Biology Department, University of Washington, Seattle, Washington, 98195, USA.
Ecology. 2017 Nov;98(11):2799-2812. doi: 10.1002/ecy.1996. Epub 2017 Oct 11.
Spatial community reassembly driven by changes in species abundances or habitat occupancy is a well-documented response to anthropogenic global change, but communities can also reassemble temporally if the environment drives differential shifts in the timing of life events across community members. Much like spatial community reassembly, temporal reassembly could be particularly important when critical species interactions are temporally concentrated (e.g., plant-pollinator dynamics during flowering). Previous studies have documented species-specific shifts in phenology driven by climate change, implying that temporal reassembly, a process we term "phenological reassembly," is likely. However, few studies have documented changes in the temporal co-occurrence of community members driven by environmental change, likely because few datasets of entire communities exist. We addressed this gap by quantifying the relationship between flowering phenology and climate for 48 co-occurring subalpine wildflower species at Mount Rainier (Washington, USA) in a large network of plots distributed across Mt. Rainier's steep environmental gradients; large spatio-temporal variability in climate over the 6 yr of our study (including the earliest and latest snowmelt year on record) provided robust estimates of climate-phenology relationships for individual species. We used these relationships to examine changes to community co-flowering composition driven by 'climate change analog' conditions experienced at our sites in 2015. We found that both the timing and duration of flowering of focal species was strongly sensitive to multiple climatic factors (snowmelt, temperature, and soil moisture). Some consistent responses emerged, including earlier snowmelt and warmer growing seasons driving flowering phenology earlier for all focal species. However, variation among species in their phenological sensitivities to these climate drivers was large enough that phenological reassembly occurred in the climate change analog conditions of 2015. An unexpected driver of phenological reassembly was fine-scale variation in the direction and magnitude of climatic change, causing phenological reassembly to be most apparent early and late in the season and in topographic locations where snow duration was shortest (i.e., at low elevations and on ridges in the landscape). Because phenological reassembly may have implications for many types of ecological interactions, failing to monitor community-level repercussions of species-specific phenological shifts could underestimate climate change impacts.
由于物种丰度或栖息地占有率的变化而导致的空间群落重组是对人为全球变化的一种有充分记录的反应，但如果环境导致群落成员的生命事件时间发生差异，群落也可以随时间进行重组。与空间群落重组非常相似，当关键物种相互作用在时间上集中时（例如，开花期间的植物-传粉者动态），时间上的群落重组可能特别重要。先前的研究记录了气候变化驱动的物种特定物候变化，这意味着时间上的重组，我们称之为“物候重组”，很可能发生。然而，很少有研究记录环境变化驱动的群落成员在时间上的共存变化，这可能是因为很少有整个群落的数据存在。我们通过在雷尼尔山（美国华盛顿州）的一个大型网络样地中量化 48 种共存的亚高山野花物种的开花物候与气候之间的关系来解决这一差距，这些样地分布在雷尼尔山的陡峭环境梯度上；我们研究的 6 年中气候的大时空变异性为单个物种的气候-物候关系提供了稳健的估计。我们使用这些关系来研究 2015 年我们站点经历的“气候变化类似”条件对群落共同开花组成的变化。我们发现，焦点物种的开花时间和持续时间都对多个气候因素（融雪、温度和土壤湿度）非常敏感。出现了一些一致的反应，包括较早的融雪和较暖的生长季节导致所有焦点物种的开花物候更早。然而，物种对这些气候驱动因素的物候敏感性存在很大差异，以至于在 2015 年的气候变化类似条件下发生了物候重组。物候重组的一个意外驱动因素是气候变化的方向和幅度的细粒度变化，导致物候重组在季节的早期和晚期以及雪期最短的地形位置（即低海拔和景观中的山脊）最为明显。由于物候重组可能对许多类型的生态相互作用产生影响，如果不监测物种特定物候变化对群落水平的影响，可能会低估气候变化的影响。
