Territory Abandonment, Theft, and Recycling by a Lotic Grazer: A Foraging Strategy for Hard Times

Abstract

The foraging behavior of Cricotopus bicinctus (Diptera: Chironomidae) was examined in a highly productive warmwater stream by means of in situ time-lapse cinematography. Larvae that consume periphyton routinely depleted and abandoned feeding territories, which they nonetheless defended during the depletion phase. This behavior resulted in cycles of territory establishment and abandonment with a mean period of approximately 3 h. Larvae in search of territories routinely engaged in aggressive interactions with neighboring territory-holders and occasionally commandeered occupied sites (territory theft). Transient larvae also frequently occupied abandoned sites, reusing the central tube structure and foraging in the same surrounding territory (territory recycling). A depletion-frequency sensitive cost/benefit model of feeding territoriality is developed to examine the relative costs of defense, theft, and recyling. Defense is shown to yield net energy gains when competitor incursions reduce territory depletion times by as little as 2-3%. Territory theft and recyling mitigate the loss of resources to competitors by increasing time available for foraging. We argue that these behaviors are critical additions to the larvae's foraging strategy, which enable them to achieve a positive net energy balance in an energetically marginal foraging environment.