Geoscience Reference
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community, and this should therefore enable us to develop a classification
scheme for the functional roles of consumers.
Recent research has shown that species from higher trophic levels (
Pauly
et al., 1998
), large-bodied or slow-growing species, with late maturity tend to
decline or go extinct more rapidly than those that are smaller (
Cardillo, 2003;
Layer et al., 2011; McKinney, 1997
). This suggests that some life-history
traits like body size are linked to susceptibility to extinction and thus may be
more likely to trigger secondary extinctions. Body size is a useful 'super-trait'
for collapsing many functional attributes of a given species into a single,
relatively easy to measure dimension. Along with temperature, it largely
determines an individual's basal metabolic rate and its growth rate, which
in turn are associated with natural mortality rates, longevity, age at maturity
and reproductive output (
Brose et al., 2005a,b; Castle et al., 2011; Ings et al.,
2009; Peters, 1983; Woodward et al., 2010a; Yvon-Durocher et al., 2011
).
A recent study (
Riede et al., 2011
) has shown that predator body mass
increases with trophic level across a variety of predator types and across
ecosystems (marine, stream, lake and terrestrial). These results supported
theoretical predictions that predators are, on an average, larger then their
prey and that they are, on average, more similar in size to their prey at higher
trophic levels than at the base of the food web (
Jonsson et al., 2005; Layman
et al., 2005; Romanuk et al., 2011
). There are some apparent exceptions,
including interactions between herbivore and plants, parasite-host relation-
ships and benthic stream invertebrates as well as some marine benthic
invertebrates, for which a different kind of size-structure seems to apply,
that is, different feeding strategies enable most benthic invertebrates to feed
on prey items larger then themselves (
Riede et al., 2011
).
Most food web studies are from relatively species-poor networks (i.e. low
species/node numbers), and thus fairly simply structured networks, such
as Tuesday Lake (
Cohen et al., 2003; Jonsson et al., 2005
), and/or from
communities that to some extent have been disturbed, such as the acidic
Broadstone stream (
Woodward et al., 2005
). Few studies are from species-
rich, highly complex communities, and for this reason, our knowledge about
what characterises such systems is poor. Further, for large, species-rich food
webs, a food web graph and traditional food web statistics can do little more
than conveying a fraction of the immense complexity of these entangled webs
(e.g.
Woodward et al., 2008
), and new complementary ways of describing
food web structure that are linked to functional attributes are needed.
We aimed to address this gap in our current knowledge by characterising the
species-rich and pristine Weddell Sea food web and developing a new classifi-
cation scheme for the functional roles of consumers to describe and analyse the
trophic complexity of this system. The Weddell Sea food web data represent a
unique opportunity to analyse an exceptionally large and relatively undisturbed
complex community from a large and globally important three-dimensional
