群落生态学的中性理论

NEUTRAL THEORY IN COMMUNITY ECOLOGY

生物多样性的分布格局和维持机制一直是群落生态学研究的核心问题,其中的关键是物种的共存机制。长期以来,生态位分化的思想在这一研究领域占据着主导地位。然而这一理论在解释热带雨林很高的物种多样性时遇到了困难。而以Hubbell为代表提出的群落中性漂变理论则假定在同一营养级物种构成的群落中不同物种的不同个体在生态学上可看成是完全等同的;物种的多度随机游走,群落中的物种数取决于物种灭绝和物种迁入/新物种形成之间的动态平衡。在这一假定之下,该理论预言了两种统计分布。一种是集合群落在点突变形成新物种的模式下其各个物种相对多度服从对数级数分布,而受扩散限制的局域群落以及按照随机分裂为新物种模式形成的集合群落则服从零和多项式分布。与生态位理论相反,中性理论不以种间生态位差异作为研究群落结构的出发点,而是以物种间在个体水平上的对等性作为前提。该理论第一次从基本生态学过程(出生、死亡、迁移、物种分化)出发,给出了群落物种多度分布的机理性解释,同时其预测的物种多度分布格局在实际群落中也得到了广泛的印证。因此,中性理论自诞生以来便在生态学界引发了极大的反响,也包括一些反对的声音。该文重点综述了关于中性理论的假设、预测和物种形成模式等方面的最新研究进展,包括中性理论本身的发展、关于中性理论的假设和预测的合理性检验以及在集合群落尺度上物种分化模式的讨论;并指出未来发展方向可能是在生态位理论和中性理论之间架起一座桥梁,同时发展包含随机性的群落生态位模型,以及允许种间差异的近中性模型。

A central goal of community ecology is to understand the forces that maintain species diversity within communities, rFne traditional niche-assembly theory asserts that species co-occur in a community only when they differ from one another in resource use. But this theory has some difficulties to explaining the diversity often observed in species-rich communities such as tropical forests. As an alternative to niche theory, Hubbell and other ecologists introduced a neutral model. Hubbell argues that the number of species in a community is controlled by species extinction and immigration and speciation of new species. Assuming that all individuals of all species in a trophically similar community are ecologically equivalent, Hubbell＇ s neutral theory predicts two important statistical distributions. One is the asymptotic log-series distribution for the metacommunity under point mutation speciation, and the other is the zero-sum multinomial distribution for both local community under dispersal limitation and metacommunity under random fission speciation. Unlike the niche-assembly theory, the neutral theory takes similarity in species and individuals as a departure for investigating species diversity. Based on the fundamental processes of birth, death, dispersal and speciation, the neutral theory first presented a mechanism that generates species abundance distributions remarkably similar to those observed in nature. Since the publication of the neutral theory, there has been much discussion of it, pro and con. In this paper, we summarize new progresses in research on assumption, prediction and speciation mode of neutral theory, including progress in the theory itself and tests about the theory＇ s assumption, prediction and speciation mode at metacommunity level. We also suggest that the most important task in the future is to bridge the niche-assembly theory and the neutral theory, and to add niche-differences in neutral theory and more stochasticity into niche theory.