Assessing the role of the hydrographic network structure and connectivity on the South American freshwater fish diversity

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Freshwater ecosystems are considered biodiversity hotspots given that they cover only a small fraction of the Earth’s surface yet harbouring a large number of species. A the same time, freshwater species populations have been rapidly declining over the past decades. To slow down or even revert the negative trend, a solid baseline regarding the current status of freshwater biodiversity is urgently required, against which the changes can be compared to. In this regard, spatial freshwater biodiversity science is at the forefront to deliver new information regarding species distributions and for area-based conservation planning. The most unique feature of freshwater ecosystems is the longitudinal connectivity of water bodies, yet is it simultaneously the most prominently neglected feature in freshwater biodiversity analyses. In the proposed project we will address this shortcoming by employing latest graph-theory and species distribution modelling approaches to better understand the species and functional diversity patterns of the South American freshwater fish fauna. Taken together, the South American fish fauna comprises ca. 1/3 of the global fish species, thus serving as an ideal and representative study case. Specifically, we will (i) explore the spatial patterns of the hydrographic network structure across the continent to assess how the water bodies are distributed, and how they are connected. This information will be used in (ii) graph-learning distribution models that capitalize on the spatial network structure, and together with an extensive database of geographic fish records, will yield species diversity estimates across South America. Finally, we will (iii) link up functional trait information with the species distribution estimates to gain insights into spatial functional diversity patterns across South America. The project has the high potential to yield novel insights into spatial freshwater biodiversity patterns across a continental fish fauna in evaluating the role of the underlying network structure on fish diversity estimates. Given the large spatial gradient of the analyses, the results are expected to offer highly generalizable insights of the diversity patterns of a continental freshwater fish fauna, and to yield a cornerstone for area-based information conservation measures addressing the network connectivity structure.