0851996159

246 R. Poulin

60

50

40

30

20

10

0

0123456

Effect of parasites on host behaviour

Frequency

n = 107

5 4 3 2 1 0

0 0.1 0.2 0.3 0.4 0.5 0.70.6

Effect of parasites on transmission

Frequency

n = 16

Fig. 12.1. Frequency distributions of effect sizes of helminth parasites on the

behaviour of their intermediate host (top) and of effects of helminths on predation of

the intermediate host by the definitive host, or transmission success (bottom). Data

are derived from published values. Effect sizes of helminths on host behaviour are

the absolute value of the difference in mean behaviour between infected and

uninfected hosts, corrected for sample size and variability; values smaller than 0.5

are considered relatively small effects (Cohen, 1988). The effects of helminths on

predation rate on the intermediate host by the definitive host are computed as the

proportion of infected intermediate hosts eaten minus the proportion of uninfected

hosts eaten; with a maximum value of 1, any value greater than 0.2 indicates a

substantial benefit for the parasite. (Data are from Poulin, 2000.)