10 - ENSEMBLE QUANTITIES: VARIABILITY

Abstract

This chapter describes that variability is a quantity subject to loss and gain. The view of variability distinguishes biology from the other natural sciences. Genetic variability is the raw material on which natural selection operates to generate new species. Variability in other ecological quantities is of just as much interest, whether the quantity is density, production rate, or a biogeochemical flux. Variability is measured by an ensemble quantity called a deviance, which is the weighted sum of the deviations of individual values from an average. Any weighting scheme can be used. One of the most commonly encountered is to weight deviations according to their own magnitude, resulting in a variance var (Q ) . The variance is viewed as an interpretable quantity, which is often of more interest than the average or summed value of an ecological quantity simply because of the highly variable response of natural populations to heterogeneous environments.