1. 06 覓食行為 (Foraging behavior)
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 (Foraging behavior)
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:
Ayo 2011 動物行為學 (通識)

2. 覓食行為 (Foraging behavior)
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
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

4. A worker of the leaf-cutter ant tending a fungus garden
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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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?
Ayo 2011 Ethology (通識)

7. What to eat? foraging decision. Cheetah (the forager)
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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

10. One classic early experiment using optimal foraging theory had mealworms of different sizes presented on a conveyor belt to great tits.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

14. Patch choice
For a bee, different flowers in a field of flowering plants might represent different patches
Ayo 2011 Ethology (通識)

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()
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

18. optimal time in patch and travel
Great tits:
optimal time in patch and travel
(A) an artificial tree that allowed him to control both patch quality and travel time.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

21. Moose foraging on a salt budget
Ayo 2011 Ethology (通識)

22. Moose need salt, and the acquire it from energy-poor plants
Moose need salt, and the acquire it from energy-poor plants. This takes time away from foraging on energy-rich terrestrial plants.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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
Ayo 2011 Ethology (通識)

26. A) hunger：Risk insensitive B) fairly satiated (相當飽足)： Risk adverse
C) starving：Risk prone
Ayo 2011 Ethology (通識)

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.”
Ayo 2011 Ethology (通識)

28. utility functions and risk sensitivity
Junco foraging behavior has been used to test numerous optimal foraging models.
utility functions and risk sensitivity
Ayo 2011 Ethology (通識)

29. Risk prone Risk adverse
(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.
Ayo 2011 Ethology (通識)

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)
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

33. In bluegill sunfish, the mean rate of prey captured increases with group size until group size reaches about four individuals.
Ayo 2011 Ethology (通識)

34. Flushing effect, when bluegills forage in groups, they flush out more prey and attract other fish to the foraging site.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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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.
Ayo 2011 Ethology (通識)

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.
Ayo 2011 Ethology (通識)

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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,
Ayo 2011 Ethology (通識)

41. Red-billed blue magpie
Alpine cough
Jackdaw
Rook and crow combined
Red-billed blue magpie
Magpie
European jay
Ayo 2011 Ethology (通識)

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
Ayo 2011 Ethology (通識)

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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”.
Ayo 2011 Ethology (通識)

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
Ayo 2011 Ethology (通識)

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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.
Ayo 2011 Ethology (通識)

50. 案例：Western scrub jays modify their foraging behavior in an attempt to plan for the future
Ayo 2011 Ethology (通識)

51. Western scrub jays and planning for the future
On alternate morning over the course of six days, birds were exposed to one of two compartments- one compartment contained food in the form of ground-up pine nuts, and the other compartment contained no food.
On the evening before each test, the birds were not fed any food, and they were therefore hungry during their exposure to test compartments.
After the six days of exposure to the two compartments, the birds were denied access to any food for two hours before dark, and then they were unexpectedly provided with a bowl of whole pine nuts – that is, food that could be cached.
Jays cached more nuts in the compartment in which they had consistently received no food in the past.
Ayo 2011 Ethology (通識)

52. Social learning and foraging in pigeons
Urban foragers.
Pigeons are scavengers, coming across novel food items all the time.
Such a species is ideal for study foraging and cultural transmission.
Ayo 2011 Ethology (通識)

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54. Pigeons in this experiment need to learn to pierce the red half of paper covering a box of seed. The graph shows average latency to eating for four groups: NM (no model) group, Bl (blind imitation) group, LE (local enhancement) group, and OL (observational learning) group.
Ayo 2011 Ethology (通識)

55. Producers and scroungers
Producers find and procure food
Scroungers make their living parasitizing the food that producers have uncovered.
Ayo 2011 Ethology (通識)

56. when a group member finally opens a tube with food in it, the food spills on the floor and is accessible to all. Out of sixteen pigeons, only two learned to open tubes, while fourteen acted as scroungers.
Ayo 2011 Ethology (通識)

57. Ayo NUTN website: http://myweb.nutn.edu.tw/~hycheng/
動物行為學 (通識)
問題與討論
國立臺南大學 通識課程 2011年春
Ayo NUTN website:
Ayo 2011 動物行為學 (通識)