Patterns of Neotropical Epiphyte Diversity

The authors have made extensive investigations on vascular epiphytes in the last 20 years, particularly on epiphytic vegetation in four tropical montane forest sites. These are Sehuencas (Bolivia); Otonga and Rio Guajalito (Ecuador); and La Carbonera and the Amazonian lowland forest crane plot at Rio Surumoni (Venezuela). Based on these studies, they analyze the systematic compositions and vertical and horizontal distribution patterns of epiphytes at the sites. Orchids are the most species-rich of all local epiphyte vegetation. At lowland sites, Araceae are particularly diverse. Vertical zonation of epiphytes in the canopy is a result of different ecophysiological traits. Despite marked preference for certain strata in some taxa, overlap is considerable. The differences in epiphyte diversities of montane and lowland forests can be explained by different distribution patterns. For example, in montane forests with high alpha diversity of epiphytes, species turnover between sites separated by a small geographical distance is considerable. In contrast, alpha diversity of epiphytes in the Amazonian lowlands is low, but the number of epiphyte species increases gradually with area. Although lowland forests cover vast areas, the overall epiphyte species richness is no higher than that of the wet Andean montane forests, which occupy a far smaller land surface. A tentative explanation of these differences in distribution patterns assumes different evolutionary scenarios. In the Andes, where geographical separation frequently has isolated gene pools, ecologically similar species occupy different areas. In the Amazonian lowlands, where considerable gene flow results from the mixing of populations by dispersal of diaspores and effective pollinators, fewer species have evolved. Dispersal and pollination tend to be highly effective in epiphytes because of their adaptation to the epiphytic habitat. The striking differences in diversity patterns have resulted from their evolution, which may have followed a specific path compared to terrestrial plants.