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Expansion or extinction? The effects of environmental stochasticity on population growth rate in yellow baboons (Papio cynocephalus).
PULLIAM, JULIET*,1,2, ALBERTS, SUSAN1, ALTMANN, JEANNE2, 1 Duke University, Durham, NC2 Princeton University, Princeton, NJ
ABSTRACT- The effects of environmental and demographic stochasticity on population growth rate were examined for a wild baboon population. We incorporated deterministic matrix projection models into a series of stochastic simulations. The deterministic model predicted a yearly population growth rate of =1.0389. A model incorporating only demographic stochasticity predicted slightly lower lambdas of 1.0177 to 1.0270; however, a stochastic model incorporating both environmental and demographic stochasticity predicted stochastic lambdas between 0.9727 and 1.0264, with the lowest lambdas corresponding to finer-grained partitioning of the data and therefore relatively high resolution of environmental change. Although demographic stochasticity seems to have little effect on long-term population dynamics, environmental variation does matter. In particular, the model suggests that the Amboseli baboon population may be vulnerable to extinction in the face of environmental variability, even though the mean population growth rate is positive. We gratefully acknowledge financial support from the National Science Foundation, the Chicago Zoological Society, and the Arnold and Mabel Beckman Foundation.
KEY WORDS: environmental stochasticity, population growth, Papio cynocephalus, matrix models