Uncharted Territories: Defense of Space in Crustacea

Abstract

Territoriality is a special case of resource defense, in which space is actively defended for exclusive use. As active defense is likely to be costly, territoriality is expected only when the benefits of exclusivity outweigh these costs. In most territorial species of noncrustacean taxa, the defended space includes resources critical for reproduction or food. These resources are not only critical for reproductive success, but also are vulnerable to “looting”, that is, the value of these resources may be reduced through short-term intrusions, even without loss of ownership, thus providing an advantage for active defense of exclusive space. Many crustaceans defend space, particularly burrows or other shelters that are refuges from predation or environmental stressors. While protection is obviously a critical resource, it is not a resource that necessarily requires exclusivity; indeed, many crustaceans that depend upon shelters for protection do not defend them for exclusive use. Nonetheless, many crustacean taxa aggressively defend exclusive access to their shelters. Crustaceans, then, may be especially suitable for testing alternative hypotheses of territoriality, including the potential benefits of interindividual spacing rather than defense of space per se. It is also worth considering a null hypothesis for territoriality: aggressive defense of space in crustaceans may be an artifact of relatively sedentary species with high intraspecific aggression favored in other contexts, rather than aggression favored for defense of particular resources. In addition to these questions, much remains to be learned about territorial behaviors in crustaceans. Most notably, the boundaries of defended space are unknown in many taxa. Understanding the boundaries of defended space is important for understanding the ecological consequences of territoriality, as well as aspects of territory acquisition and the roles of neighbor relationships and territorial advertisement signals in territory defense. Many crustacean territories appear to differ from those described for other animals, especially terrestrial species; it is not clear, however, whether these differences are due to differences in function or habitat, or rather result from our incomplete knowledge of crustacean territoriality.