Cautious individuals have non-invadable territories, according to an evolutionary mechanistic model

Abstract

Territoriality is widespread in the animal kingdom, but its evolutionary origins are less understood than the movement patterns that generate it. Previous studies attempted to understand the evolution of these movement patterns by assuming that certain movement patterns comprised competing strategies and using evolutionary game theory to find which strategies would provide greater fitness and give rise to evolutionary stability. Four strategies were identified: Cautious, an individual that moves through the landscape avoiding all places where it experienced conflicts with other animals; Common-sense, an individual that avoids areas where it lost conflicts and selects areas where it won conflicts; Paradoxical, an individual that does the opposite of Common-sense; and Daring, an individual that seeks areas where it won conflicts, but is unaffected by loss. Previous models used a combination of individual-based models and algebraic calculations, but they did not incorporate recent developments in mechanistic models. Here, we developed a stochastic individual-based model using fluid dynamics to represent space use and used invasion tests to determine evolutionary stability. Using this model, we tested which (if any) of the previous strategies would be evolutionarily stable in two scenarios: one with inconclusive territorial fights and another without. We found that the cautious strategy was evolutionarily stable, in disagreement with previous literature. Cautious individuals show a more homogeneous use of space, when compared to the other three strategies. Cautious individuals tend to win most resources across the environment, which results in greater fitness than other strategies and allows it to invade populations comprised of any of the others. Daring also invades paradox and common-sense strategies, while paradox invades common sense. There was no qualitative difference between scenarios. We discuss how the evolutionary stability of this strategy depends on whether individuals employ their maximal effort when foraging.