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）内维持和驱动大型生物生物多样性的模式在科学文献中已被广泛探讨，但微生物的空间生态学在很大程度上仍未被探明。热带安第斯山脉（tropical Andes）及其毗邻的亚马逊低地（Amazon lowlands）拥有独特的环境特征，形成了跨度极大的环境梯度，为我们深入理解驱动群落组装与多样性形成过程的机制提供了研究契机。
2. 本研究以底栖硅藻（benthic diatoms，单细胞硅质藻类（unicellular siliceous algae））作为微生物被动扩散类群的模式生物，分析其分布模式；研究共纳入113个水体（南纬0°~28°、西经58°~80°，涵盖湖泊与溪流），并选取描述湖沼学（limnological）与地理气候（geo-climatic）梯度的预测变量。随后通过补充性多元统计分析，分别将i）群落组成、ii）硅藻物种丰富度与环境及空间因子相关联，以此分别推断基于生态位的群落组装过程与基于扩散的群落组装过程。
3. 研究结果显示，气候与景观配置两类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（基于距离的莫兰特征向量（distance-based Moran's Eigenvectors））相较于两类环境因子（湖沼学与地理气候因子）表现更优，提示该区域硅藻群落为扩散组装型群落。不过在安第斯山脉北部与中部的部分湖泊中，硅藻群落的组装受地理气候（区域）因子调控，但在剔除地理距离的影响后，其效应可通过局地变量部分体现。类似地，气候与地形因子的调控作用使得生态区（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与湖沼学变量间的弱相关性得到印证。值得注意的是，硅藻物种丰富度随水体连通性提升而显著增加，这一结果表明生境偏远程度的降低会提升物种数量。
4. 研究总结：本研究强调，宏生态学（macroecology）梯度（即景观配置与气候因子）对南美热带地区硅藻多样性与群落组成具有显著调控作用。在此背景下，结合本研究结果以及大型生物类群（如植被）的生态区分布模式共性，我们认为有必要将微生物生态学纳入宏生态学研究框架，以阐明多样性梯度背后的形成机制。