Life expectancy change in perturbed communities: derivation and qualitative analysis

Pollution, loss of habitat, and climate change are introducing dramatic perturbations to natural communities and affecting public health. Populations in perturbed communities can change dynamically, in both abundance and age structure. While analysis of the community matrix can predict changes in population abundance arising from a sustained or press perturbation, perturbations also have the potential to modify life expectancy, which adds yet another means to falsify experimental hypotheses and to monitor management interventions in natural systems. In some instances, an input to a community will produce no change in the abundance of a population but create a major shift in its mean age. We present an analysis of change in both abundance and life expectancy, leading to a formal quantitative assessment as well as qualitative predictions, and illustrate the usefulness of the technique through general examples relating to vector-borne disease and fisheries.