Does Ecological Stoichiometry and Defense Theory Predict Patterns of Resource and Predator Limitation in a Tropical Litter Food Web?

生态学的一个基本目标是了解在时间和空间上产生物种间丰富度和生物量巨大变化的过程。食物网概括了生态系统中元素和能量的流动。一种基本的网络类型是根据共同的猎物和捕食者将分类群划分为营养等级。生态学的一个重要和可实现的目标是在时间和空间上预测这些营养水平的生物量。三个生态理论结合在一起，应该可以帮助我们实现这个目标：资源是有限的吗？防守的选择有多强？防御理论猎物是如何在生长和防御之间进行分配的？生态化学计量学哪些元素是潜在资源？OFAN（其架构师的首字母缩写）提出，资源和捕食者模仿的平衡随着网络基础上可用资源的数量而变化。生态化学计量学认为，限制生物量的资源反映了生长和防御所需的化学元素相对于它们在环境中的可用性的平衡。什么可用的元素可以建立防御？防御是如何塑造元素构成的？防御理论认为，生长和防御之间的最佳分配是由捕食的强度和猎物生长到繁殖年龄所需的时间决定的。这些理论将用于探索巴拿马共和国巴罗科罗拉多国家纪念碑（BCNM）热带垃圾食物网的动态。我们对食物网的结构和功能的了解大多来自植物网或绿色网。然而，超过80%的碳在热带冠层的光合作用中以凋落物的形式被分解，在微生物、微生物动物及其捕食者的棕色食物网中被分解。这些网中的分类群可能代表了森林中60%的无脊椎动物，它们的丰度在小的空间尺度上可以变化100倍。然而，尽管它在向大气中释放碳、循环利用生态系统养分和维持大部分森林生物多样性方面很重要，但我们对这些网络中形成丰度的因素却一无所知。就像它上面的绿色森林树冠一样，热带凋落物代表了地球上最后的生态边界之一。BCNM拥有广泛的基础设施，由史密森尼热带研究所长达一个世纪的管理，以及正在进行的大规模实验和人口统计研究，是开展这个项目的最佳地点。生态化学计量学将用于确定哪些元素（在C、N、Ca、P、S、Mg、K、Cu、Fe、Zn中）限制了bcnm棕色食物网的营养水平和常见分类群的生物量。其50公顷的树木地块将用于将这些生物量映射到凋落物分解三个阶段的10种常见树种的化学特征上。这些模式将在40 × 40米的长期施肥地块和1 × 2米的地块上进行进一步的试验测试。OFAN对生物量沿养分梯度阶梯积累的预测将根据上述数据进行评估。它的机制——捕食者限制的影响会随着资源梯度而变化——将通过栅栏来测试，栅栏可以防止捕食蚂蚁进入，并通过在地块上添加蚁窝来补充。防御理论的生活史权衡将在微观世界中通过测量常见凋落物分类群的生长速率和评估它们对捕食者的适口性来评估。如果真菌和微生物的防御显著减少了捕食，那么沿着资源梯度发挥的生活史权衡是形成该系统中捕食和资源限制平衡的关键现象。

A basic goal of ecology is to understand the processes that generate the vast variation inabundance and biomass among taxa in time and space. Food webs summarize the flow of elementsand energy in ecological systems. One basic type of web groups taxa into trophic levels based onshared prey and predators. A significant and attainable goal for Ecology is to predict the biomassacross these trophic levels in time and space. Three ecological theories, knit together, should help us achieve this goal:Are resources limiting? OFANHow strong is selection for defense? Defense theoryHow do prey allocate between growth and defense? Ecological stoichiometryWhich elements are potential resources?1. OFAN (an acronym for its architects) proposes that the balance of resource and predator imitation varies with the amount of resources available at the base of the web.2. Ecological stoichiometry posits that resources limiting biomass reflect the balance of chemical elements needed for growth and defense relative to their availability in the environment. What available elements can build defenses? How do defenses shape elemental composition?3. Defense theory posits that the optimal allocation between growth and defense is determined bythe intensity of predation and the time it takes for the prey to grow to reproductive age.These theories will be used to explore the dynamics of tropical litter food webs in the Republic ofPanama's Barro Colorado National Monument (BCNM). Most of what we know about the structureand function of food webs comes from plant-based, or green webs. However, over 80% of thecarbon fixed in photosynthesis in the tropical canopy falls as litter where it is decomposed in thebrown food web of microbes, microbivores, and their predators. The taxa in these webs mayrepresent 60% of the forest's invertebrates and their abundance can vary 100-fold at small spatialscales. Yet, despite its importance in releasing carbon into the atmosphere, recycling ecosystemnutrients, and sustaining much of the forest's biodiversity, we are profoundly ignorant of the factors shaping abundance in these webs. Like the green forest canopy above it, the tropical litter represents one of the last ecological frontiers on the planet.BCNM, with its extensive infrastructure, its century-long stewardship by Smithsonian TropicalResearch Institute, and its ongoing large-scale experimental and demographic studies, is the bestplace to undertake this project. Ecological stoichiometry will be used to identify which elements(among C, N, Ca, P, S, Mg, K, Cu, Fe, Zn) limit biomass in the trophic levels and common taxa ofBCNM's brown food webs. Its 50 ha tree plot will be used to map this biomass onto the chemicalsignatures of 10 common tree species at three stages of litter decomposition. These patterns will befurther tested experimentally with long-term 40 x 40 m fertilization plots, and pulses of nutrients in1-m 2 plots. OFAN's prediction of a stairstep accumulation of biomass along nutrient gradients will be evaluated with the above data. Its mechanism--that the impact of predator limitation varies along resource gradients--will be tested using fences that keep out predacious ants and by supplementing plots with litter ant nests. Defense' theory's life history tradeoffs will be evaluated in microcosms by measuring growth rates of common litter taxa and evaluating their palatability to predators. If defenses by fungi and microbivores significantly curtail predation then life history tradeoffs that play out along resource gradients are a key phenomenon shaping the balance of predation and resource limitation in this system.