value of the actual trophic efficiencies and the relative sizes of predator and
prey, the relationship of both N and B vs. M may be altered (e.g. N/M0.75!
N/M1.0;B/M0.75!B/M^0 ; Brown & Gillooly, 2003 ) which will have con-
sequences for P vs. M (e.g. P/M0.25rather than M^0 when B/M^0 ).
Considering that the scaling exponents for B and N vs. M for the Ogeechee River
were not significantly different from1 and 0, respectively (e.g. Fig. 4.3), the
expectation of a scaling exponent substantially<0 for P vs. M seems reasonable.
On the other hand, there appears to be little substantive support for this explan-
ation of the difference between scaling exponents among the temperate streams.
The relationship between trophic position and M was plotted for the taxa occurring
in each of the four stream communities, based on general knowledge of feeding
habitats of their fauna for the three temperate streams, and actual gut analysis for
members of the snag community of the Ogeechee River (Benke & Wallace, 1997 ;
Benkeet al., 2001;Fig.4.9). A comparison of the resulting plots shows that a rather
broad spectrum of body size is apparent for primary and secondary consumers in
all communities, with little indication of a greater correlation between body size
and trophic position in the Ogeechee River than for the temperate streams.
Another major factor to consider in an attempt to explain the discrepancy in
scaling of P/B vs. M among stream communities is the ecological characteristicslog10annual P/B–0.50.00.51.01.52.02.5–0.50.00.51.01.52.02.5–0.50.00.51.01.52.02.5–0.50.00.51.01.52.02.5Ball Creek
log 10 P/B = 1.07 – 0.18 log 10 M
(r^2 = 0.25, p < 0.0001)Ogeechee River
log 10 P/B = 2.14 – 0.41 log 10 M
(r^2 = 0.51, p < 0.0001)Sutton Stream
log 10 P/B = 1.39 – 0.27 log 10 M
(r^2 = 0.35, p < 0.0002)Stony Creek
log 10 P/B = 1.21 – 0.23 log 10 M
(r^2 = 0.32, p < 0.0002)012 3 4 5 6 7 012 3 4 5 6 7012 3 4 5 6 7 012 3 4 5 6 7
log 10 M (∝g)Figure 4.8Log-log plots of
annual P/B (yr^1 )againstM
(individual taxa,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.66 A. D. HURYN AND A. C. BENKE