科研之友
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摘要
Ecologists usually estimate means, but devote much less attention to variation. The study of variation is a key aspect to understand natural systems and to make predictions regarding them. In community ecology, most studies focus on local species diversity (alpha diversity), but only in recent decades have ecologists devoted proper attention to variation in community composition among sites (beta diversity). This is in spite of the fact that the first attempts to estimate beta diversity date back to the pioneering work by Koch and Whittaker in the 1950s. Progress in the last decade has been made in the development both of methods and of hypotheses about the origin and maintenance of variation in community composition. For instance, methods are available to partition total diversity in a region (gamma diversity), in a local component (alpha), and several beta diversities, each corresponding to one scale in a hierarchy. The popularization of the so-called raw-data approach (based on partial constrained ordination techniques) and the distance-based approach (based on correlation of dissimilarity/distance matrices) have allowed many ecologists to address current hypotheses about beta diversity patterns. Overall, these hypotheses are based on niche and neutral theory, accounting for the relative roles of environmental and spatial processes (or a combination of them) in shaping metacommunities. Recent studies have addressed these issues on a variety of spatial and temporal scales, habitats and taxonomic groups. Moreover, life history and functional traits of species such as dispersal abilities and rarity have begun to be considered in studies of beta diversity. In this article we briefly review some of these new tools and approaches developed in recent years, and illustrate them by using case studies in aquatic ecosystems. Ec車logos geralmente estimam m谷dias, mas dedicam pouca aten o 角 varia o. O estudo da varia o 谷 um aspecto chave para entender sistemas naturais e fazer predi es. Em ecologia de comunidades, a maioria dos estudos foca na diversidade local de esp谷cies (diversidade alfa), e apenas recentemente ec車logos passaram a dar aten o apropriada a varia o na composi o de comunidades entre s赤tios amostrais (diversidade beta). Isto acontece apesar do fato das primeiras tentativas de estimar diversidade beta terem sido feitas pelos trabalhos pioneiros de Koch e Whittaker na d谷cada de 1950. Houve significativo progresso na 迆ltima d谷cada no desenvolvimento tanto de m谷todos como de hip車teses sobre a origem e manuten o da varia o na composi o de comunid
