Does interspecific territoriality reflect the intensity of ecological interactions? a theoretical model for interspecific territoriality

In many studies, interspecific territorial behaviours among co-existing species have been used to infer the presence and the intensity of underlying ecological interactions between species, mainly resource competition. However, the theoretical background of this inference is insufficient. Hence, we constructed a simple theoretical model of interspecific territoriality assuming that interspecific territorial defence is the optimal behaviour. We discuss the factors promoting interspecific territoriality and the relationship between interspecific territoriality and ecological interactions. The model predicts that: (1) a territory holder preferentially excludes intruders of species with high 'exclusion efficiency'; (2) the decision by the territory holder to exclude a certain species or not does not depend on the probability of finding intruders of the species or on the number of intrusions by the species; and (3) interspecific territoriality does not always reflect the intensity of ecological interactions between species. These results indicate that the observation of interspecific territoriality does not necessarily indicate the intensity of ecological interactions. In addition, if territory holders defend their territories as predicted by the present optimal model, the co-existence of competing species is promoted.