UW Aquatic & Fishery Sciences Quantitative Seminar

Derek McClure

UW Quantitative Ecology and Resource Management and UW College of Forest Resources

Multiple food type producer/scrounger foraging models with an application to beach foraging northwestern crows, Corvus caurinus


Producer-scrounger (PS) game-theoretic models estimate the rate of kleptoparasitism among socially foraging organisms. To date PS models assume a single food type, however in many natural settings multiple food types are available. We extend the model of Vickery et al. (1991) to include any finite number of food types. We determine: 1) how encounter rates, finder's share, and energetic values of the food types effect the ESS proportion of producers and scroungers and 2) how changing the encounter rate of a single food type changes ESS proportions. We apply the model to a group of beach foraging northwestern crows to test model accuracy. We determine ESS is a function of an average of finder's shares weighted by encounter rates and energetic values. Change in ESS proportions due to change in encounter rates vary depending on the food type's relative finder's share and energetic value compared to the average respective quantities of the remaining food types. The model overestimates the observed scrounging rate of crows and makes qualitatively incorrect predictions on the change in scrounging behavior when encounter rates of particular food types are changed. We conclude this to result from both a lack of asymmetry among individuals and unrealistic assumptions from the model. We believe the model provides a platform for which asymmetries can be added for situations in which discovered food is shared among individuals and model assumptions are adequately met. However, if discovered food is not shared and assumptions are violated then a multiple food type stochastic model may be more appropriate.

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