Data from: Geo-climatic factors drive diatom community distribution in tropical South American freshwaters

1.Patterns that maintain and generate biodiversity of macro-organisms in the Neotropics are widely discussed in the scientific literature, yet the spatial ecology of microorganisms is largely unknown. The unique character of the tropical Andes and adjacent Amazon lowlands generates a wide gradient of environmental conditions to advance our understanding of what drives community assembly and diversity processes.

2.We analyzed the distribution patterns of benthic diatoms (unicellular siliceous algae) as a model group of microbial passive dispersers, including predictors that describe limnological and geo-climatic gradients for a total of 113 waterbodies (0–28ºS and 58–80ºW), including lakes and streams. Complementary multivariate statistical analyses were performed to correlate i) community composition, and ii) diatom species richness with environmental and spatial factors to infer niche-based and dispersal-based assembly processes, respectively.

3.Results showed that two gradients structured both diatom assemblages and waterbodies, namely climate and landscape configuration. Variance partitioning revealed that broad-scale spatial variables (distance-based Moran's Eigenvectors) outperformed the two environmental components (limnological and geo-climatic), suggesting dispersal-assembled communities. However, diatom assemblages were structured by geo-climatic (regional) factors in certain lakes in the northern and central Andes, although their effects were partially manifested via local variables after the geographical distances were factored out. In a similar way, climatic and topographic structuring homogenized lake and stream communities within ecoregions, as indicated by the strong overlap between the two community types and the weak correlation between biota and limnological variables. Notably, a significant increase in diatom species richness was related to increased water connectivity, interpreted to indicate that a decrease in the remoteness of the system increase species number.

4.Synthesis. We emphasize the strength of macroecological gradients (landscape configuration and climatic factors) in affecting both diatom diversity and community composition in the South American tropics. In this context, our results and the commonalities of ecoregion patterning with groups of macroorganisms (vegetation), suggest the need to integrate microbial ecology into a macroecology framework to unravel mechanisms behind diversity gradients.

1. 新热带区（Neotropics）维持并驱动大型生物（macro-organisms）生物多样性的模式，已在科学文献中得到广泛探讨，但微生物的空间生态学（spatial ecology）在很大程度上仍未被充分探明。热带安第斯山脉及其毗邻的亚马孙低地所独具的特质，造就了跨度广阔的环境梯度，为我们深入理解驱动群落组装（community assembly）与多样性过程的核心因素提供了研究契机。
2. 本研究以底栖硅藻（benthic diatoms，即单细胞硅质藻类）作为微生物被动扩散类群的模式类群，分析其分布模式；研究共纳入113个水体（地理范围为南纬0°–28°、西经58°–80°，涵盖湖泊与溪流），并选取描述湖沼学与地理气候梯度的预测变量。通过互补性多元统计分析，我们分别将i）群落组成、ii）硅藻物种丰富度与环境及空间因子进行关联，以此推断基于生态位的与基于扩散的群落组装过程。
3. 研究结果显示，气候与景观配置两大梯度共同塑造了硅藻群落与水体的结构。方差分解（variance partitioning）结果表明，大尺度空间变量（即基于距离的莫兰特征向量（distance-based Moran's Eigenvectors））优于两类环境因子（湖沼学与地理气候因子），提示群落以扩散驱动组装。不过，安第斯山脉北部与中部的部分湖泊中，硅藻群落的结构由地理气候（区域）因子主导；但在剔除地理距离的影响后，这类因子的效应可部分通过局地变量体现。类似地，气候与地形塑造作用使得生态区（ecoregions）内的湖泊与溪流群落趋于同质化，这一点可通过两类群落类型间的高度重叠，以及生物群落（biota）与湖沼学变量间的弱相关性得到佐证。值得注意的是，硅藻物种丰富度的显著提升与水体连通性（water connectivity）的增强呈正相关，这一结果表明系统的偏远程度越低，物种数量越多。
4. 研究总结：我们着重指出，大生态梯度（景观配置与气候因子）对南美热带地区的硅藻多样性与群落组成均存在显著影响。在此背景下，本研究结果以及生态区格局与大型生物（植被）类群的共性特征，提示我们需将微生物生态学（microbial ecology）纳入大生态学（macroecology）框架，以阐明多样性梯度背后的核心机制。