Despite numerous theoretical studies on evolution in heterogeneous environments and empirical studies of genotype- environment interactions, patterns of variation in the selective environment have been largely ignored by evolutionary biologists. Theoretical studies have shown that the results of natural selection in heterogeneous environments depend critically on the spatial and temporal scale of heterogeneity in the selective environment. The selective environment is define by changes rank order of fitness among genotypes (genotype-environment interactions). The investigators will examine spatial and temporal heterogeneity of selection in an oldfield population of Erigeron annuus, using three replicated asexual genotypes as "photometers" to measure environmental heterogeneity. Seedlings of the three genotypes will be planted in a sample grid and monitored for survivorship and fecundity. Areas of positive spatial autocorrelation of relative fitness will define the selective patch, and this will be compared to variation in the physical environment. This research will result in the first map of the selective landscape and will show temporal changes in the selective surface during succession.
