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. 许多短命物种会在环境条件适宜的短暂季节窗口期内完成其生活史。面对气候变暖，这类物种可通过空间上追踪其季节气候生态位（seasonal climate niche）的迁徙，或是通过年内物候（phenology）转变及时追踪有利环境条件来实现存续。为描述加利福尼亚州一年生短命植物轮生粟米草（Mollugo verticillata）的季节气候生态位，我们利用标本馆标本数据与历史气候记录，估算了每份标本采集地点、月份及年份对应的环境条件。
2. 我们基于这些数据，在最大熵模型（MaxEnt）框架下构建了该物种的季节物种分布模型（species distribution model, SDM），以刻画其在加利福尼亚州全季节、全地点的总气候空间内的气候生态位。该模型可实现精细化的时空生境适宜性预测，同时指明该物种的可观测地点与时间。
3. 我们将该模型的预测结果与基于年平均气候数据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，轮生粟米草在加利福尼亚州的分布局限于温暖环境。但季节物种分布模型还可通过绘制全州每个月的气候适宜性来预测物候：轮生粟米草仅分布于温暖月份，其季节气候生态位在年内会随空间发生迁移。
4. 我们借助该季节物种分布模型，针对三种变暖情景，绘制了年内各月的预测未来物种分布。模型预测，在多数区域，该物种的分布范围将扩张，且年内出现时间会提前；在最温暖的区域，暖季的生境适宜性会下降，这可能导致其物候呈现双峰模式，且仲夏存在一段空窗期。
5. 总结——我们基于标本馆记录与逐月气象数据开发了一种全新的物种分布模型，该模型不仅可预测短命物种的分布地点，还可预测其在对应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。