community-scale patterns of production in temperate streams: (1) trophic
resource demand scales as M0.75, (2) resources are used at equal rates by members
of each body-size class, and (3) N is maintained at an equilibrium density (Brown
et al., 2004). Our finding is particularly relevant to studies of stream productivity
because it suggests that, within temperate-stream communities, the interaction of
individual body mass and metabolism and population abundance results in levels
of secondary production that are essentially constant across the entire spectrum of
body sizes occurring within macrofaunal communities. In comparison with the
temperate stream communities, the overarching hypothesis of metabolic theory
was rejected for the snag-dwelling community of the Ogeechee River, indicating a
fundamental difference between community structure and function between
stream types. This finding should stimulate the formulation of questions con-
cerning processes underlying differences between body size and the secondary
production of stream communities and demonstrates the strength of the theoret-
ical framework of Brownet al.(2004) as an investigative tool.
We conclude by briefly considering the ‘predictive’ power of the metabolic
theory of ecology, and its application to studies of ecological productivity. The
empirical relationships that form the grist for current metabolic theory (e.g.
Brownet al., 2004) do have relatively high predictive power in the sense that
scaling exponents produced using data sets integrating numerous and often
phylogenetically diverse taxa representing a large range of body sizes vary little
among different data sets. Analyses of data sets representing a smaller number of
closely related taxa (e.g. different orders of benthic insects), however, may show
exponents that diverge radically from predictions (e.g. Benke, 1993 ; Morin &
Dumont, 1994 ). Further, even within single communities, the range of residual
variance of the dependent variable for typical plots of N, B, P/B or P against M for
specific taxa may range over several orders of magnitude (Figs.4.7&4.8). It
remains unclear whether these exceptions are true departures from metabolic
theory or are attributable to systematic factors, such as a low signal-to-noise
ratio, that occur when the range of body size used in analyses is constrained.
Given this level of uncertainty, the predictive power of metabolic theory for
determining production statistics (i.e. P, P/B) for single populations or even
communities is of dubious value. The predictive power of metabolic theory
does hold great promise for identifying important questions about general
relationships between body size and metabolic processes within and across
broad scales of ecological pattern and process.Appendix I A primer on secondary production and the P/B
Production is generally defined as the formation of biomass through time
(Benke, 1993 ; Benke & Huryn, 2006 ). It is essentially the increase of an indivi-
dual’s mass over time scaled to the population or community levels of ecological68 A. D. HURYN AND A. C. BENKE