Abstract
Understanding responses of organisms to spatial heterogeneity in resources has emerged as a fundamentally important challenge in contemporary ecology. We examined responses of foraging herbivores to multi-scale heterogeneity in plants. We asked the question, “Is the behavior observed at coarse scales in a patch hierarchy the collective outcome of fine scale behaviors or, alternatively, does the spatial context at coarse scales entrain fine scale behavior?” To address this question we created a nested, two-level patch hierarchy. We examined the effects of the spatial context surrounding a patch on the amount of time herbivores resided in the patch. We developed a set of competing models predicting residence time as a function of the mass of plants contained in a patch and the distance between patches and examined the strength of evidence in our observations for these models. Models that included patch mass and inter-patch distance as independent variables successfully predicted observed residence times (bears: r 2=0.67–0.76 and mule deer: r 2=0.33–0.55). Residence times of grizzly bears (Ursus arctos) and mule deer (Odocoileus hemionus) responded to the spatial context surrounding a patch. Evidence ratios of Akaike weights demonstrated that models containing effects of higher levels in the hierarchy on residence time at lower levels received up to 34 times more support in the data than models that failed to consider the higher level context for grizzly bears and up to 48 times more support for mule deer. We conclude that foraging by large herbivores is influenced by more than one level of heterogeneity in patch hierarchies and that simple empirical models offer a viable alternative to optimal foraging models for the prediction of patch residence times.
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Acknowledgements
This work was funded by National Science Foundation grants to Hobbs and Wunder (DEB 9981368) and to Shipley (DEB 9981242). We are grateful to the staff of the Colorado Division of Wildlife Foothills Research Facility at Fort Collins, CO, for help with the mule deer trials. We thank S. Albers, K. Bikowski, C. Bishop, S. Hobbs, W. Mulherin, L. Reynolds, and M. Rice for their invaluable assistance in animal care and field trials in Fort Collins. We appreciate the generosity of C.T. Robbins for allowing us to use the grizzly bears and facilities at the Bear Conservation and Research Center at Washington State University in Pullman, WA. T. Tollefson and M. Fisher helped conduct experiments with grizzly bears. We also thank Dr. M. McClure, Dr. B. Kotler, Dr. E.A. Laca and Dr. M. Åström for excellent reviews of this manuscript.
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Communicated by Craig Osenberg
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Searle, K.R., Vandervelde, T., Hobbs, N.T. et al. Spatial context influences patch residence time in foraging hierarchies. Oecologia 148, 710–719 (2006). https://doi.org/10.1007/s00442-005-0285-z
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DOI: https://doi.org/10.1007/s00442-005-0285-z