Large-Scale Phenomena in Anti-Predator Behavior: On the Consequences of Putting Predators Back Into Predator-Prey Interactions

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Large-scale phenomena in anti-predator behavior: on the consequencesof putting predators back into predator-prey interactionsPI - Steven L. LimaMost studies on the anti-predator behavior of animals focus on a small area in which prey respond to an ambient level of predation risk imposed by predators. The tendency has been to focus more the behavior of prey rather than predators, and the latter have usually been treated merely as a source of risk to prey rather than active participants in the behavioral interaction. This small-scale perspective has revealed much about behavioral predator-prey interactions, but it has missed an entire class of behavioral interactions that exist at larger spatial scales. To appreciate these large-scale interactions, one must think on the scale of an ecological landscape, or an area many km2 in extent-a scale much larger than usually considered by behavioral ecologists. One must also put predators back into the picture by allowing them to be an active participant in the behavioral interaction. More specifically, the proposed work is motivated by a simple question: what drives the movement of animals across a landscape? The present (small-scale) consensus holds that movement by prey attracts predators, hence movement by prey must reflect a need to find new sources of food, etc. However, the results of a simulation model show that predator and prey may be involved in a large-scale shell game, in which predators move frequently in search of elusive prey, and prey move among feeding sites to remain elusive. Furthermore, if prey in a given area are relatively difficult to locate, then predators will focus their attention elsewhere on more predictable prey, with the result that these predictable prey may initiate greater movement to avoid predators. This indirect interaction among prey (through their effect on the predator's behavior) represents a related large-scale phenomenon: the predator pass-along effect. Under other circumstances, predators might avoid constantly attacking prey at a particular location in an effort to render them more catchable in the long-run. Such predatory behavior represents another large-scale effect: prey management by predators. The further theoretical exploration of these large-scale phenomena is an important feature of the proposed work.Much of the proposed work covers an empirical exploration of these large-scale behavioral interactions. This work focuses on the conceptually important paradigm of the small bird in winter, in which small birds must survive both the rigors of winter and the predatory onslaught of bird-eating Accipiter hawks. This task requires much basic biological research, as very little is known about the large-scale movements of small wintering birds or Accipiter hawks. The daily movements of hawks and their avian prey will be followed (via radiotracking techniques) over study areas many km2 in extent. Basic information will be established on hawk and prey home range sizes and movements. Using food manipulation sites established throughout a study area, the distribution and spatial predictability of prey birds will be altered experimentally. These food sites will be manipulated (established and withdrawn) in order to test predictions concerning shell games, predator pass-along effects, and prey management by predators. Conducting behavioral research at a large spatial scale presents unique challenges, but such work represents an important step in the study of predator-prey interactions, one that may ultimately shed much light on ecological systems in general.