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While horizontal gradients of biodiversity have been examined extensively in the past, vertical diversity gradients (elevation, water depth) are attracting increasing attention. We compiled data from 443 elevational gradients involving diverse organisms worldwide to investigate how elevational diversity patterns may vary between the Northern and Southern hemispheres and across latitudes. Our results show that most elevational diversity curves are positively skewed (maximum diversity below the middle of the gradient) and the elevation of the peak in diversity increases with the elevation of lower sampling limits and to a lesser extent with upper limit. Mountains with greater elevational extents, and taxonomic groups that are more inclusive, show proportionally more unimodal patterns whereas other ranges and taxa show highly variable gradients. The two hemispheres share some interesting similarities but also remarkable differences, likely reflecting differences in landmass and mountain configurations. Different taxonomic groups exhibit diversity peaks at different elevations, probably reflecting both physical and physiological constraints. Montane regions harbor more than half of the world's biodiversity hotspots and recent research on biodiversity patterns has been notable for an increase in research on elevational patterns on mountains 1 . Mountains provide unique opportunities as 'natural experiments' for testing ecological theories and in particular for studying the effects of climate change because they present gradients in key abiotic features such as temperature and available moisture. Recent efforts have generated interesting and sometimes conflicting results, and debates on the generality of the frequently observed unimodal (''hump-shaped'' 2 ) curves and the underlying mechanisms have not been fully resolved. Indeed, despite increased research in this area in recent years, employing markedly improved techniques and greater sampling intensity, much inconsistency and debate remains both in pattern description and interpretation. For example, surprisingly little effort has targeted how elevational diversity patterns might vary in the Northern and Southern hemispheres and across latitudinal zones [3][4][5][6][7] . To tackle these problems, detailed comparisons are needed over distinct (replicate) elevational gradients across the globe.The upper elevational limit for phanerogams varies as a function of latitude and generally reflects limits to physiologic tolerance 1 . Moreover, similar elevational ranges in different regions are likely to exhibit different underlying gradients 8 , reflecting regional climate and geography; cold-temperate mountains lack the warm climate characteristic of lower elevations at lower latitudes, and temperatures at a tropical treeline might reflect those at the base of cold-temperate mountains. Additionally, the effect of aspect is greatly reduced on tropical mountains relative to temperate ones. As a result of these latitudinal differences, structurally identical mountains locate...
The relationship between species richness and biomass is and has been one of the most controversial subjects in ecology. This paper examines these relationships from the perspectives of habitat heterogeneity and environmental gradients measured within and cross five microhabitat types. Species richness, aboveground biomass, and their relationships were compared in two ways: with samples aggregated by microhabitat type, and with analysis of all microhabitat types. Within microhabitat types, in which the environment was relatively homogeneous, we found the species richness–biomass relationship to be positive, negative, or non‐existent. The relationship is positive when biomass is low (in open and half‐shrub microhabitats) and negative when it exceeds a certain level (e.g., under shrubs). When the sample area encompassed different microhabitat types, a “hump‐shaped” relationship was detected. The mechanisms underlying these observed patterns are discussed from the perspectives of environmental gradients and competition.
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