Biology Reference
In-Depth Information
male usually only manages to be top ranking for a year or two before he dies. In the
process of defending his harem against other males he sometimes tramples on his
females' new-born pups. Although this is obviously not in the females' interests,
these pups were probably not sired by the male himself because he is unlikely to
have been a harem master the previous year. From the male's point of view,
therefore, there is little cost in damaging or even killing the pups; his main concern
is to protect his paternity.
Permanent harems
. Where females do not all come into oestrus at a particular time,
males may defend permanent harems for the whole duration of their reproductive
life (e.g. hamadryas baboons (
Papio hamadryas
) and gelada baboons (
Theropithecus
gelada
), Dunbar, 1984; Burchell's zebra (
Equus burchelli
), Rubenstein 1986). Often
several groups (male plus harem) go around together forming a large 'super-
group'. Where females go around in still larger groups, several males may associate
with large groups of females and compete with each other for matings. Such
'multimale' groups occur in buffalo,
Syncerus caffer
, and olive baboons,
Papio anubis
(Altmann, 1974).
Leks and choruses
In the examples discussed so far, males compete for females directly (female defence) or
indirectly by defending resources to which females are attracted (resource defence). In
some cases, by contrast, males aggregate into groups and each male defends a tiny
mating territory containing no resources at all - often the territory is no more than a
bare patch of ground just a few metres across. The males put a great deal of effort into
defending their territories and advertise themselves to females with elaborate visual,
acoustic or olfactory displays. In these mating systems, known as leks, females often
visit several males before copulating and appear to be very selective in their choice of
mate. Mating success is strongly skewed, with the majority of matings performed by a
small proportion of males on the lek (Fig. 9.4).
Leks have been reported for seven species of mammals - the walrus, hammer-headed
bat and five ungulates - and some 35 species of birds, including three shorebirds, six
grouse, four hummingbirds, two cotingas, eight manakins, eight birds of paradise, the
kakapo and great bustard (Oring, 1982). This breeding system is, therefore, not
common. Similar systems occur in some frogs (Wells, 1977) and insects (Thornhill &
Alcock, 1983), where females visit male groups, choose a mate and then lay eggs away
from the display site.
It has been suggested that leks occur when males are unable to defend economically
either the females themselves or the resources they require (Bradbury, 1977; Emlen &
Oring, 1977). This may arise where females exploit widely dispersed resources and so
have large, undefendable ranges, or because high population density, and thus high
rates of interference between males, precludes economic female or resource defence.
Thus, in both antelope and grouse, the lekking species are those with the largest female
home ranges (Bradbury
et al
., 1986; Clutton-Brock, 1989) and in Uganda kob, topi and
fallow deer, males lek at high population density but defend resource-based territories
or harems at low density, where defence of females is presumably more economic.
Leks are
aggregations of
males on small
mating territories
Leks may occur
when neither
females nor
resources can be
defended
economically
