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or link-averaged PPMR), on which the species-based model is based, are
variable among food webs (
Table 2
).
The second modelling approach requires the modification of size-based
community-spectrum models to differentiate species. This approach has the
advantage that individual-based PPMR (individual-predator or individual-
link PPMR), which is the key parameter in this type of modelling, is usually
directly related to species identity and body mass in most food webs
(
Table 2
). In the original size-based spectrum model, it was assumed that
primary production by small organisms is transferred directly to higher
trophic levels with a constant PPMR. A way to utilise the size-based spec-
trum model through incorporating interspecific PPMR variation is to inves-
tigate the ecological consequence of coupling different trophic paths.
Aquatic ecosystems provide a good example of such research, where pelagic
food webs (i.e. phytoplankton-zooplankton-planktivores-piscivores) are
usually linked to benthic food webs supported by detritus and/or periphyton
(
Rooney et al., 2006
), which is known as pelagic-benthic coupling (
Schindler
and Scheuerell, 2002; Vadeboncoeur et al., 2002
).
Blanchard et al. (2009,
2011)
presented coupling models of phytoplankton-based and detritus-based
trophic pathways, which capture the PPMR-related differences between the
two paths, whereby the benthic food web had less clear size-dependent
feeding than the pelagic food web. Given that PPMR is expected to be larger
in aquatic systems than in terrestrial systems, especially for ectothermic
vertebrates (
Brose et al., 2006a
), a similar application would be possible for
aquatic-terrestrial food webs coupled through resource subsidy (
Doi, 2009;
Polis et al., 1997, 2004
) and the ontogenetic niche shift of animals, such as
aquatic insects and amphibians (
Nakano and Murakami, 2001; Nakazawa,
2011a,b
). Given the generality and diversity of coupled food webs in nature
(
Bardgett and Wardle, 2010; Schindler and Scheuerell, 2002; Vadeboncoeur
et al., 2002
), an interesting question is how individual-level PPMR differs
among distinct types of ecosystems, or how the coupling of food webs with
different PPMRs mediates the structure and dynamics of the whole system.
Another way to modify the size-based spectrum model is to split the
community-size spectrum into species.
Andersen and Beyer (2006) and
Hartvig et al. (2011)
assumed that asymptotic body size and size at maturity
are species specific. The model by
Hartvig et al. (2011)
is especially notable in
that different species were given different feeding efficiencies, even at the
same body mass. The researchers weighted the experienced community size
spectrum for each species, explaining that it would represent interspecific
interaction strength, and hence species-based food-web architecture. How-
ever, their model still employs the conventional assumption that all species
maximise foraging efficiency at the same PPMR, despite absolute levels being
different.
