9780521861724htl 1..2

Brown, Allen & Gillooly, this volume). This conceptual framework (i.e. the

‘metabolic theory of ecology’; Brownet al., 2004) provides a number of specific

predictions about the relationship between body size and bioenergetic variables

over a wide range of ecological scales. In this paper we test selected predictions

that relate to the relationship between body size and P/B for stream animal

populations and communities. We chose to focus on the P/B because it is a

powerful variable that summarizes the dynamic relationship between growth

rate, biomass and production (AppendixI).

The predictions

We used detailed community-level production budgets for four streams

(described below) to test a priori predictions about the relationship between

body size (M, mg ormg dry mass (DM) or ash-free dry mass individual^1 )and

population density (N, no. individuals m^2 ), biomass (B¼MN, mg m^2 ), produc-

tion (P, mg dry mass or ash-free dry mass m^2 yr^1 ), and the P/B (yr^1 ). We chose to

analyze the relationship of each of the major production variables (N, B, P) with

body size because they all interact to contribute to the ultimate relationship of

body size with P/B (AppendixI). As will be seen, each of the predictions described

below is derived from the theoretical framework proposed by Brownet al.(2004).

Prediction 1

Density (N, number of individuals m^2 ) will decrease as body mass increases

(M, mg individual; Fig.4.1). Some previous studies (e.g. Brownet al., 2004;

Woodwardet al., 2005a) have indicated that N/M0.75when the relationship

is fitted to a power curve using least-squares regression. This relationship is

expected if the following conditions are met: (1) requirement for resources by

individuals scales as M0.75, (2) population size increases until limited by resour-

ces (i.e. equilibrium density), and (3) total resource use will be independent of

M because resources are used at equal rates by members of each size class within

a given population (Brownet al., 2004).

0

1

123456

2

3

4

5

6

7

log abundance (N, individuals m

–2)

log biomass (B, mg m

–2)

log production (P, mg m

–2

yr

–1)

log P/B (P/B, yr

–1)

body size (M, mg individual–1)

B ∝ M0.25

P ∝ M^0

P/B ∝ M –0.25

N ∝ M –0.75

Figure 4.1Predicted relationships

between individual body mass and area-

specific abundance, biomass, production

and the P/B. The predictions follow

Brownet al., 2004.

56 A. D. HURYN AND A. C. BENKE