Global change drivers can interact in synergistic ways, yet the interactive effect of global change drivers, such as climatic warming and species invasions, on plant pollination are poorly represented in experimental studies. We paired manipulative experiments to probe two mechanistic pathways through which plant invasion and warming may alter phenology and reproduction of native plant species. In the first, we tested how experimental warming (+1.7°C) modulated flowering phenology and how this affected flowering overlap between a native plant (Dracophyllum subulatum) and an invasive plant (Calluna vulgaris L.). In the second experiment we explored how variation in the ratio of native to invasive flowers, and the overall quantity of resources in a floral patch, affected the reproduction of the native species. We hypothesised that the flowering overlap of native and invasive plants would be altered by warming, given that invading plants typically exhibit greater phenological plasticity than native plants. Further, we hypothesised that pollination of native plant flowers would decrease in floral patches dominated by invasive plant flowers, but that this effect would depend on total floral density in the patch. As predicted, the invasive plant had a stronger phenological response to experimental warming than the native plant, resulting in increased flowering overlap between the native the invasive plants. There was a four-fold increase in the number of native flowers co-flowering with high densities of invasive flowers suggesting native plant competition for pollinators with invasive plants under a warmed climate. In the second experiment, we found depressed seed weights of the native species in high density floral patches that were dominated by invasive flowers relative to high density floral patches dominated by native flowers. At low floral densities, seed weight of native plants was unaffected by invasion. Together, these results demonstrate that by increasing their phenological overlap, warming may enhance the magnitude of existing competition for pollination exerted by an invasive plant on a native plant, particularly in plant patches with high floral density. Our results illustrate a novel pathway through which global change drivers can operate synergistically to alter an important ecosystem service - pollination.

中文翻译：

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气候变化和入侵可能会协同影响本地植物繁殖

全球变化驱动因素可以以协同方式相互作用，但在实验研究中，气候变暖和物种入侵等全球变化驱动因素对植物授粉的相互作用影响很少。我们配对操作实验来探索植物入侵和变暖可能改变本地植物物种的物候和繁殖的两种机制途径。首先，我们测试了实验性升温 (+1.7°C) 如何调节开花物候，以及这如何影响本地植物 (Dracophyllum subulatum) 和入侵植物 (Calluna vulgaris L.) 之间的开花重叠。在第二个实验中，我们探讨了本地花卉与入侵花卉的比例以及花块中资源总量的变化如何影响本地物种的繁殖。我们假设本地植物和入侵植物的开花重叠会因变暖而改变，因为入侵植物通常比本地植物表现出更大的物候可塑性。此外，我们假设在以入侵植物花为主的花块中，原生植物花的授粉会减少，但这种影响将取决于花块中的总花密度。正如预测的那样，入侵植物对实验变暖的物候响应比本地植物更强，导致本地入侵植物之间的开花重叠增加。与高密度入侵花卉共同开花的本土花卉数量增加了四倍，这表明本土植物在温暖气候下与入侵植物竞争传粉媒介。在第二个实验中，我们发现，相对于以原生花为主的高密度花块，在以入侵花为主的高密度花块中，本地物种的种子重量降低。在低花密度下，本地植物的种子重量不受入侵的影响。总之，这些结果表明，通过增加它们的物候重叠，变暖可能会增强入侵植物对本地植物施加的现有授粉竞争的程度，特别是在具有高花卉密度的植物斑块中。我们的结果说明了一种新途径，通过该途径，全球变化驱动因素可以协同运作以改变重要的生态系统服务——授粉。