9780521861724htl 1..2

Log (predator mass/prey mass)

–2

–1

0

1

2

3

4

5

6

7

–10

–5

0

5

10

15

(c)

Species

averaging

(e)

All

individual links

(f)

Individual

predator

(n = 99)

(d)

Averaging

by links

(a)

Freshwater

(b)

Marine

Figure 6.5Distribution of predator:prey body-mass ratios for feeding links in aquatic systems.
Boxplots (a) and (b) show species-averaged consumer-resource ratios for species pairs taken from
the Broseet al.(2005) data set, for freshwater and marine food webs, respectively. The adjacent
boxplots (c)–(f) in the lower panel show the effects of averaging at different scales of resolution
within the Broadstone Stream food web. Boxplot (c) depicts the species-averaged values for the
Broadstone Stream food web, as taken from the community matrix and the summary trivariate
plot. Boxplot (d) depicts species averaging by links (i.e. the average body mass of consumers and
that of the prey found in their guts for each species pair – thus this includes only individuals
involved in a predation event, such that each link is a mean of the consumer-resource ratio of the
two protagonist species involved). Boxplot (e) shows values from all individual predation events.
Note that the trivariate plot understimates the true consumer-resource size disparity by about
one order of magnitude – thus the predators are feeding on a subset of the prey size spectrum. At
the finest scale of resolution (i.e. within-individual distributions), the right-hand boxplot (f) shows
the distribution of prey body masses from the gut of a single predator within the Broadstone
Stream food web (n¼99 prey individuals of 13 species).