Species richness and endemism of plant and bird communities along two gradients of elevation, humidity and land use in the Bolivian Andes

Abstract

Abstract.We studied the patterns of species richness and range–size rarity (as a measure of endemism) of two plant groups (Pteridophyta, Bromeliaceae) and birds along two gradients of elevation, humidity and human land use in a forested Andean valley. Both transects covered the transition from an arid valley bottom through a cloud forest zone to relictual high‐elevation Polylepis forest, but transects differed in overall precipitation. Plants were surveyed in 88 plots of 400 m2 each, while birds were detected primarily through visual observations and tape recordings over areas of 0.3–1.5 km2. Global range sizes of all species were mapped on 1°‐grids and range‐size rarity was calculated as the mean inverse range size of all species recorded in elevational steps of 200 m. Patterns of species richness and range–size rarity were mainly unrelated between and within study groups. Monotonic increases and decreases and hump‐shaped patterns were observed for species richness as well as range–size rarity. Several of these patterns can be interpreted in the light of the ecological requirements of each taxonomic group, e.g. dependence of fern species richness on humidity or of bird richness on habitat complexity. Species richness of ferns and birds peaked at higher elevations along the less rainy transect, possibly as a result of higher levels of solar radiation and ecosystem productivity. Patterns of species richness and endemism of the study groups are causally unrelated and cannot be used to predict those of other groups at the spatial scale of this study. Human impact was highest in areas of mostly low to intermediate species richness, but was often high in zones of high endemism.

Bird community structure in natural and urbanized habitats along an altitudinal gradient in Pauri district (Garhwal Himalaya) of Uttarakhand state, India

“…The pattern of the avian community of the present study varies from that reported by many previous studies conducted on bird species richness along altitudinal gradients mostly in temperate regions. Most such studies have found the highest species richness at low elevation such as in rain forest of eastern Andes Peru (Terborgh 1971;Terborgh & Weske 1975) or mid elevation such as in Peruvian Andes (Rahbek 1995(Rahbek , 2005, Madagascan rain forest (Colwell & Lees 2000), Bolwian Andes South American Forest (Kessler et al 2001), Columbian Andes forest (Kattan & Franco 2004), urban/subtropical to subarctic forest in Taiwan (Lee et al 2004;Ding et al 2005). In the present study the higher BSD and BSR observed in high altitude areas may be connected to the higher plant diversity.…”

The Humpbacked Species Richness-Curve: A Contingent Rule for Community Ecology

“…Organisms showing mid-elevation peaks in species richness include epiphytic ferns [58], vascular plants and lichens [59], moths [60], ants [61,62], birds [58,63], and small mammals [64]. The reasons for these patterns are varied and difficult to disentangle.…”

“…According to Kessler et al [58], for example, the mid-elevation peak in bird and epiphytic fern diversity in the Bolivian Andes coincides with peaks in primary productivity, foliage height (i.e., spatial heterogeneity), and land use (i.e., disturbance).…”

Diversity of Millipedes in Alagar Hills Reserve Forest in Tamil Nadu, India

“…Rahbek [7] demonstrated that hump-shaped relationship with maximum species numbers at midelevations. Different elevational richness pattern may be due to (a) an overall decline of species richness with increasing altitude [33], (b) a plateau of species being the richest at lower altitude then declining towards the highest elevations [34], and (c) a midelevation peak of species richness [35,36]. Padmanaban [18] reported that cockroach diversity and abundance were the maximum in the middle altitudes in comparison with those in the higher and lower altitudes of Alagar hills reserve forest., Isabel [23] also emphasized that arthropod species diversity was higher in midelevations compared to that in lower and higher elevations of Alagar hills.…”