The ecological and evolutionary legacy of extreme climatic events for food web resilience

越来越多的证据表明，热浪等极端事件，而不是平均气温的上升，将对动植物产生最直接和有害的影响。对于物种丰富的热带生态系统来说尤其如此，最近的热浪已经造成了一些物种的严重种群崩溃，大多数调查极端气候事件对生物多样性影响的研究都集中在孤立的单个物种上。然而，自然群落是复杂的、相互作用的物种网络，通过竞争、互利共生、捕食和寄生联系在一起。因此，我们需要了解当整个相互作用的物种群落受到热浪或其他极端气候事件的影响时会发生什么，以及这些影响如何根据事件的持续时间和强度而变化。从长远来看，当面临进一步的极端情况时，幸存的种群和物种的适应能力如何？答案可能取决于生态反应（不同物种的丰度和相互作用的变化取决于其生态耐受性）和进化过程（通过自然选择进化出新的耐受性）。为了充分理解极端事件如何以及为什么改变生态群落，我们需要进行模拟极端条件的实验，并跟踪多代人的后果。在大多数情况下，这样的实验在实践上或道德上是不可能的。然而，我们可以通过专注于一个特殊的研究系统来设计这样的实验：果蝇和寄生蜂的食物网。在我们的研究地点，在澳大利亚热带昆士兰州的热带雨林中，这些苍蝇和黄蜂在腐烂的水果中形成了离散的生态群落。它们的世代时间很短，使我们能够在真实的时间内观察社区对极端气候的反应。澳大利亚热带雨林是一个高度多样性的生态系统，受到气候变化的威胁，我们预计热带雨林昆虫特别脆弱，因为它们已经接近其耐热性的上限：温度的适度进一步上升可能使种群和社区无法生存。这些特性使我们的研究系统非常适合了解生态系统对极端气候事件的适应能力。在我们的实验中，我们将在雨林中使用加热电缆来模拟预计将在未来几十年影响澳大利亚雨林的热浪条件。然后，我们将研究个别物种的生态和进化反应，以及它们之间相互作用的食物网对进一步扰动的反应。通过用更多的热浪来挑战以前遭受热浪的社区，我们将能够测试在什么条件下极端气候使社区对未来冲击的适应力更强或更弱，并了解支撑社区适应力的生态和进化机制。

There is growing evidence that extreme events such as heatwaves, rather than increases in average temperatures, will have the most immediate and harmful effects on plants and animals. This is particularly true for species-rich tropical ecosystems, where recent heatwaves have already caused severe population crashes for some species.Most studies investigating the impact of extreme climatic events on biodiversity focus on individual species in isolation. However, natural communities are complex, interacting networks of species, linked by competition, mutualism, predation and parasitism. We therefore need to understand what happens when whole communities of interacting species are subjected to a heatwave or other extreme climatic event, and how these effects change depending on the duration and intensity of the event. How resilient will the surviving populations and species be in the longer term, when faced with further extremes? The answer is likely to depend on both ecological responses (changes in the abundance and interactions of different species depending on their ecological tolerances), and evolutionary processes (the evolution of novel tolerances through natural selection). To understand fully how and why ecological communities are altered by extreme events, we need to carry out experiments simulating extreme conditions and follow the consequences over multiple generations. In most contexts such experiments would be practically or ethically impossible. However, we can design experiments that do exactly this by focusing on a special study system: food webs of Drosophila fruit flies and the parasitic wasps that consume them. At our study site in the rainforests of tropical Queensland, Australia, these flies and wasps form discrete ecological communities within individual rotting fruits. They have short generation times, allowing us to observe community responses to climate extremes in real time. Australian tropical rainforests are a high-diversity ecosystem that is threatened by climate change, and we expect rainforest insects to be particularly vulnerable because they are already operating close to the upper limits of their thermal tolerances: modest further increases in temperatures could make populations and communities unviable. These characteristics make our study system ideal for understanding the resilience of ecological systems to extreme climatic events.In our experiments, we will use heating cables in the rainforest to simulate heatwave conditions that are expected to affect Australian rainforests in the coming decades. We will then investigate the ecologically and evolutionary responses of individual species and the food web of interactions among them to further perturbations. By challenging communities that have previously been subjected to heat waves with further heat waves, we will be able to test under what conditions climatic extremes make communities more or less resilient to future shocks and understand the ecological and evolutionary mechanisms that underpin community resilience.