CAREER: Pachyderms to pathogens: the cascading effects of megafauna loss on tropical tree recruitment

在世界范围内，狩猎和耕作等人类活动正在减少最大动物的数量，这些动物也被称为“巨型动物”。非洲森林象是一个特别令人担忧的濒临灭绝的物种。这些动物通过传播树木种子、回收和传播其粪便中的营养物质，以及通过食用植被和践踏或连根拔起小树，从而使更多的光线穿透到森林地面，帮助在中非大部分地区创造和维护森林。目前尚不清楚这些生态工程师的消失将如何改变该地区的森林，也不清楚如果没有这些工程师，消耗种子和幼苗的较小哺乳动物、昆虫和真菌是否会更强烈地决定那里生长的树木类型，从而改变森林为人类提供的木材、药物和食物等生态系统服务。这项研究的首要目标是广泛界定大型动物的总体影响，特别是非洲森林大象对封闭式林冠森林的影响。该项目将研究与研究生的教育和培训无缝结合。这项研究验证了这样一种假设，即大型动物的枯竭对剩余的动植物具有连锁效应。研究目标是：评估树木及其相互作用的有机体之间的关系；量化大象的丧失对这些动植物相互作用和树木招募的影响程度；模拟分散在大象中的树种的种群动态，以比较有大象和没有大象的模拟种群的灭绝概率。研究人员将进行三个与目标相对应的主要实验。首先，为了测量植物天敌群体(如真菌)对完整森林中树木招募的相对影响，他们将结合笼养实验和观察，在研究过程中监测苗木、幼树、幼树和成年树木。其次，为了评估违约如何影响植物敌人群体以及森林结构、组成和多样性的相对重要性，他们将在违约的不同梯度上扩大笼养实验，以评估动物种群的减少如何影响树木种群和群落。第三，他们将通过为特定树种建立基于个体的模型，并模拟大象对森林组成和结构的影响，来预测违约对种群和社区层面的影响。这项研究将确定，在大象减少的森林中，大型食草动物的丧失是否将草食动物的相对优势转移到替代的植物捕食者，以及这是否会改变森林动态和生态系统服务。这一奖项反映了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。

Worldwide, human activities such as hunting and farming are reducing the populations of the largest animals, also called "megafauna". A declining species of special concern is the African forest elephant. These animals help create and maintain forests throughout much of central Africa by dispersing tree seeds and recycling and spreading nutrients in their dung, and by eating vegetation and trampling or uprooting small trees, thus allowing more light to penetrate to the forest floor. It is still unknown how the loss of these ecological engineers will change the region's forests or if, in their absence, smaller mammals, insects and fungi that consume seeds and seedlings might more strongly determine the types of trees that grow there and consequently alter the ecosystem services, such as timber, medicine and food, that the forests provide to humans. The overarching goal of this research is to broadly define the impact of megafauna in general, and the African forest elephant specifically, on closed canopy forests. The project seamlessly integrates research with education and training of graduate students. This research tests the hypothesis that the depletion of megafauna has cascading effects on the remaining plants and animals. The research objectives are to: assess the relationship among trees and the organisms with which they interact; quantify the degree to which loss of elephants alters these plant-animal interactions and tree recruitment; and simulate population dynamics of elephant-dispersed tree species to compare extinction probability in simulated populations with and without elephants. The researchers will undertake three major experiments that correspond to the objectives. First, to measure the relative effects of plant enemy groups (such as fungi) on tree recruitment in intact forest, they will combine caging experiments and observations to monitor seedlings, saplings, juveniles and adult trees over the course of the study. Second, to evaluate how defaunation affects the relative importance of plant enemy groups and forest structure, composition and diversity, they will expand the caging experiments across a gradient of defaunation to evaluate how reductions in animal populations affect tree populations and communities. Third, they will forecast the population- and community-level effects of defaunation by building individual based models for specific tree species and modeling the effects of elephants on forest composition and structure. The research will determine whether, in elephant-reduced forests, the loss of large herbivores shifts the relative strengths of herbivory to alternate plant predators, and if this changes forest dynamics and ecosystem services.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.