Converging on Predicted Equilibria

To test whether group-foraging spice finches would converge on the predicted equilibria, Mottley and Giraldeau modified their apparatus to allow movement between the producer and scrounger compartments. Their results show that subjects converged first on the predicted scrounger frequency in

Figure 10.6. Evidence in support of the assumption that foraging payoffs for scrounging are negatively frequency-dependent (i.e., payoff for the scrounger tactic declines with increases in the proportion of individuals in the group using that tactic). Mean (+ 1 SE) observed food intake rates are shown for producing and for scrounging in three captive flocks (A, B, and C) ofspice finches as a function ofthe number of individuals (out of six) scrounging. Subjects were tested undertwo patch conditions, covered and uncovered. In the covered patch condition, subjects experimentally constrained to use the scrounger tactic experienced reduced access to food. The purpose of these two patch conditions was to generate two distinct predictions for the equilibrium proportional use ofthe scrounger tactic. (After Mottley and Giraldeau 2000.)

Figure 10.6. Evidence in support of the assumption that foraging payoffs for scrounging are negatively frequency-dependent (i.e., payoff for the scrounger tactic declines with increases in the proportion of individuals in the group using that tactic). Mean (+ 1 SE) observed food intake rates are shown for producing and for scrounging in three captive flocks (A, B, and C) ofspice finches as a function ofthe number of individuals (out of six) scrounging. Subjects were tested undertwo patch conditions, covered and uncovered. In the covered patch condition, subjects experimentally constrained to use the scrounger tactic experienced reduced access to food. The purpose of these two patch conditions was to generate two distinct predictions for the equilibrium proportional use ofthe scrounger tactic. (After Mottley and Giraldeau 2000.)

the covered-patch condition and then on the higher predicted scrounger frequency in the uncovered-patch condition. These results constitute the best evidence to date that social foragers can adjust their scrounging frequency to predicted levels.

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