Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106, USA.
Ecology. 2011 Dec;92(12):2236-47. doi: 10.1890/11-0471.1.
A major challenge in forecasting the ecological consequences of climate change is understanding the relative importance of changes to mean conditions vs. changes to discrete climatic events, such as storms, frosts, or droughts. Here we show that the first major storm of the growing season strongly influences the population dynamics of three rare and endangered annual plant species in a coastal California (USA) ecosystem. In a field experiment we used moisture barriers and water addition to manipulate the timing and temperature associated with first major rains of the season. The three focal species showed two- to fivefold variation in per capita population growth rates between the different storm treatments, comparable to variation found in a prior experiment imposing eightfold differences in season-long precipitation. Variation in germination was a major demographic driver of how two of three species responded to the first rains. For one of these species, the timing of the storm was the most critical determinant of its germination, while the other showed enhanced germination with colder storm temperatures. The role of temperature was further supported by laboratory trials showing enhanced germination in cooler treatments. Our work suggests that, because of species-specific cues for demographic transitions such as germination, changes to discrete climate events may be as, if not more, important than changes to season-long variables.
预测气候变化对生态影响的一个主要挑战是理解均值变化与离散气候事件（如风暴、霜冻或干旱）变化的相对重要性。本研究表明，生长季的第一场主要风暴强烈影响了加利福尼亚州（美国）沿海生态系统中三种稀有濒危一年生植物的种群动态。在一项野外实验中，我们使用水分屏障和补水来操纵与季节首场大雨相关的时间和温度。三个焦点物种在不同风暴处理之间的个体种群增长率存在 2 到 5 倍的变化，与先前实验中在长达一个季节的降水量上施加 8 倍差异所发现的变化相当。萌发的变化是两个三种物种对第一场雨的响应的主要人口驱动因素之一。对于其中一种物种来说，风暴的时间是其萌发的最关键决定因素，而另一种则在较冷的风暴温度下表现出增强的萌发。实验室试验进一步支持了温度的作用，表明在较冷的处理中萌发增强。我们的工作表明，由于特定物种的人口转变（如萌发）的线索，离散气候事件的变化可能与季节性变量的变化一样重要，甚至更重要。
