|Monkeys, Apes and Humans
Department of Anthropology, University of Missouri-Columbia
Mating systems may be conceptualized as a compilation of behavioral strategies that individuals in a population utilize to obtain mates. Discussions of mating systems usually include reference to: 1) number of mates acquired by individuals of each sex, 2) manner(s) of mate acquisition, 3) presence of "pair bonds," and 4) patterns of parental care provided by each sex. These four factors are associated in consistent ways referred to as polygyny, monogamy, and polyandry.
The ability of a portion of the population to control the access of others to potential mates is a critical factor determining the mating system. Control can be direct, as in the physical herding of mates and exclusion of others competing for mates. Control of access to potential mates can also be indirect, as in the control of resources critical for either mate attraction or successful reproduction. The greater the degree of control or monopolization, the greater the resulting variance in mating success, and the greater the level of intrasexual competition.
What, then, causes one population (or species) to have one type of mating system, and another population to have a different type?
Environment -----> Mating system
Ecological constraints impose limits on the degree to which sexual selection operates (within phylogenetic constraints). Two variables seem critical: 1) distribution of resources, and 2) distribution of mates.
If resources are distributed uniformly in the environment, then there is little opportunity for resource monopolization, and polygamy based on resource control will be difficult. On the other hand, if resources are unevenly distributed, the potential for obtaining additional mates increases because some individuals may be able to control a larger quantity or better quality of resources than others. If mates are clumped (perhaps because of a localized resource), then defense of multiple mates may be possible. The assumption that increased male PI results in lowered reproductive variance as a absolute rule is false.
The temporal distribution of mates can also affect the mating system. If females become sexually receptive in unison (a short mating season), there is little potential for individual males to monopolize multiple females. If the time involved in acquiring a single mate is a significant portion of the total time that mates are available, trends toward polygamy will be minimal.
Emlen and Oring (1977) derive the following "ecological classification" from the above principles:
Read Chap. 7 !!!
Department of Anthropology
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