it. This is true because residents invest a great deal of energy and time into mastering their area and resources and may well have dependent young. A challenger is devoid of these properties and thus has nothing to lose (Gosling, 1982).
Age is virtually never the sole criterion for achieving dominance or acquiring territory. However, there is likely to be a strong association with age because of two factors. First, the territory holder almost always triumphs in one-on-one encounters. Therefore, territory holders often have held their territories for a long time and thus tend to be older. Second, there is a positive relationship between age and dominance of subordinates, who are continually competing for "next-inline" status.
Learning, defined as any change of behavior of individuals due to experience (Cavalli-Sforza and Feldman, 1981; Alcock, 1993), is found in virtually all animal species from the simplest bacteria and protozoa to complex mammals, such as cetaceans, primates, and elephants. The mechanisms of learning can occur at different levels. Self-teaching occurs when a young individual eats a food that tastes bad and subsequently avoids it. Birds acquire songs and repertoires through imitation. Teaching occurs when inexperienced young of predator species accompany their parents on a hunt to acquire skill. The cumulative learning experiences of groups constitute unique cultures that can often be transmitted from one generation to the next (Alcock, 1993). It is widely believed that selection favors specific learning abilities as solutions to specific ecological problems (Alcock, 1993). For example, solitary animals gain useful flexibility by adjusting their diets to whatever nourishment is available. Also, many animals that hoard food must remember where their food cache is located. The ability of social animals to adjust to the behavior of others (e.g., who is dominant to whom, what one individual did to another individual, etc.) may greatly affect their reproductive success (Alcock, 1993). Information that can only be transmitted through learning includes home range, migratory pathways, location of food sources, tool construction and use, acceptability of food items, parental-care skills, and social relationships, such as pair bonding and alliances (Bonner, 1980).
Although there are few papers published on the elderly in nature, the biological literature contains a surprising amount of information on nonhuman elderly that has never been compiled and synthesized. The life history and field biology of a large number of endangered or economically important species in all major taxonomic groups has been studied and documented in meticulous detail. This includes longitudinal studies of marked individuals or monitoring, for decades,