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1、群落构建的中性理论和生态位理论群落构建的中性理论和生态位理论牛克昌1* 刘怿宁1 沈泽昊1 何芳良2 方精云11 (北京大学城市与环境学院生态学系, 北京大学地表过程分析与模拟教育部重点实验室, 北京 100871) 2 (Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2H1)摘要: 物种共存和生物多样性维持一直是生态学研究的中心论题。基于物种生态位分化的群落构建理论已经发展了近一个世纪, 但我们对群落构建和生物多样性维持的机理仍然不清楚。近年来, 群落中性理论以其
2、简约性和预测能力成为群落生态学研究的焦点, 但由于其物种在生态功能上等价的假设与大量研究结果相悖, 同时对自然群落结构的准确预测也只限于少数的生态系统, 因而饱受质疑。如今, 越来越多的生态学家认为群落构建的生态位理论与中性理论之争的最终归宿应该是二者的整合。 在本文中, 我们在简要回顾生态位理论和群落中性理论发展的基础上, 分析二者之间的主要分歧和互补性, 试图梳理二者整合的途径。我们认为, 尽管中性理论的发展极大地丰富了群落构建理论, 但二者的整合尚处于初级阶段; 群落构建零模型假说、中性-生态位连续体假说、随机生态位假说等都不失为有价值的尝试, 今后需要在其他类型的生态系统中进行实验验证
3、, 以更好地理解确定性过程和随机过程在决定群落构建和生物多样性维持中的作用。关键词: 物种特征, 生态等价, 随机, 物种相对多度, 物种多度分布Community assembly: the relative importance of neutral theory and niche theoryKechang Niu1*, Yining Liu1, Zehao Shen1, Fangliang He2, Jingyun Fang1 1 Department of Ecology, College of Urban and Environmental Sciences and Key La
4、boratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China2 Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2H1Abstract: Understanding species coexistence and the maintenance of biodiversity has long been the ce
5、ntral interest of ecologists. The niche-based theory of community assembly has dominated community ecology for nearly a century, yet understanding of the mechanisms of species coexistence has remained elusive. The newly developed neutral theory of biodiversity has offered a promising alternative to
6、the niche paradigm. The analytical elegance and simplicity of the neutral theory and its predictive power have made the theory widely popular. However, it is the very same simplicity of the theory (e.g. the symmetric assumption) that makes the theory vulnerable to stark criticisms. Widespread empiri
7、cal evidence has shown that species in communities are not functionally symmetric; ecological equivalence is more a conceptual simplicity than a biological realism. Recognizing that niche and neutral processes do not have to diametrically oppose each other and a community is likely determined by the
8、 interplay of the two processes, ecologists currently are searching to reconcile the two theories by either incorporating drift into niche theory or niche into the neutral framework. However, this reconciliation process is still at its very early stage, we expect this direction will lead to a more c
9、omplete understanding of community assembly mechanisms. In this paper, we provide a review on the brief histories of the niche and neutral theories, with the focus on comparing the distinct importance of the two theories in explaining community assembly. We discuss in details several integrated mode
10、ls that attempt to unify the niche and neutral theories. We argue that it is an essential step for any successful theory to withstand substantial experimental and field tests. The experimental tests of neutral theories are an important direction that has currently not received due attention.Key word
11、s: species traits, ecological equivalence, stochasticity, species relative abundance, species abundance distribution一个多世纪以来, 生物多样性的形成和维持机理即群落构建(community assembly)机制一直是生态学研究的核心论题。传统的观点认为, 各物种特征的权衡(trade-offs)和组合的不同决定了其生活史对策(life historical strategy, 如资源利用方式)的不同, 由此决定了各物种在群落中所占有的生态位(niche)不同, 进而决定了多物
12、种的稳定共存(Hutchinson, 1959; Vandermeer, 1972; Silvertown, 2004)。也就是说, 物种在群落中的共存是以生态位的分化为前提的, 生态位相同的物种可能因竞争共同的资源而发生竞争排除, 不能稳定共存(Vandermeer, 1972)。然而, 当解释生境中限制性资源不多, 多物种生态位分化不明显, 而依然稳定同存的现象(如热带雨林)时, 传统的生态位构建理论遇到了巨大的挑战(Bell, 2000; Hubbell, 2001)。并且, 以生态位理论为基础的确定性因素无法有效地预测群落结构动态, 使得许多生态学家开始考虑非确定性因子的作用。以Hub
13、bell为代表的生态学家根据种群遗传学的中性理论(neutral theory), 提出了群落中性理论(Bell, 2000; Hubbell, 2001)。群落中性理论以其简约性和可预测能力迅速赢得许多生态学家的青睐, 成为过去10多年来最受关注的生态学理论热点(Volkov et al., 2003; Chave, 2004; Alonso et al., 2006; Holt, 2006)。一些生态学家甚至认为, 群落中性理论是将生物多样性和生物地理学相统一的理论(Hubbell, 2001; Bell, 2003)。然而, 大量的实验研究表明, 群落各物种并非如中性理论所假设的那样在生
14、态功能上等价(functional equivalence), 基于功能性状的物种生态位分化和种间作用在群落构建和多样性维持中有着决定性作用(Harpole & Tilman, 2006; Kraft et al., 2008); 而且由于中性理论的模型中群落大小难以界定, 物种分化速率、迁移率和死亡率等各参数可变性很大, 而模型模拟结果对这些参数设置的变化又极其敏感(Zhang & Lin, 1997; Yu et al., 1998), 因而该理论对群落结构的预测也只能是微弱的(weak test)(Wootton, 2005; McGill et al., 2006)。因此, 最近几年来
15、, 越来越多的生态学家倾向于认为, 在群落构建中生态位理论和中性理论并非对立, 将生态位理论和中性理论整合可以更好地理解群落构建的机理(Tilman, 2004; Chase, 2005; Gravel et al., 2006; Leibold & McPeek, 2006)。本文试图在简要回顾群落中性理论和生态位理论发展的基础上, 梳理其最新研究进展, 并探讨整合生态位理论和中性理论, 解释群落构建和多样性维持的可能途径。 1 群落构建的生态位理论关于群落多样性的形成和维持机理, 主要存在两类不同的观点。一种观点认为, 在群落构建和多样性维持中, 共存物种间的生态位分化等确定性因素占主导地
16、位; 而另一种观点则认为扩散和随机作用是主要决定因子。关于群落构建的确定性和非确定性因素, 达尔文在其巨著物种起源中早有所提及。他认为看似偶然生长在一起的群落物种, 其背后有着深刻的必然性。而对确定性因素和随机作用在群落构建中的地位较为系统的讨论, 可以追溯到20世纪初的群落超有机体论(super-organism concept) (Clements, 1916; Tansley, 1935)和个体论(individualistic concept)(Gleason, 1926)的争论。以Clements为代表的群落有机体学派认为, 群落构建是确定性过程, 群落之间有着可分辨的边界, 群落在受干扰后能够逐渐演变到原来的状态, 即群落演替; 在群落组分种的相互作用下, 演替是从一个方向有规律地向另一个方向变化, 演替的最后阶段是稳定的单元顶极(monoclimax)(Clements, 1916)或多元顶极(polyclimax)(Tansley, 1935)。对此,
