Steven L. Lima - US grants

Virtually all animals are both predators and potential prey for other animals. Inherent in this truism are behavioral "conflicts" such as active feeding vs. minimizing exposure to predators. Behavioral research focused on understanding these conflicts has revealed much about the nature of decision-making by animals. Research on anti-predatory behavior has also yielded considerable insight into the evolution of interactions among species and the workings of large-scale ecological systems. It also promises to shed some light on human behavior, a perspective deserving more attention from researchers. Dr. Lima is studying anti-predatory behavior in a social context. Specifically, his research examines the (very common) group-based systems for the early detection of predatory attack, and the problems that their very existence poses for evolutionary explanations of cooperative behavior. Predator-detection systems based upon the alertness (or vigilance) of individual group members suggest levels of cooperation that would not be expected in supposedly selfish animals. Nevertheless, such behavior is indeed observed. Using a well-characterized bird species, the dark-eyed junco, Dr. Lima will investigate a key, untested assumption underlying current attempts to explain this cooperation: that group members are in some way aware of the vigilance levels of their groupmates. Examining this simple assumption will require a series of behavioral experiments performed under controlled environmental conditions. Preliminary observations suggest that these birds are actually not monitoring the behavior of their flockmates. Should these observations be confirmed experimentally, then a major reassessment of our current understanding of widespread group-based predator-detection systems may well be in order.

9723437 Lima This research is directed at a new understanding of a widespread behavioral phenomenon: the vigilance group size effect, in which socially-feeding animals engage in less vigilance (alertness) with an increase in group size. Despite the fact that this is one of the most well established results in the study of animal behavior, many important issues remain unaddressed and even unrecognized. The proposed experiments are designed to help remedy this situation, and in doing so, will shed light on the reasons why so many types of animals are social in the first place. The proposed research focuses first on an assumption fundamental to all explanations of the group size effect: that an animal cannot detect predators while it is actively feeding with its head down. Recent work suggests that apparently non-vigilant (feeding) birds can detect approaching predator attacks at a considerable distance. A main goal is thus to characterize this ability in birds (as represented by the dark-eyed junco, Junco hyemalis) under realistic situations, and then explore its consequences for the group size effect itself. This proposed work will determine whether the group size effect represents a previously unrecognized interaction between poor quality vigilance (while actually feeding), and high quality vigilance (while overtly alert). The proposed research also explores two unorthodox explanations for the group size effect. The first is based on theoretical developments which suggest that the group size effect occurs only because group sizes change frequently over time (as animals come and go from the group). This idea will be tested by allowing captive juncos to feed in constant group sizes or in groups that vary over time. If the new theory is correct, only those birds experiencing the variable group sizes should exhibit the basic group size effect. The second unorthodox explanation for the group size effect concerns the effect of competition for food on vigilance. This view does not deny that animals are vigilant for predators, but maintains that they decrease their vigilance in larger groups because competition for food is more intense as group size increases. If this view is correct, then the group size effect should be much more pronounced when animals are feeding on a limited food supply; this prediction will be tested in flocks of house finches (Carpodacus mexicanus). Results from this research will allow a better understanding of group behavior and the evolution of sociality.

Large-scale phenomena in anti-predator behavior: on the consequences
of putting predators back into predator-prey interactions

PI - Steven L. Lima

Most 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.