Determinants of Density–Body Size Scaling Within Food Webs and Tools for Their Detection - Advances in Ecological Research - page 6

Gaston and Blackburn, 2000; Gaton and Lawton, 1988; Marquet et al.,1990 ).
Local analyses of population energy use have suggested that larger animals
could be capitalizing more energy than smaller ones ( Russo et al.,2003 ). The
analysis at the community level is identified as the LSDR ( White et al.,2007 ).
The three patterns of CCSR, GSDR, and LSDRare usually estimated applying
an OLS regression to log-transformed values of density and mean body size. In
the section focused on statistical issues, we examine the respective strengths and
weaknesses of this analysis in detail.
The ISD or size spectrum has been widely studied in aquatic ecosystems
( Sheldon and Parson, 1967 ). However, its consideration in terrestrial systems
indicates that this is also an important attribute of community structure in
other ecosystems ( Thibault et al., 2011 ). The idea behind this analysis is to
report the frequency of individuals in all the size classes ( Marquet et al.,
2005 ). In spite of being frequently called size spectrum, the term ''individual
size distribution'' better describes the nature of the pattern and therefore
should be preferred over the former ( White et al., 2007 ). The distribution of
body sizes can also be estimated at the species level, a pattern called SMSD,
which is related to LSDR and ISD (see Reuman et al., 2008 ).
III. DMR AND FOOD WEBS
The balance between forces that reduce density—competition and consump-
tion—and those that increase it—resource acquisition—across a wide range
of body sizes is a determinant of the DMR. The distribution of these interac-
tions among species is described by the structure of the food web, for example,
in so-called trivariate food webs that plot mean species body mass against
abundance on log-log scales (e.g. Cohen et al., 2003; Layer et al., 2010, 2011;
McLaughlin et al., 2010; O'Gorman and Emmerson, 2010; Woodward et al.,
2005a,b ). The analysis of DMRs in a food web context represented a signifi-
cant improvement in the understanding of both food web structure andDMR
( Cohen and Carpenter, 2005; Cohen et al., 2003; Jonsson et al., 2005 ).
A. Trophic Position
There is an abundance of compelling theoretical and empirical evidence that
demonstrates clear connections between species body size and trophic position
( Arim et al., 2007, 2010; Burness et al., 2001; Castle et al., 2011; Meli´n et al.,
2011; Nakazawa et al., 2011; Romanuk et al.,2010 ). It was recognized in some
of the earliest ecological work in this field that the efficiency at which energy is
transmitted in trophic interactions is typically low ( Lindeman, 1942 ), leading to
a reduction in species abundance in higher trophic levels ( Elton, 1927;