Time to revisit? A predator's previous successes and failures in prey capture determine its return time to patches.

In a heterogeneous environment containing multiple patches that may deplete and renew, a forager should be able to detect the quality of food resources within and among patches and choose to exploit them to best maximize returns. From the predator's perspective, the behavioral responses of the prey in a patch will be perceived as depletion when they retreat to refuge and renewal when they reemerge. A predator encountering responsive prey should manage predation risk, and thus behavioral resource depression, by optimally timing its return time to the patch based on prey behavior. We evaluated the foraging decisions of a predator that encountered patches differing in size of the refuge and prey density. We used little egrets and goldfish as predators and prey in an environment that contained three patches (pools). We manipulated prey density and refuge size and availability (using covers) and observed predator foraging behavior. When the egret had previously caught a fish it did not discriminate between the pools, and the return time was similar for all cover types. The fish densities also did not affect the egret decisions to return to pools. However, when it failed to catch fish, it returned sooner to the pool containing the small cover than the larger one. Additionally, after failing to catch fish in patches containing the highest prey density, the egrets subsequently preferred to return to such patches sooner. We show experimentally that previous failures influence the foraging decisions of a predator choosing how quickly to return to a previously visited patch.

Optimal foraging of little egrets and their prey in a foraging game in a patchy environment.

We explored the behavioral game between a predator, the little egret (Egretta garzetta), and a prey, the common goldfish (Carassius auratus), in a laboratory theater containing three fish pools. We tested the hypotheses that the egrets maximize their total capture success by responding to the fish's antipredatory behavior and that the behaviors of both players respond adaptively to the density distribution of fish among the pools. One experiment presented egrets with 15 fish per pool. The second experiment used a heterogeneous environment: pools 1, 2, and 3 had 10, 15, and 20 fish, respectively. Within each pool, fish could move between a safe, covered microhabitat and a risky, open microhabitat. Only the risky habitat had food, so fish were trading off food and safety by allocating the time spent in the two habitats. Egrets spent more total time in pools with more fish and returned to them sooner. Egrets maximized the number of fish they captured by following the matching rule of the ideal free distribution. The fish used the risky but productive habitat 65% of the time during experiments without egrets, but only 9% during experiments with 15 fish and egrets present somewhere in the theater. In addition, with egrets present, fish fine-tuned their behavior by reducing their use of the risky habitat as the egrets increased the frequency of their visits.

The ecology of cutaneous leishmaniasis in Nizzana, Israel: infection patterns in the reservoir host, and epidemiological implications.

We conducted an extensive interdisciplinary study in an emerging focus of cutaneous leishmaniasis in the Western Negev Desert of Israel between July 1998 and February 2000. The aims of the this study were to determine (1) the reservoir hosts, (2) the distribution of the pathogen within the host range, (3) the associations of host, vector, and pathogen within defined habitats, (4) the demographic distribution of the pathogen within the host populations, and (5) to apply the newly acquired epizootiological data to explain morbidity patterns in humans. Fourteen square (60 m width) sampling plots were delimited in three types of habitats each with a different kind of substrate: loess, sand, and sand-loess ecotone. Rodents and sand flies were trapped and several environmental variables were measured. Leishmania infections in rodents were detected microscopically in stained smears of ear tissue and by a Leishmania-specific polymerase chain reaction. Results indicate that, contrary to previous reports, Psammomys obesus and not Meriones crassus is the main reservoir host in the region. Additional rodents (12 Gerbillus dasyurus and two M. crassus) were also found positive for Leishmania DNA. Prevalence of Leishmania infections amongst P. obesus was highest in loess habitats (65%), intermediate in the sandy-loess ecotone (20%), and 0% in the sandy habitats. Psammomys obesus individuals in the loess habitat of the Nizzana ruins were larger, on average (probably older), than those in the sandy habitat of the Mt. Keren junction. Sand fly density was positively correlated to soil moisture being higher in the relatively humid plots of Nizzana ruins and much lower in the drier sandy soil of Mt. Keren. Elucidation of fundamental ecological factors affecting this disease has helped explain an apparent discrepancy between the distribution of the disease in the zoonotic system and among humans.

The effect of barn owls (Tyto alba) on the activity and microhabitat selection of Gerbillus allenbyi and G. pyramidum.

Predation plays an important role in ecological communities by affecting prey behavior such as foraging and by physical removal of individual prey. In regard to foraging, animals such as desert rodents often balance conflicting demands for food and safety. This has been studied in the field by indirectly manipulating predatory risk through the alteration of cues associated with increased risk such as cover or illumination. It has also been studied by directly manipulating the presence of predators in aviaries. Here, we report on experiments in which we directly manipulated actual predatory risk to desert rodents in the field. We conducted a series of experiments in the field using a trained barn owl (Tyto alba) to investigate how two species of coexisting gerbils (Gerbillus allenbyi and G. pyramidum) respond to various cues of predatory risk in their natural environment. The gerbils responded to risk of predation, in the form of owl flights and owl hunger calls, by reducing their activity in the risky plot relative to the control plot. The strongest response was to owl flights and the weakest to recorded hunger calls of owls. Furthermore, when risk of predation was relatively high, as in the case with barn owl flights, both gerbil species mostly limited their activity to the safer bush microhabitat. The response of the gerbils to risk of predation disappeared very quickly following removal of the treatment, and the gerbils returned to normal levels of activity within the same night. The gerbils did not respond to experimental cues (alarm clock), the presence of the investigators, the presence of a quiet owl, and recorded "white noise". Using trained barn owls, we were able to effectively manipulate actual risk of predation to gerbils in natural habitats and to quantify how gerbils alter their behavior in order to balance conflicting demands of food and safety. The method allows assessment of aspects of behavior, population interactions, and community characteristics involving predation in natural habitats.