Larger
predators are less physiologically constrained in the size diversity of hosts that they
are capable of handling, for example, gape limitation in fishes ( Arim et al., 2010;
Brose et al., 2006; Petchey et al., 2008 ). (2) Larger predators forage across a greater
scale of movement, which encompasses a more diverse array of habitats than is the
case for smaller predators ( Jetz et al., 2004; Rooney et al., 2008; Woodward et al.,
2005 ). (3) The size of the largest resource that can be handled successfully scales
with predator-size faster than the smallest, resulting in a broader diet breadth ( Brose
et al., 2006; Petchey et al., 2008; Woodward and Hildrew, 2002a,b ); however,
this relationship is not present across all interaction types, and this model is not
suitable for the description of benthic suspension feeders ( Riede et al., 2011 ) or host-
parasitoid networks ( Petchey et al., 2008 ). (4) Because they forage across a more
heterogeneous environment, larger predators encounter, and thus are capable of
interacting with, a wider range of prey species ( Gilljam et al., 2011; Rooney et al.,
2008; Woodward et al., 2005 ). (5) Because of the allometric scaling of trophic level,
larger predators, which eat larger prey and are themselves only consumed by higher
trophic levels, must be higher in the food web ( Gilljam et al., 2011; Riede et al., 2011 ).
(6) A broader diet implies that larger predators consume resources from a greater
number of energy pathways than smaller predators; therefore, the inherent scaling of
diet breadth with body-size results in a positive relationship between body size and
trophic level ( Arim et al., 2010; Brose et al., 2006; Gilljam et al., 2011; Petchey et al.,
2008; Woodward and Hildrew, 2002a,b ).
positive relationship between consumer body size and trophic level ( Riede
et al., 2011 ); this has been suggested to be because a broader diet results in a
greater number of energy pathways by which an individual can sustain its
biomass, which simultaneously results in the individual inhabiting a higher
trophic level ( Arim et al., 2010 ). Similarly, larger predators consume larger
prey, which further reinforces the size structuring of fundamental niche in
food webs ( Petchey et al., 2008; Riede et al., 2011 ).
Despite these recurrent patterns across many systems, there is variability
in the strength by which ecological networks are structured by body size
( Yvon-Durocher et al., 2011 ). This strength can be considered as the degree
to which size constraints determine forbidden interactions in a network
( Oleson et al., 2010; Vazquez et al., 2009; Yvon-Durocher et al., 2011 ). For
example, in benthic suspension feeders, where resource consumption barriers
are typically not determined by consumer body-size characteristics, there is
 
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