Data from: Individual resource limitation combined with population-wide pollen availability drives masting in the valley oak (Quercus lobata)

1. Masting, the synchronized production of variable seed crops, is widespread among woody plants, but there is no consensus about the underlying proximate mechanisms. To understand this population-level behavior, it is necessary to dissect the behavior of individual trees as well as the interactions that synchronize them. 2. Here we test a model of masting in which variability in seed set is driven by resource limitation within trees and synchrony is driven by pollen limitation due to phenological asynchrony in some years. 3. We used a 35-year seed set data set and a 12-year phenological data set to analyze seed production of 84 valley oaks (Quercus lobata) in central coastal California. Individual trees varied tremendously in their seed production patterns; trees with high levels of seed production were less variable over time, but showed stronger negative autocorrelation between years, suggesting that they are more resource-limited than unproductive trees. In years of more asynchronous flowering, Q. lobata produced fewer seeds, consistent with the importance of phenological synchrony. 4. We parametrized a model with these results to investigate how individual resource limitation and population-wide pollen limitation – a consequence of asynchronous flowering during cold spring temperatures – interact to shape annual variation in seed production. The model illustrates that this proximate abiotic driver can synchronize the behavior of individuals, resulting in population-wide seed production patterns that closely resemble the field data. 5. Synthesis: Our findings support the hypothesis that an interaction between two proximate mechanisms, individual resource limitation and environmental variation affecting population-wide pollen availability, drives masting in this population of Quercus lobata. This combination of internal and external proximate drivers may underlie masting behavior in many wind-pollinated plants.

1. 结实同步现象（masting）指木本植物同步产出可变规模种子的行为，该现象在木本植物中广泛分布，但学界对其背后的近因机制尚未形成统一共识。为解析这一种群级行为，我们有必要拆解单株树木的结实特征，以及驱动个体间同步性的相互作用过程。
2. 本文我们对一则结实同步模型展开检验：该模型认为，结实量的变异由植株内部的资源限制所驱动，而种群同步性则由部分年份物候异步性引发的花粉限制所主导。
3. 我们依托一项为期35年的结实量数据集与一项为期12年的物候数据集，对美国加利福尼亚州中部海岸区域的84株山谷栎（Quercus lobata）的种子生产情况进行分析。结果显示，单株树木的结实模式存在显著差异：结实量较高的植株，其年度结实变异程度更低，但年际间负自相关性更强，这表明相较于低产植株，高产植株受到的资源限制更为严格。在开花物候更为异步的年份，山谷栎的种子产量更低，这与物候同步性的重要性假说相符。
4. 我们基于上述研究结果对模型进行参数化，以此探究个体资源限制与种群尺度花粉限制——即春季低温导致开花异步性的后果——二者如何共同作用，塑造种子生产的年度变异。模型结果表明，这一非生物近因驱动因子能够同步个体的结实行为，最终形成与野外观测数据高度吻合的种群级种子生产模式。
5. 综合讨论：本研究结果支持下述假说，即两种近因机制的交互作用——个体资源限制与影响种群花粉可用性的环境变异——共同驱动了该山谷栎种群的结实同步现象。这种内、外近因驱动因子的组合，或许是众多风媒植物产生结实同步行为的底层机制。