RPG: Tactical Defensibility: Landmarks and Territorial Behavior

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9707464 Eason Many animal species are territorial, with individuals defending areas against conspecifics. Territory owners incur costs from defending the territory, but also benefits from the territory's resources; benefits must outweigh costs for defense to be feasible. Previous work has ignored a characteristic of territories that may be critical in determining the costs of their owners: tactical defensibility, or the relative difficulty of defending a particular site. One factor that may be the primary determinant of defensibility is the presence or absence of landmarks in the habitat. Anecdotal reports from a wide variety of taxa (insects, fish, reptiles, birds, and mammals) have suggested that animals use naturally occurring and man-made features as territorial boundaries. This common phenomenon has received very little attention from scientists, and this study will address this lapse. The system to be studied is the territorial behavior of the cicada killer wasp (Sphecius speciosus). Males of this species defend mating territories on flat, featureless ground. This species responds strongly to landmarks: male wasps will move their territories so that the boundaries coincide with landmarks, if landmarks such as dowels are provided. This study will determine the degree to which the size and shape of territories can be manipulated by introducing landmarks. For experiments, grids will be constructed of dowels, and the size and shape of the units in the grid will be varied. Behavioral data will also be collected. The data obtained will be used to examine the effects of tactical defensibility on defensive costs and male mating success in cicada killers. The results will provide information about the effects of habitat heterogeneity on territory size and thus on the density of males. Such data are of value to theoretical ecologists and in addition will be of practical use to conservation biologists: an understanding of how habitat heteroge neity affects territorial species may enable wildlife biologists to create habitats that are more suitable to threatened or economically important species.