Effects of phenological mismatch under warming are modified by community context

Climate change is altering the relative timing of species interactions by shifting when species first appear in communities and modifying the duration organisms spend in each developmental stage. However, community contexts, such as intraspecific competition and alternative resource species, can prolong shortened windows of availability and may mitigate the effects of phenological shifts on species interactions. Using a combination of laboratory experiments and dynamic simulations, we quantified how the effects of phenological shifts in Drosophila-parasitoid interactions differed with concurrent changes in temperature, intraspecific competition, and the presence of alternative host species. Our study confirmed that warming shortens the window of host susceptibility. However, the presence of alternative host species sustained interaction persistence across a broader range of phenological shifts than pairwise interactions by increasing the degree of temporal overlap with suitable development stages between hosts and parasitoids. Irrespective of phenological shifts, parasitism rates declined under warming due to reduced parasitoid performance, which limited the ability of community context to manage temporally mismatched interactions. These results demonstrate that the ongoing decline in insect diversity may exacerbate the effects of phenological shifts in ecological communities under future global warming temperatures.

Methods
We experimentally manipulated the timing of host-parasitoid interactions in current and expected warming temperatures. We did this in high and low levels of resource competition and in simple and complex communities. We also used this data to parameterize a multigenerational dynamic model to investigate the long-term consequences of phenological shifts.

气候变化通过改变物种在群落中首次出现的时间，并调整生物在各发育阶段的持续时长，改变了物种间相互作用的相对时序。然而，群落背景（如种内竞争（intraspecific competition）与替代资源物种（alternative resource species））可延长被缩短的可利用窗口，并缓解物候变化（phenological shifts）对物种互作的影响。本研究结合室内实验与动态模拟，量化了果蝇-寄生蜂互作（Drosophila-parasitoid interactions）的物候变化效应如何随温度的同步变化、种内竞争及替代寄主物种的存在而产生差异。研究证实，气候变暖缩短了宿主易感性（host susceptibility）窗口；但相较于两两互作，替代寄主物种的存在通过提升宿主与寄生蜂间适宜发育阶段的时间重叠度，在更广泛的物候变化范围内维持了互作的持久性。无论物候变化与否，由于寄生蜂性能下降，变暖环境下的寄生率（parasitism rates）均会降低，这限制了群落背景调控时序错配互作的能力。本研究结果表明，在未来全球变暖的温度条件下，昆虫多样性的持续下降可能会加剧生态群落中物候变化的影响。

研究方法
本研究在当前与预期变暖的温度条件下，对宿主-寄生蜂互作的时序进行了实验操控。实验设置了高、低两级资源竞争水平，以及简单与复杂两类群落结构。本研究同时利用所得实验数据参数化了多世代动态模型（multigenerational dynamic model），以探究物候变化带来的长期后果。