Isotopic Tracing of Resource Movement by Animal Consumers Lee, P-J., S. A. Macko and M. A. Bowers University of Virginia TWS2004, Calgary, Canada

Background: Pulse resource in space and time Data: Virginia Department of Wildlife and Inland Fisheries -- acorn mast in Quercus spp.

Background: Isotopic tracing of resource movement  x E (‰) = [( x E/ y E)sample / ( x E/ y E)std – 1 ]*1000  13 C std (‰): PDB  15 N std (‰): Atmospheric N2 Stapp and Polis (2003) Marine resources penetrate inland areas through predator spillover effects and subsidize Peromyscus maniculatus populations

Methods: Mast simulation with C4 millet seeds millet seeds background plants Timing: September-October 2003 Intensity: 50 pounds of seed / 0.25 hectare / 10days Total amount: 200 pounds of seed / 0.25 hectare

Methods : Mice sampling and isotopic analysis capture-recapture trapping grids in forests and fields Isotopic analysis taking blood and hair samples

Methods : Quantifying resource taken by mice Mixing equation: Δ  x E (‰) = fb x ( x Eb) + (fm) x ( x Em) where (fb + fm) = 1 (MacAvoy et al. 2003) Isotopic turnover in mouse (Mus musculus) blood  13 C  15 N Half-life1720 Equilibrium7056

Methods : applying mouse turnover to P. leucopus Black bear (Ursus americanus) Mink (Mustela vison) Mouse Body mass of P. leucopus is similar to that of Mouse = 20grams

Result: Fraction in adult diets derived from millet seeds

Result: seed mast penetration into neighboring areas --no immigration from control grids to mast grids detected: mice commute to gain access to resources mast resources could penetrate ~140 meters into neighboring areas in forests

Result : Mice population density and reproduction output -- Equal number of juveniles per adult female between mast and control grids -- Juvenile mice incorporate equal amount of millet-derived nutrients towards hair tissue synthesis: 32%

Conclusions --Resource transport efficiency via consumer movements patchy resources could penetrate hundreds of meters --Mode of resource movement across neighboring food webs mice commute to mast grids at a scale of hundreds of meters --Reproductive output is equal between control and mast grids local patchy resources could promote regional population dynamics

Acknowledgement Stephen McAvoy Clay Morris Kimberly Spalding Blandy staff Funding: Blandy Experimental Farm Virginia Museum of Natural History The Wildlife Society student travel grant

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