Abstract
We used foraging trays to compare how oldfield mice, Peromyscus polionotus, altered foraging in response to the presence of fire ants, Solenopsis invicta, and in the presence of direct (predator urine) and indirect (sheltered or exposed microhabitat, moonlight, and precipitation) indicators of predation risk. Foraging reductions elicited by S. invicta were greater than reductions in response to well-documented indicators of risk (i.e., moonlit nights) and the presence of predator urine. The presence of S. invicta always led to reduced foraging, but the overall impact of S. invicta was dependent upon microhabitat and precipitation. When S. invicta was not present, foraging was greater in sheltered microhabitats compared to exposed microhabitats. S. invicta made sheltered microhabitats equivalent to more risky exposed microhabitats, and this effect was especially pronounced on nights without precipitation. The effect of S. invicta suggests that interactions with S. invicta may entail a potentially heavy cost or that presence of S. invicta may represent a more reliable indicator of imminent competition or predation compared to indirect cues of risk and predator urine. The presence of S. invicta led to reduced foraging under situations when foraging activity would otherwise be greatest (i.e., under vegetative cover), potentially reducing habitat quality for P. polionotus and the distribution of seeds consumed by rodents.
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Acknowledgements
We appreciate the outstanding field assistance of T. Hunt, D. Kuefler, E. Damschen, E. Koenig, and M. Burns. We are thankful to G. Curler for identifying ant specimens. Logistical support was provided by J. Blake, E. Olson, and other members of the U.S. Forest Service Savannah River. The manuscript benefitted from the comments of D. Coyle, E. Damschen, T. Hinkelman, W. Holtcamp, C. Kwit, and A. Wiewel. Funding and support were provided by the Department of Energy-Savannah River Operations office through the U. S. Forest Service Savannah River under Interagency Agreement DE-AI09-00SR22188. Funding also provided by NSF grant DEB-9907365, a Sigma Xi Grant in Aid of Research to J.L.O., an American Museum of Natural History Theodore Roosevelt Memorial Fund grant to J.L.O., a Professional Advancement Grant and EEB Fellowship to J.L.O. from Iowa State University, and an EPA Science to Achieve Results Fellowship to J.L.O. Ocelot urine was kindly supplied by J. Bush and Big Cat Rescue, Tampa, Fla.
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Orrock, J.L., Danielson, B.J. Rodents balancing a variety of risks: invasive fire ants and indirect and direct indicators of predation risk. Oecologia 140, 662–667 (2004). https://doi.org/10.1007/s00442-004-1613-4
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DOI: https://doi.org/10.1007/s00442-004-1613-4