干旱区生态环境知识资源中心

We used a behavioral bioassay, in the form of foraging behavior of Gerbillus allenbyi, 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 I-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 subplot. 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 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.