Dr. Bruce Kendall (Bren School of Environmental Science and Management, UCSB)

Title: Population consequences of individual heterogeneity in demography and growth

Abstract: Variation in phenotypic traits occurs within all populations. This, in turn, creates variation in demographic traits — the propensity to be more or less likely to survive, or to have more or fewer offspring. While ecologists do use models (like linear matrix models) that classify individuals by age, stage or size, and sex, most assume that in doing so they have captured sufficient variation, so that further variation is simply noise of small amplitude. This is not necessarily the case. This variation in traits occurs even when within categories such as age, stage, size, or sex. Demographic heterogeneity can result from a number of causes that are not mutually exclusive, including genetic variation, spatial or temporal environmental variation, phenotypic plasticity, and heteromorphisms.

Demographic heterogeneity has at least three effects. First, it affects the amount of demographic stochasticity experienced by populations, and thereby the risk of extinction. Second, under a number of circumstances, lineages with demographic heteromorphisms are favored by selection as a means of maximizing the chance of lineage persistence in the face of demographic stochasticity; these conditions are different from those favoring heteromorphisms as a strategy of bet-hedging against environmental stochasticity. Third, the dynamics of heterogeneous populations are different from those of homogeneous populations, especially in the face of spatial and temporal variation.