Abstract
Realistic functional responses are required for accurate model predictions at the community level. However, controversy remains regarding which types of dependencies need to be included in functional response models. Several studies have shown an effect of very high predator densities on per capita predation rates, but it is unclear whether this predator dependence is also important at low predator densities. We fit integrated functional response models to predation data from 4-h experiments where we had varied both predator and prey densities. Using an information theoretic approach we show that the best-fit model includes moderate predator dependence, which was equally strong even at low predator densities. The best fits of Beddington–DeAngelis and Arditi–Akçakaya functional responses were closely followed by the fit of the Arditi–Ginzburg model. A Holling type III functional response did not describe the data well. In addition, independent behavioral observations revealed high encounter rates between predators. We quantified the number of encounters between predators and the time the focal predator spent interacting with other individuals per encounter. This time “wasted” on conspecifics reduced the total time available for foraging and may therefore account for lower predation rates at higher predator densities. Our findings imply that ecological theory needs to take realistic levels of predator dependence into account.
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Acknowledgments
We thank E. Hammill, A. Narwani, and S. Pavey for valuable comments on previous drafts of this manuscript and E. von Aderkas for technical assistance with behavioral observations. This research was funded by the Canada Research Chairs Program and an NSERC of Canada Discovery grant to B. R. A. This research conforms to all applicable regulatory requirements.
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Communicated by Libby Marschall.
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Kratina, P., Vos, M., Bateman, A. et al. Functional responses modified by predator density. Oecologia 159, 425–433 (2009). https://doi.org/10.1007/s00442-008-1225-5
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DOI: https://doi.org/10.1007/s00442-008-1225-5