α, β and γ-diversity of vascular epiphytes along the climatic gradient of continental Chile

The global diversity of vascular plants markedly decreases from the tropics to temperate zones; however, along the South American climatic gradient from Mediterranean to temperate climates, vascular epiphytes exhibit a secondary pattern in which species richness increases towards temperate rainforest. In this region, large-scale ecological studies have usually not recognised epiphytes as a distinct floristic element, so relationships of epiphyte community composition and diversity with regional climate are poorly understood. We used georeferenced herbarium data to describe the richness (alpha and gamma-diversity) and turnover (beta(tau)-diversity) of vascular epiphytes, and evaluated the relationship of species richness and community composition with climatic variables in the arid, Mediterranean and temperate zones of Chile. Our results indicate that alpha, beta(tau) and gamma-diversity patterns vary widely along the environmental gradient. alpha-diversity has a unimodal distribution curve with maximum values between 38 degrees S and 47 degrees S. In the arid region occupying the northern part of the gradient (17 degrees S-28 degrees S), abrupt changes in species composition (beta(tau)-diversity) reflect the environmental heterogeneity of the zone, where epiphyte occurrence is restricted to isolated sites where water availability depends on fog. In temperate climates further south, where spatial and temporal availability of water is more continuous, species' distributions overlap widely, leading to a decrease in beta tau values. Calculated as the product of the alpha-diversity and beta(tau) values, gamma-diversity increases with latitude, reaching its maximum in the temperate forest region between 38 degrees S and 47 degrees S, in accordance with previous descriptions for vascular epiphytes. The influence of alpha and beta(tau)-diversity on gamma-diversity changes along the gradient: beta(tau)-diversity is more critical in desert and Mediterranean climates, while the contribution of alpha-diversity increases towards temperate climates.