103_20_full

103_20_full - PSYC 103 Winter 2011 Lecture 20 Feeding...

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Unformatted text preview: PSYC 103 Winter 2011 Lecture 20 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 delays. 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 prey density 1 2 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 better elsewhere. 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 between patches •  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” depletes •  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 memory. 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 time intervals. Ideal (optimal) behavior is always constrained by the psychology and biology of the organism. ...
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