The costs of apprehensive foraging

Zvika Abramsky, Michael L. Rosenzweig, Aziz Subach

Research output: Contribution to journalArticlepeer-review

77 Scopus citations


We used a behavioral bioassay, in the form of foraging behavior of Gerbillus altenbyi, and the ideal free distribution to estimate the costs associated with risk of predation. Experiments were conducted in two pairs of 2-ha field enclosures. Risk of predation was introduced to one 1-ha subplot of each pair of enclosures either by simulating the light of a full moon or by causing trained owls to fly over our experimental subplots. We used a titration method to estimate the energetic costs associated with risk of predation. We added seeds to the 1-ha subplot of each enclosure that experienced the risk of predation. The adjacent subplot served as a control. Without seed addition the subplot without risk of predation had more foraging activity: the foragers were avoiding the risk of predation. As the amount of seeds in the treatment increased, the gerbils responded smoothly and quantitatively and shifted their foraging activity back to the subplot with the seeds (and risk). At addition rates of 4.24-8.47 g seeds per individual per ha per night (simulated-moonlight treatment) and 4.24-5.64 g seeds per individual per ha per night (owl-flights treatment) the seed addition compensated for the extra risk. At these rates the foraging activity on the two subplots of each enclosure was the same. Our results suggested that, when challenged by the threat of predation, G. allenbyi individuals spent at least 25% of their foraging time being vigilant.

Original languageEnglish (US)
Pages (from-to)1330-1340
Number of pages11
Issue number5
StatePublished - May 1 2002


  • Apprehension
  • Behavioral bioassay
  • Energetic costs
  • Gerbillus allenbyi
  • Gerbils
  • Ideal free distribution
  • Predation risk
  • Titration

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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