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

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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.