RESPONSE TO DENSITY IN A WILD POPULATION OF THE PERENNIAL HERB SALVIA LYRATA: VARIATION AMONG FAMILIES.

In order to determine the potential for natural selection to promote genetic specialization to different environments, this study quantified genetic variation for response to conspecific density and to other aspects of the environment that vary spatially. The progeny of a random collection of Salvia lyrata, a perennial herb, were planted into the source field in a range of densities and into several closely neighboring locations. The highest density and particular locations induced significantly greater mortality relative to the remaining densities and locations, indicating major effects of density and spatial location on fitness. Over the duration of the entire study, there was also significant variation among families in mortality. The survival data gave no indication of variation among families in their responses to the range of environments. Conversely, results based on growth and size indicated that different families were favored in different densities and locations, in support of the hypothesis that environment-dependent selection promotes specialization to different environments in this species. The correlation among families between leaf number in high and low density was small and positive, indicating near-independence of performance in different densities.