Biology Reference
In-Depth Information
(b)
1.2
(a)
1.0
0.8
0.6
0.4
0.2
0.4
0.6
0.8
1.0
1.2
Subject's call intensity (N/m
2
)
Fig. 5.11
(a) A calling male natterjack toad with a silent satellite male next to him,
waiting to intercept any females that are attracted. Photo © Nick Davies. (b) How a
male natterjack toad decides whether to be a caller or a satellite. The subject's call
intensity is plotted against the call intensity of his nearest neighbour. Males were
predicted to become satellites when their neighbours produced calls twice as loud as
their own calls (the area to the left of the dashed line). The open circles refer to males
who were satellites and the closed circles males who called. From Arak (1988). With
permission from Elsevier.
Don't spend time agonizing over these differences now; they will become clearer once
we discuss some examples which will show why the strategy-tactic distinction is useful.
Tactics within a
strategy
Conditional strategies with alternative tactics
Natterjack toads: callers and satellites
In spring, male natterjack toads,
Bufo calamita
, migrate to ponds and call to attract
females for mating. The calls are very loud; on still evenings they can be heard from over
a mile away and from one metre the call is louder than that legally permitted from a car
engine as heard from the sidewalk! Anthony Arak (1983) broadcast male calls from
loudspeakers and showed that females moved passively down sound gradients towards
the loudest call. Therefore, the largest males, who had the loudest calls, attracted the
most females. Small males, unlikely to make themselves heard in the chorus, adopted
satellite behaviour in an attempt to intercept females on their way to the callers
(Fig. 5.11a). Callers clearly did better than satellites; on average 60% of the males were
callers yet they gained 80% of the matings. Therefore, small males made the best of a
bad job until they grew larger and had louder calls. Nevertheless, they varied their
behaviour depending on the degree of competition from the larger males. If large males
Large male
natterjack toads
are callers, small
males are
satellites
