RAPID: Fire-mediated natural experiment on top-down versus bottom-up forces on a vertebrate community

生态学中最长期存在的问题之一是食物的可得性和捕食在多大程度上决定了生态群落中动物的身份和丰度。当食物资源转移到生态系统中时，特别难以确定捕食对当地猎物物种丰度的影响。捕食者的丰度可能增加，导致本地猎物密度下降，或者捕食者可能专注于进口资源，对本地猎物密度影响不大。在巴西的潘塔纳尔湿地，美洲虎专门捕食进口的水生猎物，是陆地专性食肉动物中最嗜食的。此外，在这个不同寻常的潘塔纳尔食物网中，美洲虎是最顶尖的捕食者，是迄今为止数量最多的陆生哺乳动物。然而，目前尚不清楚大型食草动物的低密度是由于可用食物资源不足（自下而上控制）还是由于大量美洲虎的捕食（自上而下控制）。2020年9月的灾难性野火摧毁了潘塔纳尔约30%的树冠植被，以及PI先前在潘塔纳尔保护区Taiama建立的研究地点约50%的植被。冠层的移除刺激了早期一些有营养的植被的生长。通过比较燃烧和未燃烧地区以及火灾前后哺乳动物食草动物的丰度，PI将能够确定这个食物网是由自上而下还是自下而上的力量控制的。该项目位于巴西马托格罗索州土地利用/气候变化关系的核心，该地区是世界上最大的大豆和牛肉出口国。了解这一系统的动态至关重要，因为人们普遍预测，由于气候变化和大规模耕地侵占，潘塔纳尔地区的火灾将变得更加频繁和严重。此外，这项工作将有助于研究生的教育，并促进美国和巴西科学家之间正在进行的合作。pi将使用控制-影响前-后（BACI）设计来询问(1)专门捕食水生猎物的美洲豹是否减少了对陆生物种的捕食压力，或者(2)水生动物对美洲豹的补贴是否导致捕食增加，从而抑制了食草哺乳动物的数量。比较4年的火灾前后数据（影响前后），以及保护区内未燃烧和燃烧区域（控制影响），将使PI确定以美洲虎为顶端食肉动物的食物网是由自上而下还是自下而上的力量调节的。从2021年9月（火灾一年后）开始，pi将量化植被再生、陆地和水生猎物物种丰度、美洲虎密度和饮食，为期一年。快速再生生长在该地区是典型的，因此提出研究的时机至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the most longstanding questions in ecology is the degree to which food availability and predation determine the identity and abundance of animals in ecological communities. When food resources are transferred into ecosystems it is especially difficult to determine the effect of predation on local prey species abundance. Predator abundance may increase, leading to decreased local prey density, or predators may specialize on imported resources and have little effect on local prey density. In the Pantanal wetlands of Brazil jaguars specialize on imported aquatic prey and have the most picivorous diet of any terrestrial obligate carnivore. Moreover, in this unusual Pantanal food web jaguars, the apex predator, are by far the most abundant terrestrial mammal species. However, it is unclear if the low density of large herbivores is due to low available food resources (bottom-up control) or predation especially by the abundant jaguars (top-down control). Catastrophic wildfires in September 2020 removed canopy vegetation from about 30% of the Pantanal and about 50% of the PI’s previously established study sites at Taiama, a protected area in the Pantanal. Canopy removal stimulates a flush of nutritious early seral vegetation. By comparing mammalian herbivore abundance in burned and unburned areas, and before and after the fire, the PI will be able to determine if this food web is controlled by top-down or bottom-up forces. This project lies at the heart of the land-use/climate change nexus in the Mato Grosso region of Brazil, the world's largest soy and bovine beef exporter. Understanding the dynamics of this system is critical as fires in the Pantanal are widely predicted to become more frequent and increasingly severe due to both climate change and large-scale cropland encroachment. In addition, this work will contribute to the education of a graduate student and further an ongoing collaboration between US and Brazilian scientists. The PIs will use a before–after-control–impact (BACI) design to ask whether (1) jaguars specializing on aquatic prey have reduced predation pressure on terrestrial species, or (2) whether aquatic subsidies to jaguars lead to increased predation that suppresses mammalian herbivore populations. Comparison of 4-years of pre-fire data to post-fire data (before-after impact), as well as unburnt and burnt areas (control-impact) within the reserve, will allow the PI to determine if the food web in which the jaguar is the apex carnivore is mediated by top-down or bottom-up forces. The PIs will quantify vegetation regeneration, terrestrial and aquatic prey species abundance, and jaguar density and diet for one year starting in September 2021 (one year after the fires). Fast regenerative growth is typical in this region making the timing of the proposed study critical.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.