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首页> 外文期刊>Freshwater Biology >The Goldilocks effect: intermittent streams sustain more plant species than those with perennial or ephemeral flow.
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The Goldilocks effect: intermittent streams sustain more plant species than those with perennial or ephemeral flow.

机译：金发姑娘效应：间歇性河流比常年性或短暂性河流的植物种类多。

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Drylands worldwide are typified by extreme variability in hydrologic processes, which structures riparian communities at various temporal and spatial scales. One key question is how underlying differences in hydrology over the length of interrupted perennial rivers influence spatial and temporal patterns in species richness and species composition. We examined effects of differences in dry season hydrology on species richness, composition and cover of herbaceous plant communities in the streamside zone (the zone influenced directly by low flows in the channel). Data were collected at ephemeral, intermittent and perennial flow reaches on three rivers of the desert Southwest (Arizona, U.S.A.): Lower Cienega Creek, Hassayampa River and Lower San Pedro River. Patterns of species richness varied with temporal scale of analysis, that is between single-year and multi-year time frames. At the annual timescale, quadrat species richness (m-2) and herbaceous cover were higher at sites with perennial flow than at either intermittent or ephemeral sites. In contrast to this single-year pattern, the highest long-term richness occurred at intermittent sites. Quadrat species richness, total species richness at a site (per 18 1-m2 plots) and cover were more variable year to year at non-perennial sites than at perennial flow sites. On two of the three rivers, ephemeral sites had the highest inter-annual compositional variance, while the perennial sites had the lowest. Compositional differences between the hydrologic site types were dominated by species turnover, not nestedness. The perennial sites had more wetland and perennial species than the other two site types. The intermittent sites had more annual species than did the other two types. High long-term species richness and distinct species composition of intermittent sites are probably sustained by pronounced temporal variability in environmental conditions (i.e. frequent and persistent flow events, and dry periods). Plants at these sites take advantage of greater moisture than those at ephemeral sites and also experience less competition from resident species than those at perennial sites. Conservation of desert riparian diversity depends upon the protection of consistently wet conditions at perennial flow sites, as well as the maintenance of the processes that cause fluctuations in environmental conditions at non-perennial sites.Digital Object Identifier http://dx.doi.org/10.1111/j.1365-2427.2011.02714.x
机译：世界各地的旱地以水文过程的极端可变性为代表，该过程在不同的时空尺度上构成了河岸群落。一个关键问题是多年生中断河流的长度在水文方面的根本差异如何影响物种丰富度和物种组成的时空格局。我们研究了旱季水文差异对河岸区（河道中低流量直接影响的区域）草本植物群落物种丰富度，组成和覆盖度的影响。在西南沙漠（美国亚利桑那州）的三条河上以短暂，断断续续和多年生的流量采集数据：下西埃涅加河，哈塞桑帕河和下圣佩德罗河。物种丰富度的模式随分析的时间尺度而变化，即在一年和多年的时间框架之间。在一年的时间尺度上，多年生植物流域的四倍体物种丰富度（m -2 ）和草本覆盖率高于间歇性或短暂性场所。与这种单一年份模式相反，最高的长期丰富度发生在间歇性地点。与多年生流域相比，非多年生植物种群的Quadrat物种丰富度，一个场所的总物种丰富度（每18 1-m 2 个地块）和覆盖率逐年变化。在这三条河流中的两条上，短暂地点的年际组成变化最大，而多年生地点的最低。水文位点类型之间的成分差异主要由物种更新而不是嵌套引起。多年生地点比其他两个地点类型具有更多的湿地和多年生物种。与其他两种类型相比，间歇性地点的年度物种更多。在环境条件下（即频繁和持续的流动事件以及干旱时期），明显的时间变化可能会维持较高的长期物种丰富度和间歇位置的独特物种组成。与多年生植物相比，这些植物比短暂植物具有更多的水分，并且与本地物种的竞争也更少。荒漠河岸多样性的保护取决于多年生流域持续稳定的湿润条件以及非多年生站点维持引起环境条件波动的过程。数字对象标识符http://dx.doi.org /10.1111/j.1365-2427.2011.02714.x

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