Consequences of herbivore extinction for plant population and community dynamics

人类活动正在以前所未有的速度造成灾害。虽然我们经常拥有关于其原因的详细知识，但缺乏关于灭绝对生态系统后果的信息。我和我的研究小组致力于了解大型食草动物的灭绝如何影响非洲稀树草原的植物种群。我们在肯尼亚莱基皮亚的研究基地包括一个理想的系统，在其中研究这种预防的后果。莱基皮亚由10，000平方公里的私人财产组成，其中每个财产都与反映脊椎动物群落典型的渐进式，大小偏向灭绝的三种情况之一有关：1）大象（~3000公斤）+黑斑羚（~70公斤）+ dik-dik（~5公斤）; 2）黑斑羚+ dik-dik;或3）dik-dik。使用一系列半透性的带电围栏，我和我的研究小组正在模拟上述灭绝场景，以解决大型哺乳动物食草动物如何影响相思树的丰度和分布，这是稀树草原火灾频率，营养循环和生物多样性的关键决定因素。具体地说，我们正在努力回答以下问题：1）大型哺乳动物的捕食如何改变热带稀树草原树木的授粉？2)大型哺乳类食草动物对热带稀树草原树木的种子生产、萌发和补充的影响如何影响树木的种群增长？和3）相对于非生物因素的变化（例如，降雨）？为了解决前两个问题，我和我的研究小组正在将实地实验与空间统计和矩阵模型相结合。为了解决第三个问题，我们正在对肯尼亚中部降雨量五倍梯度的矩阵模型进行“地面实况”预测。因此，我和我的研究小组将阐明生态系统保护的后果。此外，通过实地实验，长期观察和统计建模的结合，我们将开发和完善预测植物种群和群落灭绝后果的工具。

Human activities are causing extinctions to occur at unprecedented rates. Although we often possess detailed knowledge about their causes, a dearth of information exists regarding the consequences of extinction for ecological systems. My research group and I work to understand how extinctions of large herbivores affect plant populations in African savannas. Our study sites in Laikipia, Kenya comprise an ideal system in which to study the ramifications of such extinctions. Laikipia consists of a 10,000 square km mosaic of private properties, where each property is associated with one of three scenarios reflecting the progressive, size-biased extinction typical of vertebrate communities: 1) elephant (~3000 kg) + impala (~70 kg) + dik-dik (~5 kg); 2) impala + dik-dik; or 3) dik-dik only. Using a series of semi-permeable, electrified fences, my research group and I are simulating the above extinction scenarios to address how large mammalian herbivores influence the abundance and distribution of Acacia trees, critical determinants of savanna fire frequency, nutrient cycles, and biodiversity. Specifically, we are working to answer the following questions: 1) How do extinctions of large mammalian herbivores change pollination of savanna trees?; 2) How do impacts of large mammalian herbivores on seed production, germination, and recruitment of savanna trees influence population growth of trees?; and 3) How important are large mammalian herbivores in driving population growth of trees, relative to variation in abiotic factors (e.g., rainfall)? To address the first two questions, my research group and I are combining field experiments with spatial statistics and matrix models. To address the third question, we are "ground truthing" projections from our matrix models across a five-fold gradient in rainfall in central Kenya. Thus, my research group and I will shed light on understanding the ramifications of extinctions for ecosystems. Moreover, through a combination of field experiments, long-term observations, and statistical modeling, we will develop and refine tools that predict the consequences of extinction for plant populations and communities.