The Effects of Surrounding Vegetation and Transplant Age on the Detection of Local Adaptation in the Perennial Grass Aristida Stricta

1 A reciprocal-transplant experiment tested the hypothesis that two populations of a perennial grass were locally adapted. Because population differentiation might be due to differential adaptation to the presence of surrounding vegetation, plants were transplanted into undisturbed areas and areas from which surrounding vegetation had been removed. As an indirect investigation of the effects of temporal environmental heterogeneity on the detection of local adaptation, three age-classes of plants were included in the experiment. 2 Seeds collected from the two populations were sown into soil from both sites in the greenhouse. Seedlings of three age-classes were transplanted reciprocally between the two field sites into both undisturbed quadrats and quadrats from which vegetation had been removed. Seedling survival was recorded for six months, and dry weight was determined for all seedlings that survived to the end of this period. 3 Comparisons of seedling survival and biomass revealed evidence for local adaptation, and the expression of local adaptation was affected very little by the presence of surrounding vegetation. Results for vegetation-removal quadrats closely paralleled those for unmanipulated quadrats. This result does not support the hypothesis that the two populations are differentiated with respect to performance in the presence of vegetation. 4 The detection of local adaptation depended strongly on the age of transplants. Home-site survival and final biomass advantages were greater for older age-classes. The effect of transplant age on the detection of population differentiation suggests that evidence of population differentiation may not always be apparent because of temporal variation in environmental conditions.