Geoscience Reference
In-Depth Information
E. Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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F. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Appendix I. Supplementary Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Appendix II. Details on Regression Models. . . . . . . . . . . . . . . . . . . . . . . . . . .
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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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ABSTRACT
Here, we investigate patterns in the size structure of one marine and six fresh-
water foodwebs: that is, how the trophic structure of such ecological networks is
governed by the body size of its interacting entities. The data for these food webs
are interactions between individuals, including the taxonomic identity and body
mass of the prey and the predator. Using these detailed data, we describe how
patterns grouped into three sets of response variables: (i) trophic orderings; (ii)
diet variation; and (iii) predator variation, scales with the body mass of pre-
dators or prey, using both a species- and a size-class-based approach. We also
compare patterns of size structure derived from analysis of individual-based
data with those patterns that result when data are ''aggregated'' into species (or
size class-based) averages. This comparison shows that analysis basedon species
averaging can obscure interesting patterns in the size structure of ecological
communities. Specifically, we found that the slope of prey body mass as a
function of predator body mass was consistently underestimated and the slope
of predator-prey body mass ratio (PPMR) as a function of predator body mass
was overestimated, when species averages were used instead of the individual-
level data. In some cases, no relationship was found when species averages were
used, but when individual-level data were used instead, clear and significant
patterns were revealed. Further, when data were grouped into size classes, the
slope of the prey bodymass as a function of predator bodymass was smaller and
the slope of the PPMR relationship was greater compared to what was found
using species-aggregated data.We also discuss potential sampling effects arising
from size-class-based approaches, which are not always seen in taxonomical
approaches. These results have potentially important implications for parame-
terisation of models of ecological communities and hence for predictions
concerning the dynamics of ecological communities and their response to
different kinds of disturbances.
I. INTRODUCTION
When dealing with the apparently bewildering complexity encountered in
nature, ecologists have traditionally viewed multispecies systems (commu-
nities, food webs, ecosystems) through some kind of simplifying prism,
