Barga Sarah, Dilts Thomas E, Leger Elizabeth A
Department of Natural Resources and Environmental Science, University of Nevada, Reno, 1664 N. Virginia Street, MS 186, Reno, NV, USA.
Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, Reno, NV, USA.
Oecologia. 2017 Nov;185(3):437-452. doi: 10.1007/s00442-017-3958-5. Epub 2017 Sep 21.
Spatial and temporal environmental variability can lead to variation in selection pressures across a landscape. Strategies for coping with environmental heterogeneity range from specialized phenotypic responses to a narrow range of conditions to generalist strategies that function under a range of conditions. Here, we ask how mean climate and climate variation at individual sites and across a species' range affect the specialist-generalist spectrum of germination strategies exhibited by 10 arid land forbs. We investigated these relationships using climate data for the western United States, occurrence records from herbaria, and germination trials with field-collected seeds, and predicted that generalist strategies would be most common in species that experience a high degree of climate variation or occur over a wide range of conditions. We used two metrics to describe variation in germination strategies: (a) selectivity (did seeds require specific cues to germinate?) and (b) population-level variation (did populations differ in their responses to germination cues?) in germination displayed by each species. Species exhibited distinct germination strategies, with some species demonstrating as much among-population variation as we observed among species. Modeling efforts suggested that generalist strategies evolve in response to higher spatial variation in actual evapotranspiration at a local scale and in available water in the spring and annual precipitation at a range-wide scale. Describing the conditions that lead to variation in early life-history traits is important for understanding the evolution of diversity in natural systems, as well as the possible responses of individual species to global climate change.
空间和时间上的环境变异性会导致整个景观中选择压力的变化。应对环境异质性的策略范围广泛，从针对狭窄条件范围的专门表型反应到在一系列条件下起作用的通才策略。在这里，我们探讨个体地点以及物种分布范围内的平均气候和气候变化如何影响10种干旱地草本植物所展现的从专性到通性的萌发策略谱。我们利用美国西部的气候数据、植物标本馆的出现记录以及对野外采集种子的萌发试验来研究这些关系，并预测通才策略在经历高度气候变化或在广泛条件下出现的物种中最为常见。我们使用两个指标来描述萌发策略的变化：（a）选择性（种子是否需要特定线索来萌发？）和（b）每个物种所展示的萌发过程中的种群水平变化（种群对萌发线索的反应是否不同？）。物种表现出不同的萌发策略，一些物种在种群间的变化程度与我们在物种间观察到的一样大。建模结果表明，通才策略是为响应局部尺度上实际蒸散量的较高空间变化以及范围尺度上春季可用水量和年降水量的变化而演化的。描述导致早期生活史特征发生变化的条件对于理解自然系统中多样性的演化以及单个物种对全球气候变化的可能反应至关重要。
