06 ???? (Foraging behavior)

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06 ???? (Foraging behavior)
????? (??)
?????? ???? 2011??

• ??? (Ayo) ??
• ?????? ???????
• ?????????
• ??????? ???????

Ayo NUTN Web http//myweb.nutn.edu.tw/hycheng/
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???? (Foraging behavior)

• ???????? (Ant-fungus relationship)
• ?????? (Optimal foraging theory)
• What to eat
• Where to eat
• Specific nutrient constraints
• Risk-sensitive foraging
• ??????? (group life)
• ????? ? seed caching
• ?????

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1. ???????? (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.

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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.
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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.

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2. ?????? (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
  foragers decision about what food types to eat?

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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.

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Optimal prey choice model

• The model assumes
• Energy intake from prey can be measured in some
  standard currency
• Foragers cant 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.

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??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.

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

1. 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.

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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.
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Where to eat

• Marginal value theorem(??????)
• 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.

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

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

• ??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.

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Moose foraging on a salt budget
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Moose need salt, and the acquire it from
energy-poor plants. This takes time away from
foraging on energy-rich terrestrial plants.
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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
• ??shrew
• One key component to understanding risk-sensitive
  foraging is the hunger state of an animal.

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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.
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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 (????), 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

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A) hungerRisk insensitive B) fairly satiated
(????) Risk adverse C) starvingRisk prone
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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.

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Junco foraging behavior has been used to test
numerous optimal foraging models. utility
functions and risk sensitivity
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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.
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3 ??????? (Group Life)

• Foraging in a group
• Increasing the foraging group size increases the
  amount of food each forager receives.
• ??Foraging in bluegills
• Disentangling(??) the effect of group size and
  cooperation on foraging success.
• ?? Wild dogs
• Chimp (Tai chimp vs. Gombe chimp)

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?? 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.

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?? Foraging in bluegills
Bluegill sunfish (???) forage for small aquatic
insects in dense vegetation. The bluegills
foraging patterns approximate those predicted by
theory.
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In bluegill sunfish, the mean rate of prey
captured increases with group size until group
size reaches about four individuals.
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Flushing effect, when bluegills forage in groups,
they flush out more prey and attract other fish
to the foraging site.
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Disentangling(??) 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.

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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 (???) were tested using an array of
  food placed into cups.

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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.

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Natural selection, and seed caching

• Hippocampal (????) 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,

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1. Alpine cough
2. Jackdaw
3. Rook and crow combined
4. Red-billed blue magpie
5. Magpie
6. European jay

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Chickadees (??) 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

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Phylogeny and caching ability

• Evolutionary history of caching behavior in the
  corvid family (??).
• Phylogeny of 46 species
• Non-cachers
• Moderate cachers
• Specialized cachers
• Result
• The ancestral state of caching in corvids is
  moderate caching.

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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

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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.

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

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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.

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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.
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Producers and scroungers

• Producers find and procure food
• Scroungers make their living parasitizing the
  food that producers have uncovered.

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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.
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????? (??)
?????
?????? ???? 2011??

• Ayo NUTN website
• http//myweb.nutn.edu.tw/hycheng/