Optimal Foraging Optimal Foraging BehaviorBehavior

Species should forage in an efficient manner that maximizes benefits and minimizes costs

Varies with species and environmental context

MacAuthur and Pianka – optimal foraging theory

Optimal Foraging Optimal Foraging TheoryTheory

Studied how long a predator will forage in a specific area Influence of prey density on the length of time a

predator will forage in an area Influence of prey variety on a predator’s choice of

acquired prey

Main assumption: natural selection has operated strongly on foraging behavior, then foraging behavior should be adaptive.

Used to generate models and predictions about foraging behavior

Optimal foraging Optimal foraging modelsmodels

Attempt to predict the behavior of an animal while it searches for food, a nesting site, or other key niche components.

Outcome of models predicts how individuals move in the environment and how individuals are distributed in the environment.

Real behavior vs. Real behavior vs. modelsmodels

When real foraging behavior differs from optimal behaviors it gives us clues to constraints either in the animals’ behavior or thinking or in the environment

Once constraints are identified, behavior does approach optimal foraging pattern

Marginal Value Marginal Value TheoremTheorem

“giving up time”

As an animal forages, the amount of energy gain gradually begins to slow down as food becomes scarcer in the patch

Travel time governs decision

Ideal Free DistributionIdeal Free Distribution

Patch quality and competition taken into account

Animals will distribute themselves in the place where gains will be the highest

At equilibrium, the number of competitors in each patch is proportional to the quality of the patch

Different versions of Different versions of OFTOFT

Optimal diet model

Patch selection theory

Central place foraging theory

Optimal Diet modelOptimal Diet model

E/h where E = energy content of each item in the diet h = handling time

(energy) required to capture, subdue, and consume each item

Ei/hi

Where Ei = energy (caloric) content of a new diet item and hi = handling time (or energy) required to capture, subdue and consume new prey item

Is new diet more favorable than the old diet?

Search time (More energy) E/(s + h) where s=average search time for old diet

Diet should expand if Ei/hi > E/(s + h)

Central Place Foraging Central Place Foraging TheoryTheory

Special case of the marginal value theorem

Deals with animals that forage around a retreat site

Deals with how much an animal will gather before returning to retreat

Also with how best to exploit the resources around the retreat before moving on

Zach’s study of Zach’s study of Northwestern CrowsNorthwestern Crows

Crows drop shellfish to break outer shell

Experimenter dropped shells from different heights

Determined the optimal height necessary to break shells

Crows dropped shells at similar height

SunfishSunfish

Provided sunfish with prey of different sizes and densities

Fish took most energetically rich prey under the appropriate conditions