ABSTRACT
Environmental and climatic variables change greatly along an elevational gradient within a short distance, and since mountains often are among the last wilderness areas, they permit unbiased approaches toward an understanding of natural gradients of species richness (MacArthur, 1972; Walter, 1979; Körner, 2000; Fang, 2004). Many different elevational patterns of species richness have been reported (see Sanders et al., Chapter 10), often with a species richness peak at mid-elevations (Rahbek, 1995, 2005). However, such gradients often are confounded with region specifi c moisture (Körner, 2007) or land use gradients (Nagués-Bravo, 2008), leading to a reduction of species richness at lower elevations, unrelated to elevation, per se. On top of such nonstrictly elevationrelated drivers, the reduction of land area per elevational
belt exerts an additional, often unaccounted, driver of species richness (MacArthur, 1972; Bachman et al., 2004; Körner, 2000, 2007). Land area may even show a midelevation peak as well (Fu et al., 2006; Wang et al., 2007). Therefore, the elevational patterns should account for all drivers and separate physically elevation-related from particular regional patterns on top of the thermal gradient (Bhattarai et al., 2004; Fu et al., 2006). We argue, because other information often is limited, that elevational gradients of species richness should at least be adjusted for area (Bachman et al., 2004). Here we ask how this land area adjustment will affect species richness patterns by using electronic databases of species distribution and topography (geographical information systems, or GIS). The relationship between land area and species richness is one of the few well-established ecological rules, with larger areas supporting more species (Schoener, 1976), so area
Introduction ...................................................................................................................................................................49 Materials and Methods ..................................................................................................................................................50
