EAGER: Global assessment of the causes and consequences of commonness and rarity in freshwaters

人类活动通过资源过度开发、生境改变和引进非本地物种，导致全球生物多样性下降。当稀有物种消失时，社区的功能就会下降，为人类提供的服务也会贬值，这是一个环境和社会经济问题。虽然生物多样性的丧失是全球性的，影响到所有生态系统，但淡水生物多样性受到的威胁比陆地生境高得多。因此，迫切需要更好地了解淡水中稀有的原因和程度。物种稀有度可以使用物种丰度分布（SAD）进行评估，这是一种衡量常见和稀有物种相对丰度的方法。虽然SAD已经研究了70多年，但对决定丰度不平等模式的基本机制知之甚少。这项研究将通过制定一个新的框架来弥补这一知识差距，该框架将预测撒哈拉以南非洲荒漠化在淡水生境中的反应，沿着环境和空间梯度。这项研究还将调查撒哈拉沙漠地区如何影响区域生物多样性。最后，该研究将通过阐明保护目标物种稀有的原因，为流域管理和生物多样性保护的决策提供信息。本项目还将为一名博士后、一名研究生和几名本科生提供研究培训。本项目制定了具体的假设，预测SAD变异性对生态位和扩散相关机制的响应，作为规模、体型和连通性的函数。这些假设将通过美国和外国机构从流动和静止的沃茨水域收集的淡水藻类、无脊椎动物和鱼类的全球数据来检验。然后，它将确定如何，反过来，SAD约束β多样性的模式，区域生物多样性的一个关键组成部分，采用零模型的方法。具有保护或环境重要性的群落和物种群的SAD将与适当的模型相匹配。这些模型的参数的变化将进行统计分析，沿着梯度的水化学，气候，土地利用，纬度，经度和海拔高度，跨尺度，栖息地和生物群。实施拟议的框架将导致更好地整合生态系统和保护。

Human activity has caused a decline in global biodiversity through resource overexploitation, habitat modification, and introduction of non-native species. When rare species are lost, communities exhibit decreased functionality and provide devalued services to humans, which is an environmental and a socioeconomic problem. Although biodiversity loss is global and affects all ecosystems, biodiversity in freshwaters is threatened by much higher extinction rates compared to terrestrial habitats. Therefore, a better understanding of the causes and extent of rarity in freshwaters is urgently needed. Species rarity can be assessed using the species abundance distribution (SAD), which is a measure of the relative abundances of common and rare species. Although the SAD has been investigated for more than 70 years, little is known about the underlying mechanisms that determine the patterns of abundance inequality. The study will address this knowledge gap by developing a novel framework which predicts the response of the SAD in freshwater habitats along environmental and spatial gradients. The study will also investigate how the SAD affects regional biodiversity. Finally, the study will inform decisions for watershed management and biodiversity preservation by elucidating the causes of rarity in species targeted for conservation. This project will also provide research training for one postdoctoral associated, one graduate student and several undergraduate students.This project formulates specific hypotheses, predicting the SAD variability in response to niche and dispersal-related mechanisms as a function of scale, body size, and connectivity. These hypotheses will be tested with global data on freshwater algae, invertebrates, and fish, collected from running and standing waters by US and foreign agencies. Then, it will be determined how, in turn, the SAD constrains the patterns of beta diversity, a key component of regional biodiversity, by employing null model approaches. The SAD of communities and species groups of conservational or environmental importance will be fit with appropriate models. The variability of the parameters of these models will be analyzed statistically along gradients of water chemistry, climate, land use, latitude, longitude, and altitude, and across scales, habitats, and organismal groups. Implementation of the proposed framework would lead to better integration of metacommunity ecology and conservation.