Bio 281 2011 lecture 10 - Foraging - lecture notes large.pdf
- 1. Foraging
- 2. Cost/benefit analysis to generate predictions regarding behavior Optimal foraging theory (OFT) What should an animal eat? Where should an animal eat?
- 3. Cost/benefit analysis to generate predictions regarding behavior Optimal foraging theory (OFT) Foragers cannot handle >1 prey at once Prey are recognized instantly Prey are encountered sequentially Foragers maximize rate of energy intake
- 4. Optimal foraging theory (OFT) E/T for prey type 1 = Ts λ1 e1 Ts + Ts λ1 h1 Maximize energy per unit time (E/T) T = total time Ts = search time λ = encounter rate h = handling time Total prey type 1 captured Total search time Handling time given search
- 5. Optimal foraging theory (OFT) E/T for prey type 1 = λ1 e1 1 + λ1 h1 Maximize energy per unit time (E/T) T = total time Ts = search time λ = encounter rate h = handling time
- 6. A bird in the hand… Imagine two prey types, 1 and 2 e2/h2 < e1/h1 What should an animal do if it encounters prey 1? Eat it! What should an animal do if it encounters prey 2? It depends…
- 7. A bird in the hand… What should an animal do if it encounters prey 2? It depends… Predictions 1. If true, eat only prey 1 (specialize) 2. If not true, take both prey 1+2 (generalize) λ1e1 1 + λ1h1 > λ1e1 + λ2e2 1 + λ1h1 + λ2h2
- 8. Predictions 3. Decision to specialize is based on encounter rate of prey 1 4. Threshold level λ1 > e2 e1h2 – e2h1 A bird in the hand…
- 9. Sir John Krebs Empirical evidence for prey models great tit
- 10. Empirical evidence for prey models Bluegill predator Daphnia prey (left) Prey size class (I = largest) Prey actually consumed Prey predicted based on availability Low prey density High prey density High prey density
- 11. Meadow vole Short-tailed shrew House mouse White-footed mouse Others Meadow vole Short-tailed shrew House mouse White-footed mouse Others Prey eaten Prey available Prey consumed according to profitability, not simply encounter rate Prey models
- 12. Prey easy to find, hard to catch: should specialize Prey hard to find, easy to catch: should generalize Prey models Some general predictions:
- 13. Foragers cannot handle >1 prey at once Prey are recognized instantly Prey are encountered sequentially Foragers maximize rate of energy intake Prey models How to minimize search time?
- 14. Search image = cognitive representation of prey type Search images Aid in avoidance of noxious prey
- 15. Increasing prey profitability How to maximize e/h? Decrease h! 22 appendages 25,000 Eimer’s organs 100,000 neurons (6x that of human hand) star-nosed mole
- 16. How to reduce handling time
- 17. How to reduce handling time cortical magnification: area of somatosensory cortex per sensory organ
- 18. Less than ¼ of a second to identify and handle prey Moles like fast food
- 19. Ken Catania Moles like fast food
- 20. What should a mole do if it encounters prey 2? Eat it! λ1e1 1 + λ1h1 > λ1e1 + λ2e2 1 + λ1h1 + λ2h2 Predictions 1. If true, eat only prey 1 (specialize) 2. If not true, take both prey 1+2 (generalize) Handling times for small prey are negligible The optimal mole
- 21. Where to forage? Prey found in patches Patches distributed in habitat
- 22. Patch time Energy gain Patch models How long should an animal stay in a patch? Depends on the distance between patches
- 23. Patch time Energy gain Travel time to next patch long short optimal patch times Patch models: marginal value theorem
- 24. Empirical evidence: marginal value theorem Mantid predator House fly prey
- 25. Empirical evidence: marginal value theorem great tit
- 26. Central place foragers violate patch laws Exceptions to OFT Collect loads before returning to central place chipmunk
- 27. parasitoid wasp Sub-optimal foraging in Atta ants? Constraints limit optimal foraging Exceptions to OFT