meiofaunal species would predate on or compete with them (many meiofaunal
predators take relatively large prey, often larger than themselves). According to
Warwick, this general regional pattern of species–body size then produces the
local patterns observed. In contrast,Schmid and Schmid-Araya(this volume)
analyze such community patterns in relation to fractal geometry, potentially
the most fundamental of all the approaches in this volume since fractals may
underly the scaling of metabolic rate with body size itself. Schmid and Schmid-
Araya did not find a self-similar pattern of body size across all scales, however,
referring to the changes in scale as ‘multifractal’. Interestingly,Warwick(this
volume) also rejected a single fractal scaling for the marine benthos.
Other chapters took experimental or modelling approaches. In their experi-
ments using model ecosystems of protists,Petchey, Long and Morin(this vol-
ume) demonstrated the effects of body size at three levels of organization: the
population, community and ecosystem. The results were encouraging, but there
were discrepancies with allometric theory and we can conclude that the effects
of body size on ecological processes are modified by trophic complexity (con-
nectedness) and species richness.Persson and De Roos(this volume) also looked
at model systems, but focused on individual variation using physiologically
structured population models. They stress the within-species variation, much
of it ontogenetic, in food intake, growth and body size that is so characteristic of
most metazoans. This variation generates intrinsic dynamics and divergent
body-size distributions, not wholly predictable by metabolic theory for instance.
Systems with strong cohorts that are constantly changing are non-equilibrial
systems that can approach alternate states. In short, they emphasize population
and community dynamics rather than the structure and pattern that was
addressed by many of the other authors. These models are remarkably powerful,
and explain effects apparent in many fish populations, but we can only join
Persson and De Roos(this volume) in concluding that ‘a major challenge...is to
develop approaches that allow the analysis of more complex configurations in
terms of the numbers of species present’. When even simple real food webs may
contain tens or hundreds of species, this is a challenge indeed.
Several authors referred to the ecosystem consequences of body size, includ-
ing CO 2 production (Petcheyet al., this volume) and nutrient cycling, though this
aspect was most explicitly addressed byHallet al. (this volume). The latter
address the extent to which animals affect nutrient cycling directly, through
ingestion, egestion, production and excretion, and how body size controls such
effects. Partially as expected, nutrient excretion rates scaled allometrically, with
an exponent less than 1. Ammonium excretion of stream invertebrates from
18 taxonomic orders scaled at 0.85 with body mass, though there is an interesting
degree of variation, apparently related to taxonomy and thus also potentially to
the measure of body size used for different taxa. For instance, why are there
differences in the scaling of the excretion of P, but not N, between two species of332 A. G. HILDREWETAL.