The abundances of many plant species fluctuate widely in natural populations. Close examination of some of the most simple mathematical models of population growth has shown that in addition to the effects of random environmental noise, fluctuations in population size (from periodic oscillations to chaos) may be part of the natural dynamics of many systems. These theoretical results are seldom tested because multi- generation experiments in controlled environments are often difficult and expensive to conduct. The investigators will use experimental populations to examine 15 generations of the population dynamics of Cardamine pennsylvanica, a small, rapidly- growing greenhouse weed. Using a greenhouse weed allows them to do experiments in ecologically "natural" conditions with the precision and ease of a controlled environment. Population dynamics may be affected by different environments. Hence, some experimental populations will have variable environments and others will not. Population dynamics may be affected by the genetics of the population. Hence, some experimental populations will have little genetic variability and others will have substantial genetic variability. Genetically uniform populations may be expected to evolve little, and exhibit purely ecological responses. These experiments are essential steps toward understanding to what extent populations dynamics are driven by ecological versus genetic processes.
