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. 许多短命物种会在短暂的适宜环境季节窗口期内完成其生活史。这类物种可通过两种方式应对气候变暖：一是通过空间迁移追踪其季节性气候生态位，二是通过物候转变在年内的时间维度上追踪适宜环境条件。为描述加州短命一年生植物轮叶粟米草（Mollugo verticillata）的季节性气候生态位，本研究采用标本馆标本数据与历史气候记录，估算每份标本采集时的地点、月份与年份对应的环境条件。
2. 我们采用该数据结合最大熵（MaxEnt）模型框架，构建了该物种的季节性气候生态位物种分布模型（Species Distribution Model, SDM），模型覆盖加州所有季节与地点的潜在气候空间范围。该模型可实现精细尺度的空间与时间维度栖息地适宜性预测，同时精准预测该物种的适宜观测地点与时间。
3. 我们将该季节性SDM的预测结果与基于年平均气候数据的传统SDM预测结果进行对比。两类模型均显示，轮叶粟米草在加州仅分布于温暖环境中。但季节性SDM还可通过绘制加州全年各月的气候适宜性分布来预测物候特征：该物种仅在温暖月份适宜生存，其季节性气候生态位在年内会随加州的空间位置发生动态偏移。
4. 我们利用该季节性SDM，针对三种变暖情景，绘制了该物种全年各月的未来潜在分布格局。预测显示，在多数区域，该物种的分布范围将扩张，且年内出现时间将提前；而在最温暖的区域，其季节适宜性在最热月份会出现下降，这可能导致其物候呈现双峰模式，并在仲夏出现生存空档。
5. 研究总结——本研究利用标本馆记录与逐月气象数据，开发了一种新型物种分布模型，该模型不仅可预测短命物种的适宜分布地点，还可预测该物种在这些区域内的年内适宜出现时间。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，以及如何在景观尺度上影响物种的季节性物候。