Laboratory of Ecology and Physiology of Phytoplankton, Department of Plant Biology, State University of Rio de Janeiro, Rua São Francisco Xavier 524, PHLC, Sala 511a, 20550-900 Rio de Janeiro, Brazil; University of Helsinki, Department of Geosciences and Geography, PO Box 64, FI-00014 Helsinki, Finland.
Laboratory of Phycology, National Museum, Federal University of Rio de Janeiro, 20940-040 Rio de Janeiro, Brazil.
Sci Total Environ. 2020 Feb 10;703:135519. doi: 10.1016/j.scitotenv.2019.135519. Epub 2019 Nov 14.
Environmental heterogeneity (EH) in space and time promotes niche-partition, which leads to high variation in biological communities, such as in algae. In streams, EH is highly related to the intensity of the water flow and may lead to community variation mainly during the low flow conditions. Despite the wide knowledge on the responses of phytoplankton communities to EH in lentic and semi-lentic systems, studies of riverine phytoplankton community variation are still scarce. Here, we first investigated the relationship between phytoplankton community variation and EH in different courses of the river and between seasons. We expected that under low or intermediate flow conditions, there is a positive correlation between community variation and EH. Alternatively, we did not expect any relationship between EH and community variation under high flow condition because stronger downstream transport would mask environmental filtering. We sampled nine sites monthly (May 2012 to April 2013) in a tropical river of Brazilian Southeast. We calculated EH from abiotic data whereas for community variation, here community distinctiveness (CD), we used Sorensen (CD) and Bray-Curtis (CD) dissimilarities. Differences in EH, CD and CD were tested at between-season and among-course levels. We found lower distinctiveness during the dry season when EH was the highest. Contrastingly, phytoplankton CD was the highest even when EH was low during the wet season. We found that this pattern raised from the increasing in individuals dispersal during the wet season, promoting mass effects. Finally, our results thus reject the first hypothesis and show a negative relationship between EH and distinctiveness. However, results support our alternative hypothesis and show that during the wet season, distinctiveness is not driven by EH. These results provide new insights into how EH drives community variation, being useful for both basic research about riverine algal communities and biomonitoring programs using phytoplankton communities as bioindicators.
环境异质性（EH）在时间和空间上促进了小生境的分化，从而导致生物群落的高度变异，如藻类。在溪流中，EH 与水流强度密切相关，可能主要在低流量条件下导致群落变异。尽管人们对淡水和半淡水系统中浮游植物群落对 EH 的响应有广泛的了解，但河流浮游植物群落变异的研究仍然很少。在这里，我们首先研究了不同河道和季节浮游植物群落变异与 EH 之间的关系。我们预计，在低或中等流量条件下，群落变异与 EH 呈正相关。或者，我们预计在高流量条件下 EH 与群落变异之间没有关系，因为更强的下游输送会掩盖环境过滤。我们于 2012 年 5 月至 2013 年 4 月每月在巴西东南部的一条热带河流中采集了九个地点的样本。我们从生物物理数据中计算 EH，而对于群落变异，我们使用 Sorensen（CD）和 Bray-Curtis（CD）差异来表示群落独特性（CD）。在季节间和河道间水平上测试了 EH、CD 和 CD 的差异。我们发现，在旱季 EH 最高时，独特性较低。相反，即使在雨季 EH 较低时，浮游植物的 CD 最高。我们发现，这种模式是由于雨季个体扩散的增加而产生的，促进了质量效应。最后，我们的结果因此否定了第一个假设，并显示 EH 与独特性之间呈负相关。然而，结果支持我们的替代假设，并表明在雨季，独特性不受 EH 的驱动。这些结果为 EH 如何驱动群落变异提供了新的见解，这对于河流藻类群落的基础研究和使用浮游植物群落作为生物指标的生物监测计划都是有用的。
