Pei-Jen Shaner University of Virginia

1. Omnivory and Population Dynamics of the White-footed Mouse Peromyscus leucopus in Response to Pulsed Food Resources Pei-Jen Shaner University of Virginia

2. Pulsed Food Resources 17 year cicadas Annual seeding and fruiting Annual insect emergence Predictability Acorn masting Climate-driven events Periodicity (year)

3. Omnivory Stablizing Arthropod Community (Fagan 1997)

4. Omnivores and Pulsed Food Resources

5. Nutrient Balance and Pulsed Food Resources Total Food Eaten Sawfiles + Alt. Food Low Palatability Alt. Food Present No. of Prey Eaten High Palatability Alt. Food Present No. of Sawfiles / Sq. Meters (Holling 1965)

6. Nutrient Balance and Pulsed Food Resources (Vickery et al. 1994)

7. Population Dynamics and Pulsed Food Resources (Elias et al. 2004)

8. Population Dynamics and Pulsed Food Resources (Marcello et al. 2008)

9. Dietary Shifts of the White-footed Mouse in Response to Pulsed Food Resources

10. Questions • Is the availability of foods with different nutritional values perceived by generalist consumer? • Does relative availability of foods with different nutritional values drive dietary shifts in a generalist consumer towards foods of complementary quality? From laboratory to field experimentation: Giving-up density + stable isotope

11. Marginal Value Theorem Giving-up density is based on marginal value theorem, as applied to animal optimal behaviors (Schoener 1971) Energy gain or lost per unit time Quitting harvest rate = Giving-up density dG/dtdL/dt Quitting harvest time Foraging time spent in a patch with a fixed amount of resource

12. Giving-up Density (GUD) The food density remaining in a patch with a fixed initial food density, after a period of optimal foraging by a forager(Brown 1988) GUD is based on marginal value theorem and is a surrogate to quitting harvest rate GUD is commonly used to measure: Perceived food availability Perceived predation risk

13. Measuring Food Availability with GUD Higher food availability Higher quitting harvest rate = Higher giving-up density Higher food availability Lower food availability *** * * *** * ** *** * * ** **** * ** ** * * *** ** * *** * * * ** * * ** * **** * * * * * ** * * * ** * * * * * * * * *

14. Measuring Food Availability with GUD Higher food availability Higher quitting harvest rate = Higher giving-up density Higher food availability Lower food availability *** * * *** * ** *** * * ** **** * ** ** * * *** ** * *** * * * ** * * ** * **** * * * * * ** * * * ** * * * * * * * * * ** ** GUD = 3 GUD = 1

15. Stable Nitrogen Isotopes Stable nitrogen isotopic compositions increase with trophic level:

16. Experimental Design Food addition in the summer of 2004: Millet seeds Mealworms Mixed seeds and worms Blandy Experimental Farm, VA

17. Nutritional Values of Millet Seeds and Mealworms Mealworm: higher protein gain, lower energy gain Millet seeds: higher energy gain, lower protein gain

18. Handling Time of Millet Seeds and Mealworms

19. Simulating Natural Pulsed Food Resources Millet seeds addition in similar density as acorn mast:

20. Measuring Giving-up Density

21. Giving-up Density of Millet Seeds and Mealworms

22. Consumption Rates of Millet Seeds and Mealworms Relative availability of mealworms increases Relative availability of millet seeds increases

23. Dietary Shifts in Response to Food Complementarity

24. Population Dynamics of the White-footed Mouse in Response to Pulsed Food Resources

25. Population Spatial Synchrony Spatial synchrony in population density or growth rate can be measured withcross-correlation coefficient Extrinsic factors such as large scale synchrony in weather conditions, food resource abundance, or predation can cause population spatial synchrony (Grenfell et al. 2004)

26. Demographic Processes Contributing to Synchrony

27. Demographic Processes Contributing to Synchrony

28. Experimental Design Three annual cycles: 2001-02, 2002-03, 2003-04 Sep-Oct of 2003-04, 200 pounds of millet seeds added per grid. • Population density(MNA) • Survivorship(MARK) • Reproduction(Percent breeding females) • Juvenile Recruitment(number of juveniles per adult female) Blandy Experimental Farm, VA

29. number of pairs between population i, j or cross-correlation coefficient between population i and j Measuring Population Synchrony Cross-correlation coefficient of population growth rates: growth rate for populationi, j over t time periods square root of the variance ingrowth ratefor population i, j

30. Stable Carbon Isotopes Stable carbon isotopic compositions vary between C3 plants (-35‰ to -23‰) and C4 plants (-23‰ to -6‰): (%C3 + %C4) = 1, fractionation =1.4‰ (MacAvoy et al. 2005)

31. Tracking Mouse Movement Fueled by Millet Seeds

32. Population Synchrony Induced by Millet Seeds

33. Survival Probability in Forest Populations b Survival Probability a

34. % Breeding Females in Forest Populations b % Breeding Females a

35. Juvenile Recruitment in Forest Populations No. Juveniles per Adult Female a b

36. Juvenile Movement Fueled by Millet Seeds

37. Conclusions • Dietary Shift Driven by Food Complementarity • Individual mouse responded to pulsed food resources of different nutritional values with dietary shifts towards complementary food types • Spatial Synchrony Driven by Pulsed Food Resources • Forest populations could potentially be synchronized by pulsed food resources • Demographic Processes Contributing to Synchrony • Female reproduction and juvenile dispersal fueled by pulsed food resources contributing to population synchronization

38. Future Research: Linking Individual Behavior to Population Dynamics and Ecosystem Processes • How does pulsed food resources drive dietary shifts and population dynamics of omnivores? Temporal (long-term and short-term) and spatial (local and landscape scale) patterns of pulsed food resources Nutrient constraints on dietary shifts in omnivores in response to pulsed food resources of complementary nutritional values Demographic processes in omnivores in response to temporal and spatial patterns of pulsed food resources

39. Future Research: Linking Individual Behavior to Population Dynamics and Ecosystem Processes • How do dietary shifts and population dynamics of omnivores affect food web processes? The effect of dietary shifts and population fluctuations in omnivores on alternative prey Degree of dietary shifts and patterns of population fluctuations among different omnivore species The strength of omnivory in a food web with multiple omnivore species

40. Future Research: Linking Individual Behavior to Population Dynamics and Ecosystem Processes • How do dietary shifts and population dynamics of omnivores affect ecosystem processes? Pulsed food resources v.s. pulsed nutrient input (macro- and micro-nutrient input) Degree of dietary shifts in omnivores driven by compensatory intake of macro- and/or micro-nutrients The stablizing role of omnivory in ecosystems facing increased disturbances

41. Future Research: A Blueprint Invertebrates ecologists Aquatic ecologists Ecosystem ecologists Statisticians Mathematicians Real ecosystems Model systems Field and lab experiments Isotope ecology Field observations Modeling and meta-analysis

42. THANK YOU!