Lack of Ecotypic Differentiation: Plant Response to Elevation, Population Origin, and Wind in the Luquillo Mountains, Puerto Rico1

Abstract

How important is ecotypic differentiation along elevational gradients in the tropics? Reciprocal transplants of two shrubs, Clibadium erosum (Asteraceae) and Psychotria berteriana (Rubiaceae), and a palm, Prestoea acuminata var. montana (Palmaceae), were used to test for the effect of environment and population origin on growth and physiology in the Luquillo Experimental Forest 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 accumulation. Survival of C. erosum and P. berteriana was not affected by site, population origin, or the presence of barriers. For P. acuminata var. montana, survival was higher for plants with barriers, but not affected by site 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 origin or barrier treatment on biomass accumulation for these species. For P. acuminata var. montana, there was no effect of environment, population origin, or barrier treatment on biomass accumulation. Light-saturated photosynthetic rate (Amax) of C. erosum, P. berteriana, and P. acuminata var. montana, as well as leaf anatomical characteristics of C. erosum, were unaffected by environment, population origin, and barrier treatment. On balance, there seems to be little evidence of ecotypic differentiation in these species along the gradient.