Giving-up density and dietary shifts in the white-footed mouse, Peromyscus leucopus

Pei Jen Shaner*, Michael Bowers, Stephen Macko

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)


Dietary shifts are commonly exhibited by omnivorous consumers when foraging from variable food resources. One advantage of dietary shifts for a consumer is the ability to gain complementary resources from different foods. In addition, dietary shifts often affect food-web dynamics. Despite the importance of dietary shifts to organismal, community, and ecosystem ecology, empirical studies of the ecological mechanisms that control dietary shifts are limited in scope. In this study, we tested the effects of complementary resources on dietary shifts of an omnivorous mammal, the white-footed mouse Peromyscus leucopus, in the context of depletable food patches in the natural environment. We used two complementary resources: seeds that provide a higher energy gain per unit handling time and mealworms that provide a higher protein gain per unit handling time. Stable isotopes of carbon and nitrogen (δ13C, δ15N) in mouse plasma were used to quantify dietary shifts, and we determined giving-up density (GUD), the food density at which a forager leaves a food patch (for an optimal forager, it should correspond to the quitting harvest rate that balances net fitness gain with various costs of foraging). The results showed that GUD increased most significantly when a mixture of seeds and mealworms was added, compared to when only seeds or mealworms were added. This suggests that, given a similar level of food availability, a patch with a mixture of complementary foods is of higher quality than a patch with only one type of food. Moreover, GUD measured with seeds (GUDs) correlated positively with seed availability, and GUD measured with mealworms (GUDmw) correlated positively with mealworm availability, indicating that the marginal value of seeds or mealworms decreases with their relatively availability in the environment. As GUDs increased, P. leucopus shifted their diets toward higher trophic levels, and as GUDmw increased, P. leucopus shifted their diets toward lower trophic levels, suggesting dietary shifts driven by food complementarity. This study demonstrated that the combination of giving-up density and stable-isotope analysis holds great potential for testing ecological mechanisms underlying dietary shifts.

Original languageEnglish
Pages (from-to)87-95
Number of pages9
Issue number1
Publication statusPublished - 2007 Jan
Externally publishedYes


  • Complementary resources
  • Dietary shifts
  • Food availability
  • Food quality
  • Foraging behavior
  • Foraging theory
  • Giving-up density, GUD
  • Oak-hickory forest, Virginia, USA
  • Omnivory
  • Peromyscus leucopus
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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