15. Foraging behavior - Optimal Foraging Models What?...

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Optimal Foraging Models What? Where? How long? Nutrients?
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Optimality models (in general) predict which decisions an animal should make in order to maximize its inclusive fitness under a given set of conditions hypothesized to drive the behavior.
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Optimality models have 3 parts: DECISIONS. “Strategies” that are available to the animal. The animal performs 1 act out of all the possible actions available to it. CURRENCY. The criterion used to compare the value of different decisions. (Example: rate of energy intake, or time spent foraging.) CONSTRAINTS. Limitations on the animal. Can be internal (nutritional needs, ability to see only certain colors) or external (temperature, light levels).
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There are LOTS of different Optimal Foraging Models in the animal behavior literature describing basic Optimal Foraging Theory (OFT). We will examine 4 models that address the following questions: 1. What food items should the forager eat? 2. How long should a forager stay in a certain food patch? 3. How is foraging affected when certain specific nutrients are required? 4. How does variance in food supply affect decisions about what foods to eat?
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There are LOTS of different Optimal Foraging Models in the animal behavior literature describing basic Optimal Foraging Theory (OFT). We will examine 4 models that address the following questions: 1. What food items should the forager eat? 2. How long should a forager stay in a certain food patch? 3. How is foraging affected when certain specific nutrients are required? 4. How does variance in food supply affect decisions about what foods to eat?
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Simplest question: How do you choose between 2 food types? Examples: 2 prey types (carnivores) 2 species of seeds (granivores) 2 size classes of same food Each prey item (i) has: An energy value ( e i ) Encounter rate ( λ i ) Handling time ( h i )
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So for example: A prey type is encountered every 3 minutes (encounter rate). Once it is encountered it takes 2 minutes to kill and ingest (handling time). The forager receives 300 calories from the food (energy value). PROFITABILITY = Energy / Handling time. If we assume that the most profitable prey item will always be taken by the forager, then the question becomes: should any other type of prey be taken and when or under what conditions?
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This particular model assumes: 1. We can measure our prey types in some standard currency (such as calories). 2. Foragers cannot simultaneously handle one item and search for another. 3. Prey are recognized instantly and accurately. 4. Prey are encountered sequentially. 5. Foragers will always try to maximize their rate of energy intake. THE MAJOR CONCLUSION OF THIS MODEL IS: How often a predator encounters the less profitable item does NOT affect whether that item should be added to the diet or not. Rather, a critical encounter rate with the most profitable item is calculated. If that rate is high enough, ONLY prey item 1 will be taken, if not, then prey 1 AND 2 are taken.
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This note was uploaded on 05/02/2010 for the course BIO 359K taught by Professor Mcclelland during the Spring '08 term at University of Texas at Austin.

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15. Foraging behavior - Optimal Foraging Models What?...

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