9780521861724htl 1..2

small body size (e.g. M< 25 mg DM) may range over several orders of magni-

tude, there is little doubt that taxa within this size range are capable of genera-

ting among the highest rates of biomass turnover reported for eukaryotes.

Although often overlooked in studies of community production, due to small

body size and low population biomass, the identification and quantification of

the P/Bs of such taxa is crucial to understanding the dynamic attributes of

food web links (Benke & Wallace, 1997 ; Woodwardet al., 2005b; Steadet al.,

2005 ). The factors controlling rates of biomass turnover are myriad, but aside

from food quality and supply the two most influential factors are probably

temperature and body size. A number of studies based on empirical approaches

have explicitly demonstrated the positive effect of temperature (Benke, 1993 ;

Morin & Dumont, 1994 ) and the negative effect of body size of fresh-

water invertebrates (Banse & Mosher, 1980 ; Benke, 1993 ; Morin & Dumont,

1994 ; Plante & Downing, 1989 ; Morin & Bourassa, 1992 ) on time-specific biomass

turnover rates.

Mechanistic explanations for the relationship between P/B and food quality

and temperature are obvious; explanations of the relationship between P/B and

body size are not. Numerous and diverse explanations have been suggested, but

none is yet universally accepted, greatly complicating the theoretical basis for

–0.3

0.7

01234567 01234567

01234567 01234567

1.7

2.7

–0.3

0.7

1.7

log2.7

annual P/B 10

Ogeechee River

log 10 P/B = 2.46 – 0.50 log 10 M

(r^2 = 0.89, p < 0.001)

Sutton Stream

log 10 P/B = 1.50 – 0.26 log 10 M

(r^2 = 0.86, p < 0.003)

Stony Creek

log 10 P/B = 1.31 – 0.27 log 10 M

(r^2 = 0.81, p < 0.006)

log 10 M (∝g)

Ball Creek

log 10 P/B = 1.22 – 0.24 log 10 M

(r^2 = 0.75, p < 0.006)

–0.3

0.7

1.7

2.7

–0.3

0.7

1.7

2.7

Figure 4.5Log-log plots of

annual P/B (yr^1 ) against M

(mg/individual) for four

stream communities (see

Fig.4.2for details). The grey

line indicates the predicted

slope of the relationship

between log 10 P/B and log 10 M

(P/B/M0.25). The black line

indicates the slope derived

from least-squares

regression of the data.

BIOMASS TURNOVER AND BODY SIZE 63