Fung Tak, Villain Laura, Chisholm Ryan A
National University of Singapore, Department of Biological Sciences, 14 Science Drive 4, 117543 Singapore.
Institut National des Sciences Appliquées de Lyon, 20 Avenue Albert Einstein, Villeurbanne cedex, 69621 Lyon, France.
J Theor Biol. 2015 Dec 7;386:147-58. doi: 10.1016/j.jtbi.2015.09.011. Epub 2015 Sep 25.
The evenness of an ecological community affects ecosystem structure, functioning and stability, and has implications for biodiversity conservation. In uneven communities, most species are rare while a few dominant species drive ecosystem-level properties. In even communities, dominance is lower, with possibly many species playing key ecological roles. The dominance aspect of evenness can be measured as a decreasing function of the proportion of species required to make up a fixed fraction (e.g., half) of individuals in a community. Here we sought general rules about dominance in ecological communities by linking dominance mathematically to the parameters of common theoretical species-abundance distributions (SADs). We found that if a community's SAD was log-series or lognormal, then dominance was almost inevitably high, with fewer than 40% of species required to account for 90% of all individuals. Dominance for communities with an exponential SAD was lower but still typically high, with fewer than 40% of species required to account for 70% of all individuals. In contrast, communities with a gamma SAD only exhibited high dominance when the average species abundance was below a threshold of approximately 100. Furthermore, we showed that exact values of dominance were highly scale-dependent, exhibiting non-linear trends with changing average species abundance. We also applied our formulae to SADs derived from a mechanistic community model to demonstrate how dominance can increase with environmental variance. Overall, our study provides a rigorous basis for theoretical explorations of the dynamics of dominance in ecological communities, and how this affects ecosystem functioning and stability.
生态群落的均匀度会影响生态系统的结构、功能和稳定性，对生物多样性保护也具有重要意义。在不均匀的群落中，大多数物种较为稀少，而少数优势物种决定着生态系统层面的特征。在均匀的群落中，优势度较低，可能有许多物种发挥着关键的生态作用。均匀度的优势度方面可以通过作为群落中构成固定比例（例如一半）个体所需物种比例的递减函数来衡量。在这里，我们通过将优势度与常见理论物种-多度分布（SADs）的参数进行数学关联，来探寻生态群落中优势度的一般规律。我们发现，如果一个群落的SAD是对数级数或对数正态分布，那么优势度几乎不可避免地较高，不到40%的物种就能占到所有个体的90%。具有指数SAD的群落的优势度较低，但通常仍然较高，不到40%的物种就能占到所有个体的70%。相比之下，具有伽马SAD的群落只有在平均物种多度低于约100的阈值时才表现出高优势度。此外，我们还表明，优势度的精确值高度依赖尺度，随着平均物种多度的变化呈现非线性趋势。我们还将我们的公式应用于从一个机械群落模型推导出来的SAD，以证明优势度如何随环境方差增加。总体而言，我们的研究为生态群落中优势度动态的理论探索以及这如何影响生态系统功能和稳定性提供了一个严谨的基础。
