Lack of ecotypic differentiation: Plant response to elevation, population origin, and wind in the Luquillo Mountains, Puerto Rico

How important is ecotypic differentiation along elevational gradients in th e tropics? Reciprocal transplants of two shrubs, Clibadium erosum (Asterace ae) and Psychotria berteriana (Rubiaceae), and a palm, Prestoea acuminata v ar. montana (Palmaceae), were used to test for the effect of environment an d population origin on growth and physiology in the Luquillo Experimental F orest of Puerto Rico. Two sites were used, one at Pico del Este (1000 m in cloud forest) and one at El Verde (350 m in lower montane rain forest). At the cloud forest site, plastic barriers were erected around a subset of the plants to examine if protection from wind affected survival or biomass acc umulation. Survival of C. erosum and P. berteriana was nor affected by site , population origin, or the presence of barriers. For P. acuminata var. mon tana, survival was higher for plants with barriers, but not affected by sit e and population origin. Plants of C. erosum and P. berteriana at El Verde grew larger than at Pico del Este, but there was no effect of population or igin or barrier treatment on biomass accumulation for these species. For 1! acuminata var. montana, there was no effect of environment, population ori gin, or barrier treatment on biomass accumulation. Light-saturated photosyn thetic rare (A(max)) of C. erosum, P. berteriana, and P. acuminata var. mon tana, as well as leaf anatomical characteristics of C. erosum, were unaffec ted by environment, population origin, and barrier treatment. On balance, t here seems to be little evidence of ecotypic differentiation in these speci es along the gradient.