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

人类活动通过过度开发资源、改变生境和引入外来物种导致全球生物多样性下降。当稀有物种消失时，群落的功能会下降，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。尽管生物多样性丧失是全球性的，影响到所有生态系统，但淡水生物多样性受到的灭绝率比陆地生境高得多的威胁。因此，迫切需要更好地了解淡水中稀有的原因和程度。物种丰度分布（SAD）是衡量常见物种和稀有物种相对丰度的一种方法。尽管SAD已经被研究了70多年，但人们对决定富足不平等模式的潜在机制知之甚少。该研究将通过开发一个新的框架来解决这一知识差距，该框架可以沿环境和空间梯度预测淡水栖息地中SAD的响应。该研究还将调查SAD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。该项目提出了具体的假设，预测了生态位和分散相关机制对SAD变异性的响应，作为规模、体型和连通性的函数。这些假设将用全球淡水藻类、无脊椎动物和鱼类的数据进行检验，这些数据是由美国和外国机构从流动水域和静止水域收集的。然后，通过采用零模型方法，确定SAD如何反过来限制区域生物多样性的关键组成部分beta多样性的模式。对保护或环境具有重要意义的群落和物种群的SAD将采用适当的模型进行拟合。这些模型参数的变异性将沿着水化学、气候、土地利用、纬度、经度和海拔的梯度，以及跨尺度、栖息地和生物群体进行统计分析。该框架的实施将使元群落生态与保护更好地结合起来。

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.