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Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus

Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus. Pei-Jen Lee University of Virginia Portland, 2004. The Question: What drives omnivory in a trophic generalist species?. Coll and Guershon (2002):. nutrition balance / toxics dilution  obligate omnivores.

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Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus

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  1. Omnivory Driven by Pulse Resources in White-footed Mouse Peromyscus leucopus Pei-Jen Lee University of Virginia Portland, 2004

  2. The Question: What drives omnivory in a trophic generalist species? Coll and Guershon (2002): nutrition balance / toxics dilution  obligate omnivores food supplementation / competition avoidance  opportunistic omnivores Ostfeld and Keesing (2000) Dose pulse resources drive the behavioral switching between generalist and specialist strategy?

  3. Original Resource Distribution Resource Distribution after Specialized Consumption Background: Optimal Foraging Theory (Fretwell, 1972) Specialized Consumption Abundance /Consumption Generalized Consumption optimal Resource Quality Gradient

  4. The Study System: white-footed mouse in oak masting forests (Whitaker 1966; Wolff 1985)

  5. Tools and Assumptions I: Stable isotopes and carbon isotopic mixing xE (‰) = [(xE/ yE)sample / (xE/ yE)std – 1 ]*1000 13Cstd (‰): 15Nstd (‰): Pee Dee Belemnite Atmospheric N2 -- Carbon isotope mixing effect: i.e. C3 versus C4 plants -- Mixing equation: Δ 13Cmouse (‰) = fc4x (13Cc4 – 13Cc3) Assumptions: constant fractionation, equilibrium with food etc.

  6. mouse P 1-P Intermediate Consumers Producers Tools and Assumptions II : Trophic level based on nitrogen isotopes -- Nitrogen isotopic trophic effect: Let 15Ndiet-mouse = 2.7 ‰ 15Ndiet - intermediate consumer = 3 ‰ 15Nplant = a ‰ 15Nmouse = x ‰ Consumer trophic level: x-a Deviation from typical omnivory: |x-(a+3.9)|

  7. Experiment in 2003: simulation of seed mast event across two habitat types δ15N%o δ13C%o

  8. Result I:Fraction of diet derived from millet seeds Food addition effect: p=.01 Time effect: p<.0001 Food by Time: p=.01

  9. Result II:Intra-population divergence in trophic levels Start End p= .02

  10. Result III:Individual became specialized at millet seeds

  11. Summary Generalist consumers could trace the changes in food abundance efficiently at population level. Intra-population trophic divergence (CV of nitrogen isotopes) is greater in poor environment and smaller in rich environment. Deviation from omnivory and trophic level of individual consumers are directly related to the fraction of pulse resource in their diets. Pulse resources could drive the switching between generalist and specialist strategy in trophic generalist consumers.

  12. Acknowledgement Roulston, T’ai Wilbur, Henry Swap, Bob Carr, Dave / Morris, Clay Drummond, Brie / Sheu, Yu-Cheng ALL Blandy Farmers! Funding: Blandy Experimental Farm / Virginia Museum of Natural History

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