Schwartz M W, Brigham C A, Hoeksema J D, Lyons K G, Mills M H, van Mantgem P J
Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA e-mail:
Oecologia. 2000 Feb;122(3):297-305. doi: 10.1007/s004420050035.
We evaluate the empirical and theoretical support for the hypothesis that a large proportion of native species richness is required to maximize ecosystem stability and sustain function. This assessment is important for conservation strategies because sustenance of ecosystem functions has been used as an argument for the conservation of species. If ecosystem functions are sustained at relatively low species richness, then arguing for the conservation of ecosystem function, no matter how important in its own right, does not strongly argue for the conservation of species. Additionally, for this to be a strong conservation argument the link between species diversity and ecosystem functions of value to the human community must be clear. We review the empirical literature to quantify the support for two hypotheses: (1) species richness is positively correlated with ecosystem function, and (2) ecosystem functions do not saturate at low species richness relative to the observed or experimental diversity. Few empirical studies demonstrate improved function at high levels of species richness. Second, we analyze recent theoretical models in order to estimate the level of species richness required to maintain ecosystem function. Again we find that, within a single trophic level, most mathematical models predict saturation of ecosystem function at a low proportion of local species richness. We also analyze a theoretical model linking species number to ecosystem stability. This model predicts that species richness beyond the first few species does not typically increase ecosystem stability. One reason that high species richness may not contribute significantly to function or stability is that most communities are characterized by strong dominance such that a few species provide the vast majority of the community biomass. Rapid turnover of species may rescue the concept that diversity leads to maximum function and stability. The role of turnover in ecosystem function and stability has not been investigated. Despite the recent rush to embrace the linkage between biodiversity and ecosystem function, we find little support for the hypothesis that there is a strong dependence of ecosystem function on the full complement of diversity within sites. Given this observation, the conservation community should take a cautious view of endorsing this linkage as a model to promote conservation goals.
我们评估了一种假设的实证和理论依据，该假设认为需要大量的本地物种丰富度才能使生态系统稳定性最大化并维持其功能。这种评估对于保护策略很重要，因为生态系统功能的维持一直被用作保护物种的论据。如果生态系统功能在相对较低的物种丰富度下就能维持，那么以保护生态系统功能为由（无论其本身多么重要），并不能有力地支持保护物种。此外，要使这成为一个有力的保护论据，物种多样性与对人类社会有价值的生态系统功能之间的联系必须清晰。我们回顾实证文献以量化对两个假设的支持：（1）物种丰富度与生态系统功能呈正相关，以及（2）相对于观察到的或实验性的多样性，生态系统功能在低物种丰富度时不会饱和。很少有实证研究表明在高物种丰富度水平下功能会得到改善。其次，我们分析了近期的理论模型，以估计维持生态系统功能所需的物种丰富度水平。我们再次发现，在单一营养级内，大多数数学模型预测生态系统功能在当地物种丰富度的低比例时就会饱和。我们还分析了一个将物种数量与生态系统稳定性联系起来的理论模型。该模型预测，除了最初的几个物种之外，物种丰富度通常不会增加生态系统稳定性。高物种丰富度可能对功能或稳定性贡献不大的一个原因是，大多数群落的特征是优势度很强，以至于少数物种提供了群落生物量的绝大部分。物种的快速更替可能会挽救多样性导致最大功能和稳定性这一概念。物种更替在生态系统功能和稳定性中的作用尚未得到研究。尽管最近人们急于接受生物多样性与生态系统功能之间的联系，但我们发现几乎没有证据支持生态系统功能强烈依赖于地点内多样性的完整组合这一假设。基于这一观察结果，保护界在将这种联系作为促进保护目标的模型予以认可时应持谨慎态度。
