Evol Ecol Res 6: 765-775 (2004)     Full PDF if your library subscribes.

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

Osamu K. Mikami1* and Masakado Kawata2

1Department of Ecology and Evolutionary Biology, Biological Institute, Graduate School of Science and  2Division of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Aoba-ku, Sendai 980-8578, Japan

Address all correspondence to Osamu Mikami, Department of Biology, Faculty of Science, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
e-mail: omikascb@mbox.nc.kyushu-u.ac.jp


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.

Keywords: ecological interaction, foraging theory, theoretical model, interspecific competition, interspecific territoriality, optimal behaviour, species co-existence.

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