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Oecologia

, Volume 168, Issue 3, pp 659–670 | Cite as

Scale-dependent neighborhood effects: shared doom and associational refuge

  • Sara E. EmersonEmail author
  • Joel S. Brown
  • Christopher J. Whelan
  • Kenneth A. Schmidt
Behavioral ecology - Original Paper

Abstract

A resource’s susceptibility to predation may be influenced by its own palatability and the palatability of its neighbors. We tested for effects of plant chemical defenses on seed survival by manipulating the frequency of palatable and less palatable sunflower seeds in food patches subject to harvest by fox squirrels (Sciurus niger) and gray squirrels (Sciurus carolinensis). We varied resource distributions at three scales: among stations (aggregates of patches ca. 50 m apart), among patches immediately adjacent to each other, and within patches. When food patches were segregated into high-palatability and low-palatability stations (Experiment 1), seeds suffered greater mortality at stations with high levels of palatable seeds. In the same experiment, within patches, squirrels selected strongly for palatable seeds over less palatable seeds. When high- and low-palatability food patches were placed together at the same stations (Experiment 2), increasing densities of co-occurring palatable seeds amplified the mortality of less palatable seeds, indicating “shared doom.” When palatable and less palatable seeds were partitioned into micropatches (Experiment 3), associational effects disappeared, as predicted. Furthermore, selectivity in less palatable patches increased as the initial densities of palatable seeds increased, and selectivity in palatable patches decreased as the initial densities of less palatable seeds increased. Foraging theory predicts associational effects among prey that vary in palatability. Our results show how the type and magnitude of associational effects emerge from the interplay among the spatial scale of prey heterogeneity, the diet selection strategy, and the scale-dependent foraging responses of the consumer.

Keywords

Plant defenses Micropatch partitioning Shared doom Associational refuge Squirrels Giving-up densities 

Notes

Acknowledgments

We thank the staff of the Morton Arboretum for accommodating this research, H.F. Howe for his advice and assistance, M.A. Abu Baker, D.W. Morris, and three anonymous reviewers for advice on the manuscript, and J. Lam, B. Zapanta, and S. Shah for their field and lab assistance.

Supplementary material

442_2011_2144_MOESM1_ESM.pdf (65 kb)
Supplementary material 1 (PDF 64 kb)

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Sara E. Emerson
    • 1
    Email author
  • Joel S. Brown
    • 1
  • Christopher J. Whelan
    • 2
  • Kenneth A. Schmidt
    • 3
  1. 1.Biology DepartmentLawrence UniversityAppletonUSA
  2. 2.Illinois Natural History Survey, c/o Department of Biological SciencesUniversity of Illinois at ChicagoChicagoUSA
  3. 3.Department of Biological SciencesTexas Tech UniversityLubbockUSA

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