PARENT SESSION
Oral Session # 16: Ecological Modeling I.
Presiding: C Ray
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 102.

Sensitivity of density dependent populations to environmental variability.

Scott, Finlay^*,1, Grant, Alastair¹, ¹ University of East Anglia, Norwich, Norfolk, UK

ABSTRACT- Environmental variations (weather, toxin exposure, etc) alter demographic parameters of individuals. How do these perturbations feed through into effects on populations? Density dependence can reduce the effects of environmental stochasticity, but it is also possible for the two to interact in a way that amplifies the environmental noise, as in the case of Dungeness Crab and Soay Sheep. However, we lack a general framework to predict how populations will respond to environmental noise. Here we perturb two and three stage class population models, including the LPA model of Tribolium, with white noise, focussing on those parts of parameter space where the unperturbed population has a stable equilibrium. We assess responsiveness by measuring the variance of the input and output time series, and examine the ability of different elasticities to predict population responsiveness. The effect of these perturbations on the population can be characterised using elasticities. The elasticity of the density independent growth rate is effective as a general guide but for some forms of density dependence the one-step elasticity performs better. Density dependence may reduce impacts, but this depends crucially on its form and which parts of the life history are impacted by the environmental shocks. Short-term population consequences are sometimes greater than would be inferred from conventional elasticities. The extent to which this occurs can be predicted by the magnitude of the stability determining eigenvalue.

Key words: Dependence, Density, Elasticity, Perturbation