Territoriality

Territoriality is the occupation and defense of a particular area. In the account developed here, it has two connected but distinct explanations: it can be an evolutionarily stable response to the asymmetry between a resident and an intruder, and it can regulate access to breeding without having evolved for the good of the population. The decisive question is not merely what a territory appears to accomplish, but whose reproductive prospects the behavior serves and how the strategy holds its place against alternatives.

Territoriality as a Conditional Strategy

In the analysis of evolutionary strategies, the resident–intruder distinction supplies an asymmetry that can make territorial defense stable. A population in which the intruder wins and the resident retreats would encourage individuals to avoid being residents. To secure the intruder’s advantage, they would have to keep moving; the resulting costs in time and energy would make the strategy self-defeating. By contrast, if residents tend to win and intruders retreat, individuals benefit by remaining on a particular piece of ground. The behavior then looks like defense, but it can arise through selection for a stable conditional rule rather than through a benefit to the group as a whole.

Niko Tinbergen’s stickleback experiment illustrates how directly the rule can depend on location. Two male sticklebacks had built nests at opposite ends of a tank, and each defended the area around his nest. Tinbergen placed the males in large glass test-tubes and held the tubes next to each other, so that they could attempt to fight through the glass. Near male A’s nest, A adopted an attacking posture and male B attempted to retreat. When Tinbergen moved the tubes to male B’s territory, their roles reversed. Moving the enclosed fish from one end of the tank to the other changed which male attacked and which retreated. The result fits a simple conditional strategy: attack when resident; retreat when intruding.

This account also shifts the kind of explanation territoriality requires. The question of what biological advantage a territory provides may be unnecessary in cases where the behavior follows from the timing asymmetry of arrival at a patch of ground. The resident’s position and the intruder’s arrival can be enough to sustain the pattern: individuals following the locally successful rule reinforce the convention that the resident stays and the newcomer yields. Territorial defense, on this reading, is not proof that animals consciously calculate ownership or intend to manage a population. It is a behavioral pattern that can persist because alternatives do worse in the circumstances that define the encounter.

Territories and Access to Breeding

Territoriality also enters the debate over whether animal populations regulate reproduction for the common good. Wynne-Edwards proposed that social behaviors, including territoriality and dominance hierarchies, help limit population growth. The disagreement is not over whether birth rates are regulated, but over how the regulation evolved: as restraint benefiting the group, or through strategies that benefit the reproducing individual.

Territories vary in what they contain. For a breeding pair of robins, a territory can be a large area of woodland that serves as the principal foraging ground. For herring gulls, it can be a small area with a nest at its center and no food. Wynne-Edwards interpreted some territorial contests as competition for a token prize rather than for a material resource. In many cases, females refuse to mate with males that have no territory; if a female’s mate is defeated and his territory taken, she may attach herself to the victor. Even apparently faithful monogamy can therefore be understood, in this account of Wynne-Edwards’s theory, as attachment to the territory rather than to the individual male.

If the number of territories is finite, territory ownership limits who breeds. Individuals that fail to obtain a territory may not reproduce, making possession resemble a licence to breed. Red grouse appeared to provide a particularly striking instance: birds that lost the early-season contests became outcasts, did not breed, and mostly starved by the end of the season. At first sight, the losers’ apparent cessation of competition could seem like voluntary restraint that leaves the successful breeders undisturbed.

The same observations, however, admit an individual-level explanation. A non-territorial red grouse is physically capable of breeding: when a territory holder is shot, an outcast can promptly take the vacant place and breed. Renewed fighting may therefore not be the best available option. If the chance of succeeding to a territory when its owner dies is better than the chance of taking it by force, conserving energy and waiting may offer the individual a better prospect. What appears to serve the group as a reserve of replacements can also be a waiting strategy that benefits the outcast, even if it ultimately fails to produce descendants.

Limits and Interpretive Stakes

The discussion treats Wynne-Edwards’s account as plausible in appearance but weakly established by the evidence: many examples that can be read as group-benefiting restraint can also be explained in selfish-gene terms. Territoriality is one such contested case. Its population-level effect—restricting breeding to individuals with territories—does not by itself establish that it evolved to control population size. The difference lies in the proposed cause: a group-benefit explanation versus an individual’s conditional strategy for securing or eventually obtaining a chance to breed.

The distinction matters because observed restraint is not enough to identify its evolutionary function. An animal that stops challenging a territory holder may appear to accept a collective rule, yet waiting can make sense if renewed conflict is costly and a vacancy may arise. Conversely, a territory can act as a practical gate to reproduction regardless of whether that outcome was selected for as population regulation. Territoriality therefore connects the mechanics of local contests to a broader methodological caution: consequences that benefit a group should not be mistaken, without further evidence, for the reason a behavior evolved.