Perennation and the Persistence of Annual Life Histories

Individuals of Eriogonum abertianum that live for more than a year in the wild (perennators) have offspring that live longer under greenhouse conditions than do the offspring of the general population. This suggests some genetic basis to the occasional perennation observed in the wild. Longevity appears to be continuously distributed, with the perennators representing the tail of the population's distribution. Could such apparent genetic variation for life-history traits potentially lead to the evolution of a perennial or biennial population? I examined the persistence of the annual habit using Lande's model of life-history evolution and a model of size-dependent demography. Results suggest that for populations with very low adult survival rates, selection generally acts to increase fecundity and the proportion of individuals surviving to maturity, thereby reducing perennation. The annual habit is thus likely to persist even in the presence of genetic variation for perennation.