Supplement 1. Data and R code for analyzing extinction times of experimental Daphnia populations.

File List data.csv - Table of raw data<br> DaphExt.r - R code for performing analysis Description The file data.csv is a comma separated ASCII file containing extinction times for 281 populations of <i>Daphnia magna</i> under three levels of environmental variation. The first line is a header containing variable names. The variable treatment takes values "low", "medium", or "high" referring to the experimental treatment. The variables treatment2 and treatment3 are re-coded versions of treatment provided for convenience. The variable treatment2 assigns the level "A" to subjects in the "low" experimental treatment, assigns "B" to subjects in the "medium" experimental treatment, and assigns "C" to subjects in the "high" experimental treatment. The variable treatment3 pools subjects in the "low" and "medium" treatments, assigning them the level "A", while subjects in the "high" experimental treatment are assigned "C", as before. The variable id is a unique identifier for each population. The variable ext is a censoring variable, taking the value "1" if the population went extinct during the course of the experiment and "0" otherwise. The variable dur reports the duration of population observation, the time-to-extinction in the case of populations going extinct and the duration of the experiment otherwise. The file DaphExt.r contains R code for performing the Cox proportional hazards regression, estimating the survival distribution using the Kaplan-Meier estimator, and reproducing figures from the text. In addition to the basic R environment, this code depends on functions in the package survival which can be obtained along with the basic R environment from the Comprehensive R Archive Network (CRAN) found at www.r-project.org.

文件列表：data.csv - 原始数据表；DaphExt.r - 用于执行分析的R代码

描述：data.csv为逗号分隔的ASCII文件，包含3种环境变异水平下281个大型溞（Daphnia magna）种群的灭绝时间。文件首行为包含变量名的表头。变量treatment的取值为"low"、"medium"或"high"，分别对应实验处理的低、中、高三个水平。变量treatment2与treatment3是为便于使用而对treatment进行的重新编码版本：其中treatment2将"low"处理组的种群赋值为"A"，"medium"组赋值为"B"，"high"组赋值为"C"；treatment3将"low"与"medium"处理组合并，赋值为"A"，"high"组仍赋值为"C"。变量id为每个种群的唯一标识符。变量ext为删失变量，若种群在实验过程中发生灭绝则取值为"1"，否则为"0"。变量dur用于报告种群观测时长：若种群灭绝则记录为灭绝时间，若未灭绝则记录为实验总时长。

文件DaphExt.r包含用于执行Cox比例风险回归、采用Kaplan-Meier估计器拟合生存分布，以及复现原文中图表的R代码。除基础R环境外，该代码依赖survival包中的函数，该包可与基础R环境一同从综合R档案网络（Comprehensive R Archive Network，CRAN，官网地址为www.r-project.org）获取。