Abstract
The net reproductive rate, R_0, is the expectation of lifetime reproductive output. It can be calculated from age- or stage-classified demographic models, and is important in demography, evolutionary biology, and epidemiology. But R_0 is not the whole story. Studies on a variety of organisms routinely reveal wide variation around R_0. This variation is often taken as evidence of heterogeneity (genetic or otherwise) and interpreted as an opportunity for selection to operate. However, there has been no way to calculate the variability in lifetime reproductive output implied by a given demographic model. Now, there is. This talk will present some recent results, based on Markov chain theory, that make it possible to go beyond R_0 and compute the variance and skewness of lifetime reproduction, from age- or stage-classified matrix population models, in constant, periodic, or stochastic environments. Some examples, from animal and plant populations, suggest the existence of some interesting patterns that deserve further study.