9780521861724htl 1..2

Constant

Fast variation

Slow variation

(b)

–6.5 –6.0 –5.5 –5.0 –4.5 –4.0

Log 10 (Cell mass (mg))

2.5

3.0

4.0

4.5

3.5

Log

(Density per ml) 10

2 species

4 species

6 species

8 species

(a)

–6.5 –6.0 –5.5 –5.0 –4.5 –4.0

Log 10 (Cell mass (mg))

2.5

3.0

4.0

4.5

3.5

Log

(Density per ml) 10

Figure 13.6Relationships between total density and average cell size of the individuals

in a community in analysis three, coded by (a) species richness and (b) environmental

fluctuations. Arrows show the communities in Fig.13.3that have unusually high

(>1mg ml^1 ) total biomass.

Table 13.4Summary of analysis one of the community consequences of body size

on total community biomass. The response variable is total community density.

M¼body mass, S¼species richness, E¼Experiment 1, E2¼Experiment 2,

E3¼Experiment 3.

ANOVA table

Df Sum sq Mean sq F value Pr(>F)

M 1 82.631 82.631 1369.7640 <2.2e16***

S 1 3.085 3.085 51.1433 1.923e10***

E 2 3.058 1.529 25.3445 1.638e09***

S:E 2 0.828 0.414 6.8662 0.001655**

Residuals 93 5.610 0.060

Coefficients

Estimate Std. error t value Pr(>|t|)

(Intercept) 0.37009 0.24455 1.513 0.1336

M 0.91873 0.03881 23.670 <2e16***

S 0.12799 0.05476 2.337 0.0216*

E2 0.13487 0.23196 0.581 0.5624

E3 0.74098 0.28869 2.567 0.0119*

S:E2 0.06112 0.05607 1.090 0.2786

S:E3 0.12586 0.05855 2.150 0.0342*

CONSEQUENCES OF BODY SIZE IN MODEL MICROBIAL ECOSYSTEMS 257