Habitat fragmentation can jeopardize the viability of natural populations by reducing the quality and the quantity of the genetic variation underlying important life history traits. This effect is in part due to the prevalence, in small and isolated populations, of random genetic processes especially random genetic drift, relative to non-random ones, particularly natural selection. Life-history traits such as competitive performance are critical fitness parameters and their decline due to habitat fragmentation exemplifies the risk of extinction for these populations. The primary objective of my study was to examine the impact of fragmentation on the quality of genetic variation underlying competitive performance in populations of Chamaecrista fasciculata. Competitive ability is a central fitness parameter for this species as it is an annual plant that has to compete successfully with perennials in prairies. By comparing populations of C. fasciculata, which vary in their population sizes and habitat fragment sizes, I examined whether there exists an inverse relationship between fragment size and competitive ability. I compared competitive performance of plants originating from twelve Illinois sand and tallgrass prairies that vary in their sizes; C. fasiculata population sizes were also variable. A common heterospecific competitor was used for the competition treatment, Schizarchirium scoparium (little bluestem). Competitive strength was evaluated on a set of traits at the early, middle and reproductive developmental stages of each plant. From the statistical analysis, it was shown that treatment, population effect and their interaction exerted a significant effect on a series of traits pertaining to early and later growth as well as reproduction. It appears that small and more isolated populations have suppressed levels particularly of mid and reproductive traits. This suggests that the quality of genetic variation underlying important components of competitive performance has been adversely affected in these populations.

Key words: Chamaecrista fasciculata, Competitive Ability, Genetic Drift, Habitat Fragmentation, Natural Selection, Prairies