Ecological Differentiation Among Populations of Three Alvar Plant Species: Linking Traits to Growth in a Common Garden

Populations in fragmented habitat patches may show ecological differentiation, which has implications for metapopulation viability. In this study we used a common garden with two watering treatments to contrast mean differences in ecophysiological traits and the relationships between traits and performance among seven populations of three alvar species. These species differ in their alvar specialization in Ontario, from almost endemic (Solidago ptarmicoides) to highly confined (Dasiphora fruticosa) to a widespread generalist (Hypericum perforatum). Populations of all species exhibited mean differences in at least one trait: photosynthesis (Amax), growth rate and specific leaf area. More surprisingly, the relationship between functional traits and performance was significantly different among populations in all species, suggesting different strategies for maximizing growth in different environments. The ecological differentiation observed affected all species regardless of distribution and is likely genetically based. This differentiation may destabilize metapopulation dynamics and reduce rates of spread if colonization is negatively impacted.MAS