Mating Systems - An Introduction to Behavioural Ecology - page 259

Females social: range defensible by male
Where females occur in small groups in a small range, then a single male may be able to
defend them as a permanent harem within his territory (e.g. black and white colobus
Colobus guereza , Hanuman langurs Presbytis entellus ). When a new male takes over the
territory, he often kills the young offspring fathered by the previous male, thus bringing
the female into oestrus sooner and hastening the day he has a chance to sire his own
young (Hrdy, 1977). Where females occur in larger groups several males (often relatives)
may defend the territory together (e.g. red colobus Colobus badius , chimpanzees, lions).
Joint defence by several males may increase the length of tenure of a harem and may
also be necessary for economic defence of large groups of females wandering over a
large range (Bygott et al ., 1979).

Females social: range not defensible by male
Sometimes groups of females wander over ranges which are uneconomic for one or
more males to defend. The ways in which males compete for females then depend on
how predictable female group movements are in time and space.

(a) Daily female movements predictable . Sometimes the group of females wanders over a
large range but uses regular routes to particular water holes or rich sources of food.
In these places the males may defend small territories, much smaller than the females'
range, and attempt to mate with them as they pass through (e.g. topi Damaliscus
lunatus korrigum , Grevy's zebra Equus grevii ). Such defence of mating territories may
occur where more direct competition between males, such as fights for harems,
would be costly because males are unable to build up the food stores necessary for
them to engage in intense male-male interactions (Owen-Smith, 1977).
(b) Daily female movements not predictable . Here males tend to follow the females, rather
than waiting for the females to come to them. Where females live in small groups
males may rove and associate with individuals in oestrus (e.g. mountain sheep Ovis
canadensis , elephants Loxodonta africana ). Where female groups are larger, the males
may attempt to defend harems. Harems may be seasonal or permanent.

Sometimes males
wait for females

Sometimes males
follow females

Seasonal harems . If all the females come into oestrus at a particular season, then it
may pay a male to put on energy reserves to enable him to have a burst of energy
expenditure on harem defence. For example, male red deer ( Cervus elaphus ) stags
compete to defend harems during the one month in which all females come into
oestrus. A male's reproductive success depends on his harem size and the length of
time for which he can defend the harem and this, in turn, depends on his body size
and fighting ability. After the mating season the males are reduced to very poor body
condition and are literally 'rutted out'! (Clutton-Brock et al ., 1982).

As another example, female Northern elephant seals ( Mirounga angustirostris ) haul
up on beaches to drop their pups and mate again for the production of next year's
offspring. Because the females are grouped, due to the localized nature of the
breeding grounds, they are a defendable resource and the males fight with each
other to monopolize them. The largest and strongest males win the biggest harems
and in any one year all the matings are performed by just a few males (Le Boeuf,
1972, 1974; Cox & Le Boeuf, 1977). To be a harem master is so exhausting that a

Harem defence