The elevational gradient in Andean bird species richness at the local scale: a foothill peak and a high‐elevation plateau

Abstract

K. 2005. The elevational gradient in Andean bird species richness at the local scale: a foothill peak and a high-elevation plateau. Á/ Ecography 28: 209 Á/222.A monotonic decline in species richness with increasing elevation has often been considered a general pattern, but recent evidence suggests that the dominant pattern is hump-shaped with maximum richness occurring at some mid-elevation point. To analyse the relationship between species richness and elevation at a local scale we surveyed birds from lowlands to timberline in the Bolivian Andes. We divided the transect into 12 elevational belts of 250 m and standardized species richness in each belt with both individual-and sample-based rarefaction and richness estimation. The empirical data were then correlated to four explanatory variables: 1) area per elevational belt, 2) elevation (also representing ecosystem productivity), 3) a middomain effect (MDE) null model of geometrically constrained empirical range sizes, and 4) a hump-shaped model derived empirically for South American birds representing the regional species pool hypothesis. Local species richness peaked at ca 1000 m elevation, declined sharply to ca 1750 m, and then remained roughly constant. Elevation was the best single predictor, accounting for 78 Á/85% of the variance in the empirical data. A multiple regression model with elevation, area, and MDE explained 85 Á/90% of the variance. Monte Carlo simulations showed that the richness peak at 1000 m is the result of an overlap of two distinct avifaunas (lowland and highland) and that the correlation to MDE in the multiple regression was likely spurious. We recommend complementing correlation analyses involving MDE predictions with an examination of the distribution of range midpoints. The steep decline at mid-elevations was mainly due to a rapid loss of lowland species. The high-elevation plateau is striking and unexpected, but has also been found previously. It cannot be explained at present and exemplifies that despite several decades of research elevational gradients are still not well understood.S. K. Herzog (skherzog@compuserve.com), Inst. fü r Vogelforschung ''Vogelwarte

Elevational patterns of species richness and density of rattan palms (Arecaceae: Calamoideae) in Central Sulawesi, Indonesia

“…In New Guinea, variation in hump-shaped pattern of palm species richness has been linked to the middomain effect (Bachmann et al 2004), but the biological reality of this effect is commonly questioned (Currie and Kerr 2008). In our study region, many species overlap in their upper or lower elevational limits at 1000 and 1100 m, which may also increase species richness here, but runs contrary to the assumptions of the mid-domain effect which is based on random species distributions (Herzog et al 2005;Kluge et al 2008). The high species richness at mid-elevation could be also related to a lower canopy height (Siebert 2005), because rattan individuals can reach higher light intensities more easily.…”

Altitudinal distribution of bats in the Pol’ana Mts area (Central Slovakia)

“…A monotonic decline in species richness and density with increasing elevation has often been considered a general pattern, but recent evidence suggests that the dominant pattern is hump-shaped with maximum richness occurring at some mid-elevation point (Colwell et al, 2005;Herzog et al, 2005). In our study at a local scale from oak to spruce vegetation stages (350-1350 m a.s.l.)…”

Density compensation, species composition, and richness of ants on a neotropical elevational gradient

“…Typically, studies of assemblage (alpha) diversity along elevational gradients quantify or estimate species richness of assemblages as a function of elevation, then seek environmental or historical variables that best explain those patterns statistically (McCoy 1990, Samson et al 1997, Pyrcz and Wojtusiak 2002, Sanders 2002, Sanders et al 2003, McCain 2005, 2007a, 2007b, Herzog et al 2005, Oommen and Shanker 2005, Grytnes and Beaman 2006, Kluge et al 2006, Brehm et al 2007, Beck and Chey 2008, Kumar et al 2009. Between sea level and mountain-tops, richness may show a monotonic decline, a midelevation peak, or less often a more complex pattern (Rahbek 1995, McCain 2009.…”