Natural populations which have been surveyed exhibit large amounts of genetic diversity, i.e., differences in the genetic makeup between individuals. This variability allows the population to respond to a changing environment. Variability is crucial to a population because it allows a population to evolve. Differences in the environment through time and space are thought to be two primary factors maintaining this genetic variability. Spatial heterogeneity is common in a range of environments and has been shown to support genetic variability. Particular individuals are often better adapted to their microenvironment, thus the population as a whole is comprised of many individuals adapted to slightly different environments. The investigators will experimentally test if individuals of a population are better adapted to particular seasons. By determining whether individuals grow and reproduce better at different times within the year, they can test the notion that temporal as well as spatial differences in the environment are important in maintaining genetic diversity. No experiments using plants have explicitly tested the importance of environmental differences among seasons or years. In addition to understanding underlying mechanisms supporting genetic diversity, knowledge of the seasonality of plant populations may be of practical benefit. Efficacy of herbicide applications, for example, is partially a function of when during the plant life-cycle an herbicide is applied. Additionally, if a population represents an array of genotypes adapted to different seasons, particular individuals or populations may have the ability to persist in or be "preadapted" to an altered environment. A population's response to a global environmental change such as warming maybe predicted. Predictions of extinction or genetic change by populations may then be used to examine potential shifts in species composition of communities and ecosystems.
