Traditional theories of animal behavior assert that animal conflict within a species is highly ritualized and does not vary from contest to contest. This species-specific model assumes that repetitive use of the same visual and vocal displays and an absence of escalated fighting evolved to prevent injury. The contestant that exhibits the one another and stretching their necks skyward; the tortoise perceived as being "taller" wins.
In populations of the spider Agelenopsis aperta, however, fighting behavior varies greatly from contest to contest. In addition, fighting is not limited to displays: biting and shoving are common. Susan Riechert argues that a recently developed model, evolutionary game theory, provides a closer fit to A. aperta territorial disputes than does the what constitutes winning; in evolutionary game theory, the payoffs are defined in terms of reproductive success.
In studying populations of A. aperta in a grassland habitat and a riparian habitat, Riechert predicts that such factors as the size of the opponents, the potential rate of predation in a habitat, and the probability of winning a subsequent site if the dispute is lost will all affect the behavior of fighting than in the riparian habitat, where 90 percent of the habitat is suitable for occupation.
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