Evol Ecol Res 4: 495-518 (2002)     Full PDF if your library subscribes.

Foraging games between gerbils and their predators: temporal dynamics of resource depletion and apprehension in gerbils

Burt P. Kotler,1,2* Joel S. Brown,2 Sasha R.X. Dall,1 Shaan Gresser,1 David Ganey1 and Amos Bouskila1,3

1Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, Israel, 2Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, USA and 3Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel

Address all correspondence to Burt P. Kotler, Blaustein Institute for Desert Research, Mitrani Department for Desert Ecology, Ben-Gurion University of the Negev, Midreshet Sede Boker 84990, Israel.
e-mail: kotler@bgumail.bgu.ac.il


Predator–prey interactions constitute a foraging game when prey individuals manage risk from predators and predator individuals manage fear in their prey. As tools for managing risk, clever prey can use time allocation and apprehension (redirecting attention from foraging to predator detection). One such foraging game occurs between gerbils and their predators on the sand dunes of the Negev Desert. Here, interacting species of gerbils compete for patches of seeds that renew daily by afternoon winds. In such circumstances, gerbils are expected to deplete resource patches over the course of the night, the predators are expected to hunt when gerbil activity is highest, and gerbils are expected to be most apprehensive when predators are most active and most deadly. We tested these predictions for gerbils in two field experiments using seed trays to measure resource depletion, gerbil activity and apprehension over the course of the night, between the bush and open microhabitats and at four moon phases (new, half waxing, full and half waning). Gerbils depleted seed resources more quickly in the bush microhabitat than the open and more quickly at new moon than at other moon phases. Gerbil activity at new moon was high throughout most of the night, but decreased towards dawn. In contrast, activity at full moon was generally low, but increased towards dawn. The two gerbil species Gerbillus andersoni allenbyi and G. pyramidum partitioned the night, with G. pyramidum visiting resource patches earlier in the night and encountering a richer, but more risky environment, and G. a. allenbyi foraging later in an environment characterized by fewer seed resources, but lower risk. The same pattern extended over moon phases, with G. pyramidum foraging relatively more at full and waning half moon. Apprehension by gerbils was higher early in the night than later and higher at full moon than new moon. Schedules of apprehension changed according to moon phase and may have differed between the two gerbils. Finally, apprehension was higher in the open microhabitat, although the opposite was true at the beginning of the night. This foraging game affects three trophic levels, including the effect of the gerbils on the availability and distribution of seeds, the competitive interaction between the two gerbil species and the predator–prey interaction between gerbils and owls.

Keywords: apprehension, ecology of fear, foraging behaviour, foraging games, game theory, gerbils, giving-up density, optimal patch use, owls, predator–prey interactions, resource depletion, risk of predation, temporal partitioning, vigilance.

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