Sensitivity analysis of equilibrium population Size in a density-dependent model for Short-tailed Shearwaters

Population models are often used to guide conservation management decisions. Sensitivity analysis of such models can be useful in setting research priorities, by highlighting those parameters that have the most influence on population growth rate. Much of the work on sensitivity analysis in this context has been for density-independent models. We present a sensitivity analysis of a density-dependent model for a population of Short-tailed Shearwaters (Puffinus tenuirostris), in which the output of interest is the equilibrium population size, N-e. We calculate the sensitivity and elasticity of N-e to both the equilibrium parameter value and the strength of density-dependence associated with each input parameter. The rankings of the sensitivities and elasticities associated with the strength of density-dependence are of particular interest, as they cannot be predicted from a. sensitivity analysis for the corresponding density-independent model. In calculating sensitivities we make use of the characteristic equation of the model, rather than the left and right eigenvectors of the projection matrix. In order to check the robustness of our conclusions to the strength of density-dependence specified for each input parameter, we consider a range of relative strengths. Within this range there are no major effects on the rankings. The largest sensitivities of N-e to the strength of density-dependence were for breeder survival, emigration and immigration; the largest corresponding elasticities were for emigration, immigration and breeder skipping rate. (C) 2003 Elsevier Science B.V. All rights reserved.