International Center for Coral Reef Research and Restoration, Mote Marine Laboratory, Summerland Key, FL, USA.
Department of Biological Sciences and Center for Coastal Oceans Research, Florida International University, Miami, FL, USA.
J Anim Ecol. 2021 Sep;90(9):2041-2052. doi: 10.1111/1365-2656.13424. Epub 2021 Feb 23.
Extreme climatic events (ECEs) and predator removal represent some of the most widespread stressors to ecosystems. Though species interactions can alter ecological effects of climate change (and vice versa), it is less understood whether, when and how predator removal can interact with ECEs to exacerbate their effects. Understanding the circumstances under which such interactions might occur is critical because predator loss is widespread and ECEs can generate rapid phase shifts in ecosystems which can ultimately lead to tropicalization. Our goal was to determine whether loss of predation risk may be an important mechanism governing ecosystem responses to extreme events, and whether the effects of such events, such as tropicalization, can occur even when species range shifts do not. Specifically, our goal was to experimentally simulate the loss of an apex predator, the tiger shark Galeocerdo cuvier effects on a recently damaged seagrass ecosystem of Shark Bay, Australia by applying documented changes to risk-sensitive grazing of dugong Dugong dugon herbivores. Using a 16-month-field experiment established in recently disturbed seagrass meadows, we used previous estimates of risk-sensitive dugong foraging behaviour to simulate altered risk-sensitive foraging densities and strategies of dugongs consistent with apex predator loss, and tracked seagrass responses to the simulated grazing. Grazing treatments targeted and removed tropical seagrasses, which declined. However, like in other mixed-bed habitats where dugongs forage, treatments also incidentally accelerated temperate seagrass losses, revealing that herbivore behavioural changes in response to predator loss can exacerbate ECE and promote tropicalization, even without range expansions or introductions of novel species. Our results suggest that changes to herbivore behaviours triggered by loss of predation risk can undermine ecological resilience to ECEs, particularly where long-lived herbivores are abundant. By implication, ongoing losses of apex predators may combine with increasingly frequent ECEs to amplify climate change impacts across diverse ecosystems and large spatial scales.
极端气候事件 (ECEs) 和捕食者移除是对生态系统影响最广泛的压力因素之一。尽管物种相互作用可以改变气候变化的生态效应（反之亦然），但人们对于捕食者移除是否以及如何与 ECE 相互作用从而加剧其影响知之甚少。了解这种相互作用可能发生的情况至关重要，因为捕食者的丧失是广泛存在的，而 ECE 可以导致生态系统发生快速的阶段转变，最终导致热带化。我们的目标是确定捕食风险的丧失是否可能是控制生态系统对极端事件响应的重要机制，以及即使物种范围没有发生变化，这些事件的影响（如热带化）是否也会发生。具体来说，我们的目标是通过应用文献中记录的对风险敏感的食草动物儒艮 Dugong dugon 的放牧行为的改变，实验模拟顶级掠食者虎鲨 Galeocerdo cuvier 的丧失对澳大利亚鲨鱼湾最近受损的海草生态系统的影响。我们在最近受到干扰的海草草地中进行了为期 16 个月的野外实验，利用先前对风险敏感的儒艮觅食行为的估计，模拟了与顶级掠食者丧失一致的、风险敏感的儒艮觅食密度和策略的改变，并跟踪了海草对模拟放牧的响应。放牧处理针对并去除了热带海草，这些海草减少了。然而，就像在其他儒艮觅食的混合床栖息地一样，处理也意外地加速了温带海草的损失，这表明食草动物行为的改变是对捕食者丧失的响应，可以加剧 ECE 并促进热带化，即使没有范围扩大或引入新物种。我们的研究结果表明，由捕食风险丧失引发的食草动物行为的改变可能会破坏生态系统对 ECE 的恢复能力，特别是在长寿食草动物丰富的情况下。这意味着，顶级掠食者的持续丧失可能与越来越频繁的 ECE 一起，在不同的生态系统和大的空间尺度上放大气候变化的影响。
