9780521861724htl 1..2

a multivariate (descriptive) setting. Other things being equal, it may be that body

size will be larger in more productive streams (reflecting greater competitive

status of larger species or, more mundanely, a more adequate diet) or in streams

with larger substratum particles (because of the provision of appropriate living

Predators

Invertebrate body size (mm) 0

2

4

6

8

10

12

Figure 5.5Averages (with standard error

bars in mm) for mean (grey bars), lower

(white bars) and upper (black bars) quartile

body lengths of predatory invertebrates

from 18 New Zealand streams in three fish

classes. The middle set of histograms, for

sites containing only brown trout,

indicates that trout are responsible for

reducing body size. Fish icons as in

Figure5.2.

Principal Component 2

-^

16.3% of variation–10

–4

–3

–2

–1

0

1

2

3

4

–8 –6 –4 –2 0 2 4

–10 –8 –6 –4 –2 0 2 4

–4

–3

–2

–1

0

1

2

3

4

Principal Component 1 – 39.7% of variation

–10 –8 –6 –4 –2 0 2 4

(a) Disturbance (b) Algal productivity

–10 –8 –6 –4 –2 0 2 4

–4

–3

–2

–1

0

1

2

3

4

–4

–3

–2

–1

0

1

2

3

4

(c) Substrate size (d) Substrate variability

Figure 5.6Principal components ordination of the proportion of invertebrates in

different size classes, with symbols scaled by values of physicochemical variables:

(a) disturbance, (b) algal productivity, (c) substrate size and (d) substrate variability.

See Table5.1 for units. White circles in (a) indicate no disturbance data.

92 C. R. TOWNSEND AND R. M. THOMPSON