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Unformatted text preview: PSYC 103
Feeding & Foraging Foraging: outline 1. What to do in a simple environment of unchanging patches 2. What to do if those patches change 3. Where to forage when in a group 4. What to forage on Fluctuating patches Sampling behavior tracks changes in the environment (patch
abundance) When the fluctuating patch is
good, pigeons tend to choose
it until it goes bad again
When the fluctuating patch is
bad, pigeons tend to choose
the stable patch more often Sampling frequency is inversely proportional to reinforcement probability in the constant patch Foraging models
• Maximize reinforcement?: do animals choose the option the has the highest probability of payoff at a given point in time -- no.
• Scalar expectancy theory (SET): choice between reward probabilities is a
choice between delays to to food. Different delays (intervals) are
remembered, and the animal samples from the distribution of remembered
FI4 VI4 Concurrent FI4 VI4
Equal payoffs More short intervals will
come from this memory Maximizes rate under psychological constraints Choosing patches in a group
? 1 10 Ideal free distribution: The distribution in which each individual can maximize its
intake under ideal conditions (perfect information, equal competitiveness); a perfect
“match” Under-match Individual learning The proportion of individuals at a patch quickly comes to match the
Initial match to rates of throwing Subsequent match
to size of bread Note: the distribution of ducks stabilizes before individuals
have a chance to visit more than one patch What happens when patches deplete?
Successive prey items take longer and longer to find: When do you
give up and leave?
Marginal value theorem (MVT): Forager should stay at the patch until the rate of energy intake falls below the average in the habitat. After this point, it could do
MVT implies that animals track rate of intake and overall quality of environment 2. Giving up time was longer in
the poor environment
(consistent with MVT) Giving up time 1. Giving up time is constant
within each environment,
regardless of patch quality Remembering and Averaging time
MVT implies accurate representation of time in the patch and travel time
• Train starlings to feed from a recognizable location
• Vary patch depletion (rate of dispensing) and location of feeding station Behavior follows prediction from MVT:
the longer the round trip, the more
meal worms collected Remembering and Averaging time
• When pecking, variable numbers of prey are dispensed at fixed intervals, until “patch”
• Starling must fly between perches several times to reset patch (i.e. fly to new ‘patch’) Pecking rates peak at the value of the inter-prey interval (and scale with magnitude)
as for peak procedure
What about giving up time? Giving up scales with inter-prey interval too! Longer inter-prey interval lead to slower
giving-up (following Weber’s law). Prey selection Cycle of events
Handling requires time…time
not spent feeding Task: find items that maximize energy per unit of handling time (E/H)
When times are good (lots high E/H items): be choosy
When times are bad: take what you can get.
In general, prey selection follows other models of choice (e.g. SET, delay
reduction hypothesis) in minimizing the delay to food Concepts
1. 2. 3.
4. 5. Evolution can produce simple rules for doing complex
things, that do not require theoretical computations or
explicit representations of variables
Most environments vary across time and space.
Optimal decision making may require information about
the whole environment drawn from samples and
The time available for foraging is usually limited, best
strategies may change as time runs out.
Information about time intervals is vital. Some animals
use threshold change, others represent and remember
Ideal (optimal) behavior is always constrained by the
psychology and biology of the organism. ...
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- Spring '07