Masters Thesis

An individual-based model for analyzing the evolution of traditional foraging strategies

An individual-based model has been developed to simulate the evolution of traditional foraging strategies in a fluctuating environment. The parameters and procedures are based on observed behavior of Barnacle geese, Branta leucopsis, during spring staging off the coast of Helgeland, Norway. Within a spatially heterogeneous environment, goose movement is modeled according to state dependent site selection decisions which maximize food intake. The aim of each individual is to optimize fitness (survival and reproduction) by gaining enough food (energy reserves) during three weeks of foraging to meet a threshold of energy necessary for successful reproduction. The geese return to the same islands each year, and on a daily basis choose unoccupied sites according to their rank in the population structured dominance hierarchy, memories of previously visited sites (tradition), past reproductive success, inherited genetic influence towards site faithfulness and/or site quality, and knowledge of the available biomass density. It is assumed that with each subsequent return to a specific location, increased familiarity of the area will benefit an individual through greater food acquisition by more efficient foraging practices. In the event of variable environmental conditions, geese are faced with a critical decision to return to previously visited sites or abandon tradition to explore for something better. It is shown that habitat quality plays an integral role in population dynamics. The evolution of foraging strategies which directly affects reproductive potential will inevitably determine the resilience of the population over time. Simulations of variable habitat availability were run and analyzed which serve to indicate the effect of certain strategies. It is shown that under environmental stasis the population stabilizes and traditional foraging is an optimal strategy. When faced with small perturbations to the foraging grounds, however, the population declines slightly but recovers quickly and generally maintains an affinity toward previously visited patches. Under significant environmental disturbance, site fidelity reduces the chance for reproductive success and survival, and does not usually remain a prevalent behavior in the population. Overall, tradition is most beneficial when reality and expectation coincide, otherwise a compromising strategy must be employed to mitigate the interim. This modeling approach has the potential to reveal significant insight into the emergence of stable responses to environmental disturbance.

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