Competing for Resources - An Introduction to Behavioural Ecology - page 134

were removed from the chorus, then
the small males began to call. If calls
were broadcast from a loudspeaker,
then large males came over to attack
the speaker while small males became
satellites next to it.
How do satellites decide which callers
to parasitize? Observations showed
that when two males were together,
one calling and the other a satellite,
then they had about an equal chance
of capturing the female. (Overall,
callers did better because not all callers
had satellites.) If a satellite gains 50%
of a caller's females, and attraction of
females depends simply on call
intensity, then a male's decision rule is predicted to be: 'become a satellite on my
neighbour if his call is at least twice as loud as my own'. Fig. 5.11b shows that 89% of
males adopted the behaviour predicted by this simple rule.
Therefore caller and satellite are two tactics within the conditional strategy 'call above
threshold x, sneak below x', where the threshold depends on the male's body size (and
hence call loudness) relative to that of his competitors. This is an example of case (a) in
Fig. 5.9; satellites (scroungers) are poorer competitors, nevertheless, they maximize their
chance of gaining a female by their choice of which callers (producers) to parasitize.
There are many examples in nature like this, where poorer competitors have to choose
alternative tactics to make the best of a bad job. For example, small male elephant seals
attempt to sneak matings while a large male is busy defending other females in his
harem. Male horseshoe crabs, Limulus polyphemus , in poor body condition attempt to
sneak fertilizations while a female is spawning with a guarding male (Fig. 5.12).
When small body size is correlated with age, individuals may change to more profitable
tactics when they become older and stronger. A male toad or seal, for example, may
change tactics depending on its assessment of competitor intensity. In some cases,
however, body size is fixed throughout an individual's lifetime and reflects feeding
success in the immature stages. Here, a poor quality competitor may have to make the
best of a bad job throughout its lifetime. An example is the bee, Centris pallida , where the
largest males, which had good food as a larva, are three times the mass of the smallest
males, who had poor larval food. Large males fight to gain access to virgin females just
as they emerge from the ground. Small males, who are poor fighters, have to settle for
the less profitable tactic of searching for the few airborne females who have emerged
unmated (Alcock et al ., 1977).

Fig. 5.12 A satellite male horseshoe
crab (left) next to a female (front) and
guarding male (behind). From Brockmann
et al . (1994) and Brockmann (2002).

Satellite males
make adaptive
choices
concerning which
callers to
parasitize

Tactics may vary
with age,
condition or body
size

Morphological switches with body size: dung beetles and earwigs
In some cases the alternative tactics of a conditional strategy involve morphological
specializations. Male dung beetles in the genus Onthophagus come in two morphs: large
males ('majors') have long horns on their heads while small males ('minors') are
hornless (Fig. 5.13a). The development of horns is facultative and depends on the