Beyond the Local Catchment: Influence of Regional Context and Land Use Legacy on Current Stream Fish Diversity in Agricultural Systems

ABSTRACT Land use poses a major threat to global biodiversity, impacting ecosystems across various spatial and temporal scales. Recent studies suggest that past land use changes influence the observed contemporary diversity patterns in stream fish assemblages more strongly than current land use. However, these studies often focus on limited spatial scales, and it remains unclear whether the influence of historical land use holds true when analysing broader regional contexts. In this study, we address how historical changes in local (upland catchment) and regional (broader watershed) land use interactively affect stream fish diversity using fish community data from 366 streams in Brazil, sampled from watersheds with varied agricultural land use histories. We found that local species richness (alpha diversity) was influenced by both current and historical land uses at regional extent, while beta diversity was more influenced by current regional land use than by historical land use. Additionally, we mapped the status of regional watersheds for fish diversity conservation, identifying areas with lower or more recent land use. The results indicate that local catchment land use and fish diversity relationships may not be evident in catchments immersed in heavily modified regional contexts or in regions that have faced long historical land use changes. Our findings highlight the importance of the regional context and past land use legacy for the management and conservation of aquatic ecosystems.