Patch use under predation hazard: Effect of the red imported fire ant on deer mouse foraging behavior
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We examined patch use of deer mice foraging in the presence vs. the absence of red imported fire ants in a laboratory experiment. We tested the H = P + C + MOC patch use model (H, harvest rate; P, predation risk; C, metabolic costs; MOC, missed opportunity costs), an extension of the marginal-value theorem, by comparing in-patch harvest rates and giving-up densities (GUDs) in the presence and the absence of fire ants. The model predicts that foragers should seek patches that yield higher feeding rates in the presence of increased costs. GUDs also should increase, since they should correlate directly with quitting-harvest rates, as long as the forager experiences diminishing returns on its rate of resource harvest. We identified behavioral trade-offs made by deer mice when foraging in the presence of fire ants. In the presence of fire ants, mice harvested a greater proportion of seeds from, spent more time in, and made more visits to rich patches than to poor, whereas in the absence of fire ants, these variables did not differ between rich and poor patches. Mice also increased their in-patch harvest rate in the presence of fire ants, as predicted by the H = P + C + MOC model, but harvested patches to a lower GUD. Mice left patches at lower final seed densities, but were able to maintain a higher mean in-patch harvest rate, suggesting that mice foraged more efficiently in the presence of fire ants. When fire ants were present, deer mice spent more time on out-of-patch handling (fire ants were confined to patches). Despite increased costs or lost time due to taking seeds away from the ants for consumption, mice were able to harvest the same number of seeds in the same total time, at the same mean harvest rate. By biasing effort toward more energetically profitable rich patches and by increasing their in-patch harvest rate, deer mice were able to obtain the same net yield in the same time, despite increased costs.
author list (cited authors)
Holtcamp, W. N., Grant, W. E., & Vinson, S. B.
complete list of authors
Holtcamp, WN||Grant, WE||Vinson, SB