Individual distance in crustacea II. the mantis shrimpGonodactylus oerstedii

An Effect of Landmarks on Territory Shape in a Convict Cichlid

We determine size, shape and location for a territory that is optimal in the sense of minimizing defense costs, when a given proportion of the boundary is landmarked and its primary benefit in terms of fitness is greater ease of detecting intruders across it. Increasing the landmarked proportion of boundary causes the optimal configuration to be smaller and more elongated, and to be located with its center further from the nest, so that the nest is closer to the landmarked boundary. These predictions accord with observations in a recent study of the convict cichlid Amatitlania siquia. Our results thus confirm the consistency of the observed behavior with the hypothesis that A. siquia designs its territory to make intruders easier to spot. Our results also lead us to conjecture that moving the landmark proportionately closer to or further away from the nest would have yielded essentially the same outcome in this study, because the optimal configuration depends only on the angle subtended by the landmark at the nest and hence only on the length of the landmark relative to its distance from the nest, as opposed to its absolute value.

Landmarks in territory partitioning: a strategically stable convention?

A convention is a rule based on arbitrary cues that allows quick resolution of potentially protracted disputes. A familiar example is the Bourgeois strategy, in which the second of two animals to discover a resource yields it to the first, even though it may be stronger than its opponent. Here we develop a game-theoretic model to show that neighbors with imperfect information about one another's fighting abilities can be favored to accept a landmark as the designator of a territory boundary, even when the resulting territory is smaller than the one that would have been won through fighting. Thus, the use of landmarks or other mutually obvious solutions can serve as a convention for territory partitioning. For a distribution of fighting ability with low variance and high skew, there is a remarkably high probability that an animal will accept a smaller territory than it would have won through fighting. The analysis provides a possible explanation for the observed use of landmarks as boundary markers by territorial animals in a variety of taxa, including birds, fish, insects, and mammals. The analysis also suggests why territory boundaries are stable, once established, despite changes in characteristics of the residents or the environment.