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mechanisms (
Cohen et al., 2003; Jennings and Mackinson, 2003; Jonsson
et al., 2005; Loeuille and Loreau, 2006; Maxwell and Jennings, 2006
) and is
recognized as a main attribute of community organisation (
Brown, 1995
).
It has long been observed that the DMR presents significant variation
among studies (
Blackburn and Gaston, 1997; Gaston and Blackburn, 2000
).
This variation has been related to the analysed communities (
Silva and
Downing, 1995
), ecosystems (
Cyr et al., 1997a,b
), taxonomic groups
(
Cotgreave and Harvey, 1992; Silva et al., 1997
), spatial scale of analysis
(
Russo et al., 2003
), trophic levels (
Marquet et al., 2005
), and the strength of
variation in trophic position with body size (
Brown and Gillooly, 2003;
Cohen et al., 2003; Jennings and Mackinson, 2003
). In addition, it has also
been reported that the DMR within a single ecosystem could be robust to
temporal or spatial changes in species diversity, number of individuals, and
human-derived pressures (
Marquet, 2000; Marquet et al., 1990
). Compared
with the large attention devoted to the report of empirical patterns, work
considering the mechanisms accounting for changes in the DMR is still
surprisingly scarce (
Jennings et al., 2007; Maxwell and Jennings, 2006
).
Animals satisfy their energetic demands by making use of the energy flow
through food webs, and this has been recently shown to be connected to the
expected DMR (e.g.
Brown and Gillooly, 2003; Carbone and Gittleman,
2002; Loeuille and Loreau, 2006; Long et al., 2006; Maxwell and Jennings,
2006; Reuman and Cohen, 2004; Reuman et al., 2008
). The patterns of
individual's and species' insertion within food webs, determined by the
trophic position, prey, and predators richness and the predator-prey mass
ratio, are closely related to body size (
Arim et al., 2007, 2010; Carbone and
Gittleman, 2002; Carbone et al., 1999, 2007; Olesen et al., 2010; Otto et al.,
2007; Pettorelli et al., 2009; Riede et al., 2011
). The explicit connection
between the position of species of different sizes within food webs and the
related DMR has been a recent focus of attention in community ecology (e.g.
Brown and Gillooly, 2003; Loeuille and Loreau, 2006; Long et al., 2006;
Maxwell and Jennings, 2006; Reuman and Cohen, 2004; Reuman et al., 2008,
2009
). A consistent regularity in food webs, related to community stability, is
the recurrence of hierarchies in trophic interactions, whereby large free-
ranging animals consume small ones (
Brose et al., 2006a,b
). This ''gape
limitation'' constrains the set of resources to which individuals have accesses,
leading to an increase in the available resources as consumers become larger
(
Arim et al., 2010; Gilljam et al., 2011; Woodward et al., 2010
). In addition,
predation and its effect on density are not homogeneous across size classes
(e.g.
Brooks and Dodson, 1965; Sinclair et al., 2003
). In this chapter, we draw
attention, both theoretically and empirically, to the effect of these changes in
trophic interactions related to body size, on the DMR.
The analysis of the relationship between mass and abundance has proved
to be a much more difficult task than a simple regression on log-transformed
