9780521861724htl 1..2

of the Ogeechee snag-habitat itself. A significant proportion of the production of

the snag community is subsidized by organic seston (suspended particles) that is

continuously delivered from habitats upstream. This high-quality and abundant

food source supports exceedingly high densities of filter-feeding organisms on

the snags (Benke & Parsons, 1990 ; Benke & Wallace, 1997 ; Benke, 1998 ). This is

reflected, to some degree, by the high densities of small organisms in the

Ogeechee River community compared with the temperate streams (Figs.4.2&

4.7). Other types of primary consumers, however, must browse organic matter

directly from the surface of the snag (Benke & Jacobi, 1986 , 1994; Benke, 1998 ).

Differences in resource quality and supply rate, along with the relative meta-

bolic costs of radically different feeding strategies, could potentially cause scal-

ing exponents to depart from predicted values due to a confounding effect of

source of food (e.g. seston vs. biofilm) and body size. Knowledge of the compa-

rative bioenergetics of these different feeding guilds, and whether these are

confounded with the size-distribution of the integrated snag community, is

required to assess this hypothesis properly.

In summary, the overarching hypothesis of metabolic theory, that the common-

ality of metabolic processes across scales from cellular to ecosystem explains the

relationship between body size and N, B, P and the P/B, was clearly not rejected for

our sample, albeit small, of temperate-stream communities. This finding suggests

that the following conditions may be of primary importance in determining

trophic level or position

1

2

3

4

1

2

3

4

Ogeechee River Ball Creek

012 3 4 5 6 7 012 3 4 5 6 7

1

2

3

4

1

2

3

4 Sutton Stream Stony Creek

012 3 4 5 6 7 012 3 4 5 6 7

log 10 M (∝g)

Figure 4.9Plots of annual trophic

level or trophic position against

log 10 M (individual taxa,mg/

individual) for four stream

communities (see Fig.4.2for details).

Trophic position (sensuBenke &

Wallace, 1997 ) for taxa from the

Ogeechee River was estimated on

the basis of gut content analysis.

Trophic level for taxa from the

remaining three communities was

presumed on the basis of published

feeding habits and limited gut

analysis.

BIOMASS TURNOVER AND BODY SIZE 67