Collaborative Research: Effects of top scavenger declines – from microbes to ecosystems

除非首先被捕食者吃掉，否则所有的动物在死亡时都会进入腐肉池。清道夫和微生物在将来自身体的营养物质返回土壤的过程中发挥着关键作用，在土壤中它们被回收利用，用于植物的吸收和生长。腐肉投入对营养循环、食物网络动态和生态系统碳平衡的影响仍然是一个谜。随着包括食腐动物在内的许多物种在全球范围内的减少，量化腐肉衍生营养物质的数量和质量如何塑造植物群落结构和生态系统动态是至关重要的。塔斯马尼亚魔鬼是研究觅食对生态系统过程的影响的理想物种和魅力物种。它们是世界上为数不多的吃骨头的食肉动物之一。通过加速关键植物生长限制养分的循环，否则这些养分将被锁定在骨骼材料中多年，塔斯马尼亚魔鬼提供了关键的生态系统功能。近年来，一种高度可传播的癌症-魔鬼面部肿瘤疾病(DFTD)的出现极大地减少了塔斯马尼亚东部的魔鬼种群数量，并蔓延到全岛，威胁到这个标志性物种的灭绝。研究人员将利用这一悲惨的情况来测试是否可以在生态系统规模上检测到魔鬼拾取的影响，以及魔鬼数量的下降如何导致其他拾荒者物种角色的转变。该项目将在国际背景下为美国研究生和博士后学者提供培训机会。通过教育和推广活动，研究人员将强调清道夫、生物多样性和生态系统复原力之间存在的联系。很少有研究直接调查非植物投入对食物网络内能量转移的影响。因此，在理解腐肉和食腐动物协会如何在生态系统规模上管理生物地球化学循环方面，存在着相当大的知识差距。在塔斯马尼亚，DFTD从东向西扩散，这是一种致命的、可传播的癌症，威胁着魔鬼的灭绝，并在全岛造成了人口密度梯度(从承载能力的0%到100%)。由此产生的“自然实验”提供了一个难得的机会来研究顶端清道夫的下降如何改变食物网内的能量转移和营养在腐肉、土壤和植物中的流动。将在五个研究地点建立高频监测和采样站，这些研究地点跨越DFTD梯度，并捕获四种实验处理：(1)完全清道夫(堆积的猎物身体)；(2)魔鬼排除(除魔鬼之外的所有食腐动物)；(3)重建的魔鬼厕所，以捕获来自局部粪便的营养脉冲；(4)仅土壤对照，以监测本底C和养分供应。身体上的魔鬼和中食动物的密度将使用相机阵列进行估计；无脊椎动物的密度将使用适当的昆虫陷阱进行评估。稳定同位素示踪将被用来跟踪身体衍生的营养物质如何影响微生物群落多样性和土壤碳的形成。将估计每个地点和整个大陆DFTD梯度的植物生产力(NPP)、叶片质量、苗木招募和细根生物量。利用魔鬼种群减少的程度和时间的时空变化，将利用一系列规模化实验：(1)确定食腐动物密度的变化如何影响当地土壤的生物地球化学；(2)调查腐肉和食腐网络如何导致微生物群落的新陈代谢效率和新植物凋落物投入的分解率的变化；(3)测试可检测到魔鬼觅食的规模；以及(4)整合野外和实验室实验的结果，以预测生物多样性丧失将如何影响未来50年的生态系统功能。该项目将支持一个由职业生涯早期的女科学家领导的团队，参与国际合作，并提供研究生和博士后水平的培训。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Unless first consumed by a predator, all animals enter the carrion pool when they die. Scavengers and microorganisms play a critical role in returning carcass-derived nutrients to the soil where they get recycled and used for plant uptake and growth. The impact of carrion inputs on nutrient cycling, food web dynamics, and ecosystem carbon balance remains a mystery. With global declines of many species including scavengers, it is essential to quantify how the quantity and quality of carrion-derived nutrients shapes plant community structure and ecosystem dynamics. Tasmanian devils are an ideal and charismatic species with which to study the effects of scavenging on ecosystem processes. They are one of a few carnivores worldwide that consume bones. By accelerating the cycling of key plant growth-limiting nutrients that would otherwise remain locked in bone material for years, Tasmanian devils provide a critical ecosystem function. In recent years, the emergence of a highly transmissible cancer — devil facial tumor disease, or DFTD — has dramatically reduced devil population sizes in eastern Tasmania and has spread throughout the island, threatening this iconic species with extinction. Researchers will use this tragic situation to test whether devil-scavenging impacts can be detected on an ecosystem scale and how devil population declines result in a shift in the role of other scavenger species. This project will provide training opportunities for US graduate students and post-doctoral scholars in an international setting. Through education and outreach activities, researchers will highlight the linkages that exist between scavengers, biodiversity, and ecosystem resiliency. Few studies have directly investigated the effects of non-plant inputs on energy transfer within food web networks. As a result, there is a considerable knowledge gap in understanding how carrion and scavenger guilds govern biogeochemical cycling at an ecosystem scale. In Tasmania, the east to west spread of DFTD, a lethal, transmissible cancer, threatens devils with extinction and has created a population density gradient across the island (from 0% to 100% of carrying capacity). The resulting 'natural experiment' offers a rare opportunity to study how apex scavenger declines alter energy transfer within food webs and nutrient flows through carrion, soils, and plants. High-frequency monitoring and sampling stations will be established at five study sites that span the DFTD gradient and capture four experimental treatments: (1) full scavenger access (staked prey carcass); (2) devil exclusion (fenced prey carcass allowing access to all scavengers but devils); (3) reconstructed devil latrines to capture nutrient pulses from localized scat; (4) and soil-only controls to monitor background C and nutrient availability. Devil and mesopredator densities at carcasses will be estimated using camera arrays; invertebrate densities will be assessed using appropriate insect traps. Stable isotope tracing will be used to track how carcass-derived nutrients influence microbial community diversity and soil carbon formation. Plant productivity (NPP), leaf quality, seedling recruitment, and fine root biomass will be estimated at each site and across the continental DFTD gradient. Using temporal and spatial variation in the extent and timing of devil population declines, a series of scaled experiments will be used to: (1) determine how variation in scavenger densities affects local soil biogeochemistry; (2) investigate how carrion and scavenging networks induce shifts in the metabolic efficiency of microbial communities and decomposition rates of new plant litter inputs; (3) test the scale at which scavenging by devils is detectable; and (4) integrate findings from field and laboratory experiments to predict how biodiversity loss will affect ecosystem function over the next 50 years. The project will support a team led by an early-career female scientist, involve international collaboration and provide training at the graduate student and postdoctoral levels.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.