Community size affects the signals of niche selection and ecological drift on beta diversity in stream organisms: data and script

This is a unique dataset on insect communities sampled identically in a total of 200 streams in climatically highly different regions (100 in Brazil and 100 in Finland). The sampling design included 5 streams (communities) per watershed and provided us replicates of metacommunities (watersheds). Data also include information on in-stream variables (such as current velocity (m/s), depth (cm), stream width (cm), % of sand (0.25-2 mm), gravel (2-16 mm), pebble (16-64 mm), cobble (64-256 mm), and boulder (256-1024 mm), % of canopy cover by riparian vegetation, pH, conductivity, total nitrogen, and total phosphorus) and catchment level variables (such as average slope, % of native forest cover, pasture, agriculture, planted forests, urban areas, mining, water bodies, bare soil, secondary forest cover, and mixed land uses). In addition to the dataset, here we also provide and R code used to investigate the relationship between beta diversity and community size. This code calculates 4 types of beta-diversity metric for each of 100 watersheds (5 streams) in Brazil and Finland. Beta diversity: Sorensen and Bray-Curtis dissimilarity between all pairs. Beta deviation from null models: Raup-Crick (vegan version) and Bray-Curtis beta-deviation (based on the scripts by Chris Catano and Jonathan Myers). These beta diversity metrics are modelled against community size, environmental heterogeneity and spatial extent.本数据集为一套独特的昆虫群落标准化采样数据集，在气候差异极大的两个区域共计200条溪流中完成采样：其中巴西境内100条，芬兰境内100条。本次采样设计以每个集水区（watershed）设置5条溪流（对应5个昆虫群落）的方案开展，从而获得了集合群落（metacommunities）的重复样本。数据集同时包含溪流原位环境变量与集水区尺度环境变量两类信息：其中溪流原位环境变量涵盖水流速度（单位：m/s）、水深（cm）、溪流宽度（cm）、沙粒（0.25-2 mm）占比、砾石（2-16 mm）占比、卵石（16-64 mm）占比、大砾石（64-256 mm）占比、巨砾（256-1024 mm）占比、河岸植被冠层覆盖率、pH值、电导率、总氮及总磷；集水区尺度环境变量则包括平均坡度、原生林覆盖率、牧场占比、农田占比、人工林占比、城区占比、采矿区占比、水体占比、裸地占比、次生林覆盖率以及混合土地利用类型占比。 除本数据集外，本次还附带了用于探究β多样性（beta diversity）与群落规模之间关系的R代码。该代码可针对巴西与芬兰各100个集水区（对应5条溪流）分别计算4类β多样性度量指标：其中β多样性指标为所有样本对之间的索伦森相异指数（Sorensen dissimilarity）与布莱-柯蒂斯相异指数（Bray-Curtis dissimilarity）；基于零模型（null models）的β偏差值指标则包括劳普-克里克指数（Raup-Crick，vegan包版本）与布莱-柯蒂斯β偏差值（基于Chris Catano与Jonathan Myers编写的脚本）。随后将上述β多样性度量指标与群落规模、环境异质性及空间范围开展建模分析。