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| We employ size-based theoretical arguments to
derive simple analytic predictions of ecological patterns
and properties of natural communities: size-spectrum exponent,
maximum trophic level, and susceptibility to invasive
species. The predictions are brought about by assuming that
an infinite number of species are continuously distributed
on a size–trait axis. It is, however, an open question whether
such predictions are valid for a food web with a finite number
of species embedded in a network structure. We address
this question by comparing the size-based predictions to
results from dynamic food web simulations with varying
species richness. To this end, we develop a new size- and
trait-based food web model that can be simplified into an
analytically solvable size-based model.We confirm existing
solutions for the size distribution and derive novel predictions
for maximum trophic level and invasion resistance.
Our results show that the predicted size-spectrum exponent
is borne out in the simulated food webs even with few
species, albeit with a systematic bias. The predicted maximum
trophic level turns out to be an upper limit since
simulated food webs may have a lower number of trophic
levels, especially for low species richness, due to structural
constraints. The size-based model possesses an evolutionary
stable state and is therefore un-invadable. In contrast, the
food web simulations show that all communities, irrespective
of number of species, are equally open to invasions.We
use these results to discuss the validity of size-based predictions
in the light of the structural constraints imposed by
food webs. | |
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