06 覓食行為 ( Foraging behavior)

1. 動物行為學 (通識) 國立臺南大學 通識課程 2011年春 06 覓食行為 (Foragingbehavior) 鄭先祐 (Ayo)教授 國立台南大學 環境與生態學院 生態科學與技術學系 環境生態研究所 + 生態旅遊研究所 Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/

2. 覓食行為 (Foragingbehavior) • 螞蟻與真菌的關係 (Ant-fungus relationship) • 最佳覓食理論 (Optimal foraging theory) • What to eat • Where to eat • Specific nutrient constraints • Risk-sensitive foraging • 覓食與團體生活 (group life) • 天擇、親緣 與 seed caching • 學習與覓食

3. 1. 螞蟻與真菌的關係 (Ant-fungus relationship) • About 50 million years ago, ants began cultivating their own food by entering into a mutually beneficial relationship with certain species of fungi. • The ants promote the growth of the fungi, while also feasting on the vegetative shoots produced by their fungal partners. • Aside from humans, ants are one of the few groups on the planet that grow their own food.

4. A worker of the leaf-cutter ant tending a fungus garden. The thick whitish-gray coating of the worker is the mutualistic bacterium that produces the antibiotics that suppress the growth of parasite in the fungus garden.

5. Ant-fungus relationship • All twenty species of the fungus-growing ants examined had Streptomyces bacteria associated with them • Ants actually transmit the bacteria across generation, with parents passing the bacteria on to offspring. • Only females posses the bacteria. • The bacteria found on fungus-growing ants produce antibiotics that wipe out only certain parasitic diseases.

6. 2. 最佳覓食理論 (OFT) • What to eat? • Where to eat? • How long should a forager stay in a certain food patch? • Specific nutrient constraints • Risk-sensitive foraging • How does variance in food supply affect a forager’s decision about what food types to eat?

7. What to eat? • Cheetah (the forager) • foraging decision. • a female cheetah has killed a hare (the prey) • In making the decision whether to take hares rather than some other prey, the animal will compare the energy value, encounter rate, and handling time for each putative prey.

8. Optimal prey choice model • The model assumes: • Energy intake from prey can be measured in some standard currency • Foragers can’t simultaneously handle one prey item and search for another • Prey are recognized instantly and accurately • Prey are encountered sequentially • Natural selection favors foragers that maximize their rate of energy intake.

9. 案例：Great tit and Blue gill sunfish • optimal choice of diet • (A) great tits • (B) bluegill sunfish • The fit between expected and observed foraging is quite good, although the fish tended to oversample medium and small Dophnia in the high density treatment.

10. One classic early experiment using optimal foraging theory had mealworms of different sizes presented on a conveyor belt to great tits.

11. Great tits • Optimal foraging in great tits was examined in four density conditions.With a knowledge of exact encounter rates, handling times, and energy values, they were able to predict the birds’ optimal diet of large and small prey.

12. Bluegill sunfish The fit between expected and observed foraging is quite good, although the fish tended to oversample medium and small Dophnia in the high density treatment.

13. Where to eat • Marginal value theorem(邊際價值定律) • A forager should stay in a patch until the marginal rate of food intake– that is, the rate of food intake associated with the next prey item in its patch– is equal to that of the average rate of food intake across all patches available. • The greater the travel time between patches, the longer a forager should stay in a patch. • For patches that are already of generally poor equality when the forage enters the patch, individuals should stay longer in such patches than if they were foraging in an environment full of more profitable patches.

14. Patch choice For a bee, different flowers in a field of flowering plants might represent different patches

15. (A)To calculate the optimal time for a forager to remain in a patch, we begin by drawing a curve that represents the cumulative food gain in an average patch in the environment. Then, going west on the x-axis we find the average travel time between patches()

16. (B) We then draw a straight line from  that is tangent to the food gain curve. From the point of tangency, we drop a perpendicular dashed line to the x-axis, which gives us an optimal time (T) for the forager to stay in the patch.

17. Great tits: optimal time in patch and travel • (A) an artificial tree that allowed him to control both patch quality and travel time. • (B) the solid line is the predicted optimal time in a patch plotted against the travel time, which was calculated based on the marginal value theorem, while the data points are the observed times the birds stayed in the patch plotted as a function of travel time between patches. • The results clearly demonstrate that the amount of time birds spent in a patch matched the optimal time predicted by the marginal value theorem.

18. Great tits: optimal time in patch and travel (A) an artificial tree that allowed him to control both patch quality and travel time.

19. (B) the solid line is the predicted optimal time in a patch plotted against the travel time, which was calculated based on the marginal value theorem, while the data points are the observed times the birds stayed in the patch plotted as a function of travel time between patches. • The results clearly demonstrate that the amount of time birds spent in a patch matched the optimal time predicted by the marginal value theorem.

20. Specific nutrient constraints • 案例：Moose foraging on a salt budget. • Sodium is a particularly good candidate for a nutrient constraint study because vertebrates require large amounts of sodium, sodium is scarce, and besides water, sodium is the only nutrient for which a “specific hunger” has been documented in animals. • Moose need salt, and they acquire it from energy-poor plants. This takes time away from foraging on energy-rich terrestrial plants.

21. Moose foraging on a salt budget

22. Moose need salt, and the acquire it from energy-poor plants. This takes time away from foraging on energy-rich terrestrial plants.

23. Risk-sensitive foraging • Risk, the term was first used in economics, where more variance implied a greater chance of loss (or gain). • Increased variance in prey availability increases. • Rick-sensitive optimal foraging models • 案例：shrew • One key component to understanding risk-sensitive foraging is the hunger state of an animal.

24. Rick-sensitive optimal foraging models Imagine a shrew that must decide between a patch (1) that always yields 8 pellets once the cover is removed and a patch (2) in which half the time there are no pellets and half the time are 16 pellets. Both patches have the same mean (8), but the variance is greater in patch 2. If our forager takes variance into account, it is foraging in a risk-sensitive manner.

25. Forager, 3 different hunger states • Forager 1 has a hunger stat, in which it values every new food item equality. • Risk insensitive • Forager 2 is fairly satiated (相當飽足), and although every additional item it takes in has some value, each additional item is worth less and less. • Risk adverse • Forager 3 is starving, and every additional item it eats is worth more and more (to a limit). • Risk prone

26. A) hunger：Risk insensitive B) fairly satiated (相當飽足)： Risk adverse C) starving：Risk prone

27. Rule of thumb • As with all the mathematical models we analyze, we are not suggesting that animals make the mental calculations that we just went through, but rather that natural selection favors any “rule-of-thumb behavior. • The favored rule-of-thumb might be “when starving, use patches of food that have high variances.”

28. Junco foraging behavior has been used to test numerous optimal foraging models. utility functions and risk sensitivity

29. Risk adverse Risk prone (A) risk-prone juncos. The utility function for this junco indicates that each additional item the bird eats is worth more and more. (B) Risk adverse juncos. Each additional item a junco receives is worth less and less.

30. 3 覓食與團體生活 (Group Life) • Foraging in a group • Increasing the foraging group size increases the amount of food each forager receives. • 案例：Foraging in bluegills • Disentangling(解開) the effect of group size and cooperation on foraging success. • 案例： Wild dogs • Chimp (Tai chimp vs. Gombe chimp)

31. 案例： Foraging in bluegills • Group size and foraging success. • Meta-analysis on foraging success and group size in seven different species that hunt in groups. • Overall, a strong positive relationship between foraging success and group size.

32. 案例： Foraging in bluegills Bluegill sunfish (藍鰓魚)forage for small aquatic insects in dense vegetation. The bluegills’ foraging patterns approximate those predicted by theory.

33. In bluegill sunfish, the mean rate of prey captured increases with group size until group size reaches about four individuals.

34. Flushing effect, when bluegills forage in groups, they flush out more prey and attract other fish to the foraging site.

35. Disentangling(解開) the effect of group size and cooperation on foraging success • Individuals may cooperate with one another when hunting in groups. For example, wild dogs • Cooperative hunting in chimp populations, Tai chimps and Gombe chimps. • Tai chimps, cooperation hunting • Gombe chimps, no correlation between group size and hunting success. • The success rate for Gombe solo hunters was quite high compared with the individual success rate for Tai chimps.

37. Groups and public information • in public information models, individuals simply use the actions of others as a means of assessing the condition of the environment, and as such, public information allows group members to reduce environmental uncertainty. • Solitary foragers vs. foragers in a group. • Starlings(歐掠鳥) were tested using an array of food placed into cups.

38. Public information in starlings • A given bird (B1) fed from such a feeder either alone or paired with a second bird (B2) . • Prior to being paired with B1 partners, B2 birds had either been given the chance to sample a few cups in this feeder, or to sample all such cups. • Two results support the predictions of public information models. • When tested on completely empty feeding patches, B1 birds left such patches earlier when paired with any B2 bird than when foraging alone. • B1 birds left patches earliest of all when paired with B2 birds that had complete information about the patches.

40. Natural selection, and seed caching • Hippocampal (海馬體的) size and caching ability • To be associated with food retrieval. (food storage) • Foraging and brain size. • The volume of the hippocampal region relative to body mass was positively correlated with the extent of food storing in six species of birds,

41. Alpine cough • Jackdaw • Rook and crow combined • Red-billed blue magpie • Magpie • European jay

42. Chickadees (山雀) from Colorado or Alaska • Bring them back to laboratory at the University of California at Davis. • The results: • The birds from Alaska (food-scarce population) cached a greater percentage of seeds than the birds from Colorado (food-rich population). • The Alaska birds found more of their cached seeds than did the Colorado birds, and their searches were more efficient in that they made fewer errors

44. Phylogeny and caching ability • Evolutionary history of caching behavior in the corvid family (鴨科). • Phylogeny of 46 species • Non-cachers • Moderate cachers • Specialized cachers • Result: • The ancestral state of caching in corvids is “moderate caching”.

45. Learning and foraging • Foraging, learning, and brain size in birds • Hypothesized a neurobiological link between forebrain size and learning abilities in animals. • examples of foraging innovations in birds. • Data on 322 foraging innovations, including those in this list. • Relative forebrain size correlated with foraging innovation. Larger forebrains were more likely to have high incidences of foraging innovation • Learning and planning for the future • Social learning and foraging

49. Planning for the future • If animals could plan for the future based on prior experience, as we humans clearly do, there would be huge fitness benefits associated with such an ability. • Two requirements • The behavior must be novel, so that we can be certain that we are not seeding the manifestation of some innate action • The behavior in question must not be tied to the current motivational state of the animal, but rather to the anticipated motivational state at some point in the future.

50. 案例：Western scrub jays modify their foraging behavior in an attempt to plan for the future