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类群间巨大差异、丰度和生物量的过程。食物网概括了生态系统中元素和能量的流动。一种基本类型的网络根据共享的猎物和捕食者将分类群划分为营养级别。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上的生物总量。三个生态理论结合在一起，应该有助于我们实现这一目标：资源有限吗？Ofan防守的选择有多强？防御理论猎物如何在增长和防御之间分配？生态化学计量学哪些元素是潜在的资源？1.OFAN(其建筑师的首字母缩写)提出，资源的平衡和捕食者的模仿随着网络基础上可用的资源的数量而不同。生态化学计量学假设，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有效性的平衡。哪些可用元素可以构建防御体系？防御如何塑造元素组成？3.防御理论认为，生长和防御之间的最佳分配取决于捕食的强度和猎物成长到生殖年龄所需的时间。这些理论将被用来探索巴拿马共和国巴罗科罗拉多国家纪念碑(BCNM)中热带垃圾食物网的动态。我们所知道的大部分关于食物网的结构和功能都来自植物性的，或绿色的网。然而，超过80%的固定在热带树冠光合作用中的碳以垃圾的形式落在由微生物、微生物和它们的捕食者组成的棕色食物网中分解。这些网中的分类群可能代表了森林中60%的无脊椎动物，它们的丰富度在小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以及维持森林的大部分生物多样性方面很重要，但我们对这些网络中形成丰富的因素却知之甚少。就像上面的绿色森林树冠一样，热带凋落物代表着地球上最后的生态前沿之一。BCNM拥有广泛的基础设施，它由史密森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学研究，是开展这一项目的最佳地点。生态化学计量学将被用来确定在BCNM的棕色食物网的营养水平和常见分类群中，哪些元素(C、N、Ca、P、S、镁、K、铜、铁、锌)限制了生物量。其50公顷的树块将用于将这些生物量映射到10种常见树种在凋落物分解的三个阶段的化学特征上。这些模式将在长期的40x40m施肥小区和1-m2小区的养分脉冲试验中得到进一步的检验。OFAN关于生物量沿营养梯度阶梯积累的预测将利用上述数据进行评估。它的机制--捕食者限制的影响随着资源的梯度而变化--将通过将捕食性蚂蚁挡在门外的栅栏和用蚂蚁窝补充地块来进行测试。国防理论的生活史权衡将通过测量常见凋落物分类群的生长速度和评估它们对捕食者的适口性在微观上进行评估。如果真菌和微生物的防御显着减少了捕食，那么沿着资源梯度进行的生活史权衡是塑造这个系统中捕食和资源限制的平衡的关键现象。

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.