community metabolism would have required additional model complexity. This
could be included in future models that predict ecosystem process rates from
the size and abundance of organisms at multiple trophic levels.Closing remarks
This volume contains many valuable contributions towards the understanding of
the ecological consequences of body size that use a range of methodologies,
including observations of natural systems, experiments with natural systems,
theoretical modelling and experiments with artificial ecosystems. We present
examples of the last approach, using new analyses of data from our published
experiments. These analyses have demonstrated effects of body size at three levels
of organisation, and how these effects can be altered by community properties
such as trophic complexity and species richness. We have illustrated the utility of
experimental microbial systems for evaluating allometric theories of community
structure and metabolism, and shown that patterns based on observations across
many natural systems readily emerge in experimental systems where attributes
such as organism sizeand trophic complexity are subject to rigorousexperimental
control. These results also point to an important role for biodiversity in influenc-
ing community biomass and metabolism that remains incompletely integrated
into allometric theories of community and ecosystem properties. Discrepancies
between the predictions of allometric theory and our findings could be due to any
of many properties of real organisms, for example, evolution can produce a
mass–density relationship (Loeuille & Loreau,2006 ). Integration of biodiversity,
trophic structure and evolution remains an important challenge for ecologists
working at the interface of population, community and ecosystem ecology.Acknowledgements
Jill McGrady-Steed kindly made the data from her experiment available in
electronic format. Those data and others were originally collected with the
support of the US NSF under grant 9806427 to PJM and Timothy Casey.
Discussion with participants of the British Ecological Society Special
Symposium on Body Size and the Organisation and Function of Aquatic
Ecosystems, and the comments of two anonymous reviewers improved the
content of this manuscript. OLP is a Royal Society University Research Fellow.References
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