Department of Biology, University of Texas at Arlington, Box 19498, Arlington, TX 76019-0498, USA.
Microb Ecol. 2011 Aug;62(2):414-24. doi: 10.1007/s00248-011-9879-7. Epub 2011 May 27.
The century-long research on succession has bestowed us with a number of theories, but little agreement on what causes species replacements through time. The majority of studies has explored the temporal trends of individual species in plant and much less so in microbial communities, arguing that interspecific interactions, especially competition, play a key role in community organization throughout succession. In this experimental investigation of periphytic succession in re-circulating laboratory streams, we examined the density and the relative abundance of diatoms and soft algae for 35 days across gradients of low to high nutrient supply (nitrogen + phosphorus) and low to intermediate current velocity (10 vs. 30 cm·s(-1)). All algal species were classified into trophic groups and morphological guilds, both of which responded more strongly to nutrient than current velocity manipulations, as shown by regression analyses. We concluded that within the manipulated environmental ranges: (1) Succession was a gradient of stress tolerance, driven primarily by nutrient supply and secondarily, by current velocity. Nutrient supply had a qualitative effect in determining whether the contribution of species tolerant vs. sensitive to nutrient limitation would increase through time, while current velocity had a quantitative influence and affected only the rate of this increase. (2) The mechanism of algal succession at a functional level was a neutral coexistence, whereby the tolerant low profile guild maintained high density when overgrown by sensitive species, while sensitive species, constituting mostly the motile and high profile guilds, were neither facilitated nor inhibited by tolerant species but controlled by the environment. It is suggested that the mechanism of succession may depend on the level of biological organization with interspecific interactions giving way to neutral coexistence along the hierarchy from species to functional groups. Considering that the functional makeup is strictly environmentally defined, while species composition reflects local and regional species pools that may exhibit substantial geographic variability, succession is deterministic at a functional level but stochastic at a species level.
一个世纪以来，对演替的研究为我们提供了许多理论，但对于是什么导致物种随时间更替仍存在分歧。大多数研究都探讨了植物种个体随时间的趋势，而对微生物群落的研究则较少，这表明种间相互作用，特别是竞争，在演替过程中对群落组织起着关键作用。在这项关于循环实验室溪流周丛生物演替的实验研究中，我们在低到高养分供应（氮+磷）和低到中等流速（10 与 30 cm·s(-1))梯度下，对硅藻和软藻的密度和相对丰度进行了 35 天的研究。所有藻类物种都被分为营养组和形态群，回归分析表明，这两组对养分的响应都比对流速的响应更为强烈。我们的结论是，在所操纵的环境范围内：（1）演替是一种胁迫耐受性的梯度，主要由养分供应驱动，其次由流速驱动。养分供应在决定对养分限制有耐受性和敏感性的物种的贡献是否会随着时间的推移而增加方面具有定性作用，而流速具有定量影响，仅影响这种增加的速度。（2）在功能水平上，藻类演替的机制是中性共存，即耐受低形态群在被敏感物种过度生长时保持高密度，而敏感物种主要构成运动和高形态群，既不受耐受物种的促进也不受抑制，但受环境控制。因此，演替的机制可能取决于生物组织的水平，随着种间相互作用沿着从物种到功能群的层次结构让位于中性共存。考虑到功能组成严格由环境定义，而物种组成反映了可能具有显著地理变异性的局部和区域物种库，演替在功能水平上是确定性的，而在物种水平上是随机的。
