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...

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

動物行為學 ( 通識 ) 國立臺南大學通識課程 2011 年春

Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/

Ayo 2011 動物行為學 ( 通識 )

1

覓食行為 (Foraging behavior)

Ayo 2011 Ethology ( 通識 )2

1. 螞蟻與真菌的關係 (Ant-fungus relationship)2. 最佳覓食理論 (Optimal foraging theory)

What to eatWhere to eatSpecific nutrient constraintsRisk-sensitive foraging

3. 覓食與團體生活 (group life)4. 天擇、親緣與 seed caching5. 學習與覓食

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.


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.

Ant-fungus relationship


1. All twenty species of the fungus-growing ants examined had Streptomyces bacteria associated with them

2. Ants actually transmit the bacteria across generation, with parents passing the bacteria on to offspring.

3. Only females posses the bacteria.4. The bacteria found on fungus-growing

ants produce antibiotics that wipe out only certain parasitic diseases.

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?

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.

Optimal prey choice model


The model assumes:1. Energy intake from prey can be

measured in some standard currency 2. Foragers can’t simultaneously handle

one prey item and search for another3. Prey are recognized instantly and

accurately4. Prey are encountered sequentially5. Natural selection favors foragers that

maximize their rate of energy intake.

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.


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


Great tits

(A)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.


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.

Where to eat


Marginal value theorem( 邊際價值定律 )1. 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.

2. The greater the travel time between patches, the longer a forager should stay in a patch.

3. 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.


Patch choice

For a bee, different flowers in a field of flowering plants might represent different patches


(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()


(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.

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.


(A) an artificial tree that allowed him to control both patch quality and travel time.

Great tits: optimal time in patch and travel


(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.

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.


Moose foraging on a salt budget


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

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.


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.

Rick-sensitive optimal foraging models

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


A) hunger ： Risk insensitiveB) fairly satiated ( 相當飽足 ) ： Risk adverse C) starving ： Risk prone

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.”


Junco foraging behavior has been used to test numerous optimal foraging models.

utility functions and risk sensitivity


Risk adverseRisk 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.

3 覓食與團體生活 (Group Life)


Foraging in a groupIncreasing 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 dogsChimp (Tai chimp vs. Gombe chimp)

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.


Bluegill sunfish ( 藍鰓魚 ) forage for small aquatic insects in dense vegetation.

The bluegills’ foraging patterns approximate those predicted by theory.

案例： Foraging in bluegills


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


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

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 huntingGombe 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.

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.

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.

Natural selection, and seed caching


Hippocampal ( 海馬體的 ) size and caching abilityTo 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,


A. Alpine cough

B. Jackdaw

C.Rook and crow combined

D.Red-billed blue magpie

E. Magpie

F. European jay

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

Phylogeny and caching ability


Evolutionary history of caching behavior in the corvid family ( 鴨科 ).

Phylogeny of 46 speciesNon-cachersModerate cachersSpecialized cachers

Result:The ancestral state of caching

in corvids is “moderate caching”.

Learning and foraging


Foraging, learning, and brain size in birdsHypothesized 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 futureSocial learning and foraging

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.


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

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.

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.


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.

Producers and scroungers


Producers find and procure foodScroungers make their living

parasitizing the food that producers have uncovered.


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 NUTN website:http://myweb.nutn.edu.tw/~hycheng/

問題與討論

Ayo 2011 動物行為學 ( 通識 )

57

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...

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Transcript of 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...

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...

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Transcript of 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...

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...

Transcript of 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...