Data from: The seasonal climate niche predicts phenology and distribution of an ephemeral annual plant, Mollugo verticillata

1.Many short-lived species complete their life cycles during brief seasonal windows of favorable environmental conditions. Such species may persist in the face of climate warming by migration to track their seasonal climate niche in space and/or by phenological shifts to track favorable conditions in time within the year. To describe the seasonal climate niche of the short-lived annual Mollugo verticillata in California, we used data from herbarium specimens and historic climate records to estimate environmental conditions at the location, month and year of each collection. 2.We used these data in a MaxEnt framework to construct a seasonal species distribution model (SDM) of the species’ climate niche within the total climate space available across all seasons and locations in California. The model provides fine-scale spatial and temporal predictions of habitat suitability, predicting both where and when the species should be observed. 3.We compared the predictions of the model to those from a conventional SDM based on mean annual climate data. Both models showed that M. verticillata is limited to warm environments within California. However, the seasonal SDM also predicted phenology by mapping climate suitability across the state for each month of the year. Mollugo verticillata is limited to warm months, and its seasonal climate niche shifts in space across California in the course of the year. 4.We used the seasonal SDM to map the predicted future species distribution for each month of the year under three warming scenarios. The species is predicted to expand its range and occur earlier in the year in most locations; in the warmest locations seasonal suitability is predicted to decline in the warmest months, which may result in bimodal phenology with a mid-summer gap. 5.Synthesis - We developed a novel species distribution model using herbarium records and monthly weather data, which predicts not only where a short-lived species should be found, but when during the year it is predicted to occur in those areas. This model can be used to predict how climate change will affect the species distribution in space as well as seasonal phenology across the landscape.1. 短命物种多在短暂的有利环境季节窗口期内完成生活史。面对气候变暖，此类物种可通过空间上追踪其季节气候生态位（seasonal climate niche）的迁移，或年内时间上追踪有利环境的物候（phenology）偏移来维持种群存续。为阐明加州一年生短命植物轮叶粟米草（Mollugo verticillata）的季节气候生态位，本研究利用标本馆标本（herbarium specimens）与历史气候数据，估算每份标本采集地、采集月份及采集年份对应的环境条件。 2. 本研究基于最大熵（MaxEnt）模型框架，利用上述数据构建了加州全季节、全区域气候空间内该物种气候生态位的季节型物种分布模型（species distribution model, SDM）。该模型可输出精细时空尺度的生境适宜性预测结果，同时指明该物种的适宜分布区域与观测窗口期。 3. 本研究将该模型的预测结果与基于年平均气候数据构建的传统物种分布模型的预测结果进行了对比。两类模型均显示，轮叶粟米草在加州的分布局限于温暖生境。但季节型SDM还可通过绘制加州全年各月份的气候适宜性分布来预测物候：轮叶粟米草仅在温暖月份适宜生存，其季节气候生态位会随年内时间在加州空间范围内发生偏移。 4. 本研究利用季节型SDM，绘制了三种气候变暖情景下加州全年各月份的未来物种分布预测结果。预测显示，多数区域内该物种的分布范围将扩张，且年内出现时间提前；在最温暖的区域，其生境适宜性在最热月份会出现下降，这可能导致物候呈现双峰模式，且仲夏存在一段适宜性空白期。 5. 总结——本研究利用标本馆记录与逐月气象数据，构建了一种新型物种分布模型，该模型不仅可预测短命物种的分布区域，还可预测该物种在这些区域内的年内出现时间。此模型可用于预测气候变化如何从空间维度影响物种分布，以及如何从景观尺度影响季节物候。