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 po pulations of a perennial grass were locally adapted. Because populatio n differentiation might be due to differential adaptation to the prese nce of surrounding vegetation, plants were transplanted into undisturb ed 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 betwee n 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 surv ived 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 surround ing vegetation. Results for vegetation-removal quadrats closely parall eled those for unmanipulated quadrats. This result does not support th e 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 sur vival and final biomass advantages were greater for older age-classes. The effect of transplant age on the detection of population different iation suggests that evidence of population differentiation may not al ways be apparent because of temporal variation in environmental condit ions.