Matthews William J, Marsh-Matthews Edie
Ecology. 2016 Mar;97(3):706-19.
Previous theoretical models and empirical studies suggested that communities can exist in a "stochastic" or "loose" equilibrium, diverging transiently but eventually returning toward earlier or average structure, in what we call here the "loose equilibrium concept" (LEC). We sampled the fish communities at 12 local stream reaches spaced broadly throughout a relatively undisturbed watershed in the Ozark Mountains of northern Arkansas, USA, in 11 surveys from 1972 to 2012 at a scale of decades, and at a subset of five of these local sites in a total of 16 surveys, allowing tests of the LEC at different spatial and temporal scales. Multivariate analyses of the dynamics of communities over the 40-year period provided support for the LEC at both "global" and "local" scales within the watershed. At the broadest spatial scale, core species numerically dominated the community, and most common species remained so across all decades. In spite of two extraordinary floods, and interannual variation in abundance of some species, the 12-site and five-site global communities and eight of 12 local communities repeatedly returned toward average positions in multivariate space. Trajectories of the global and local fish communities varied relative to model hypothetical trajectories that were based on gradual vs. saltatory changes, and prevalence of returns toward average community structure. Beta diversity among sites was variable across time, but beta partitioning consistently showed that pure spatial turnover dominated over nestedness, because many common species were consistently distributed either upstream or downstream. This study suggests that vertebrate communities in relatively undisturbed environments may display dynamics consistent with the LEC. The LEC, combined with quantification of community trajectory patterns, can help to clarify whether systems are moving about within ranges of conditions that reflect expected noise, or, conversely, have moved so far out of previous bounds, as a result of climate change or human intervention, that they are permanently changed or "novel."
先前的理论模型和实证研究表明，群落可以处于一种“随机”或“松散”的平衡状态，即暂时偏离但最终会回归到早期或平均结构，我们在此将其称为“松散平衡概念”（LEC）。我们在美国阿肯色州北部奥扎克山脉一个相对未受干扰的流域内，对12个当地溪流河段的鱼类群落进行了采样。在1972年至2012年期间，以数十年为尺度进行了11次调查，并在其中5个当地站点的子集中进行了总共16次调查，从而能够在不同的空间和时间尺度上对LEC进行测试。对40年期间群落动态的多变量分析为流域内“全球”和“局部”尺度的LEC提供了支持。在最广泛的空间尺度上，核心物种在数量上主导着群落，并且大多数常见物种在所有几十年中都保持这种状态。尽管发生了两次特大洪水以及某些物种数量的年际变化，但12个站点和5个站点的全球群落以及12个当地群落中的8个在多变量空间中反复回归到平均位置。全球和局部鱼类群落的轨迹相对于基于渐变与跃变变化以及回归到平均群落结构的普遍性的模型假设轨迹有所不同。站点间的β多样性随时间变化，但β划分始终表明，纯粹的空间周转率比嵌套性占主导，因为许多常见物种始终分布在上游或下游。这项研究表明，在相对未受干扰的环境中的脊椎动物群落可能表现出与LEC一致的动态。LEC与群落轨迹模式的量化相结合，可以帮助阐明系统是在反映预期噪声的条件范围内波动，还是相反，由于气候变化或人类干预而已经偏离了先前的界限，以至于它们被永久改变或“全新”。
