CAREER: Drought and metacommunity stability in riverine networks

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The frequency, duration, and severity of droughts is increasing in many regions of the world. Drought can negatively impact riverine ecosystems—particularly if streams that generally flow year-round become intermittent. Climatic droughts can isolate entire portions of the river network, and synchronize fluctuations in abundance of aquatic organisms across large spatial scales. How these isolation and synchronization processes may endanger aquatic species directly, or indirectly by modifying species interactions, remains largely unknown. Here I propose to address this gap by combining long-term monitoring and field experiments in an intermittent river network in Pinnacles National Park, with large-scale modeling of stream biodiversity and hydrology data. This CAREER integrates research and education goals, and will provide students from underrepresented backgrounds with hands-on experience on stream sensor instrumentation, biodiversity sampling, and analysis of time-series data. It will also create an Ecological Drought Collaboratory spanning academic, government, and museum institutions researching drought-related questions.Despite much research on freshwater biodiversity responses to drought, it remains difficult to predict responses at high levels of biological organization (food webs and metacommunities). This is largely because biotic interactions can dampen or amplify impacts of abiotic stress on each species. Moreover, drought may erode the capacity of organisms to disperse and recolonize from other sources (resilience strategists), or to persist locally and bounce back after drying events (resistance strategists). Through a combination of approaches that span spatio-temporal scales and disciplines (metacommunity ecology, stream hydrology, time-series analysis), the investigator will determine the net contribution of drought to metacommunity stability. The specific goals of this project are: (i) understanding the controls of metacommunity stability in streams, with a focus on the relatively understudied mechanisms of drought-driven dispersal limitation and synchrony; (ii) determining to what extent recent climatic droughts, in isolation or in conjunction with human activities, synchronized flow regimes within and across river networks; and (iii) forecasting the vulnerability of U.S. stream invertebrates and fishes to future droughts, considering not only local biotic and abiotic change (temperature and flow) but also network-level shifts in habitat portfolio and connectivity. This work will fill a critical gap in our mechanistic understanding of metacommunity dynamics in dendritic networks, and will help better quantify risk of freshwater biodiversity loss under increasingly-variable climates. Integrated educational objectives targeting undergraduate and graduate students, conservation practitioners, and the public will promote understanding of how biodiversity persists in river networks. This increased understanding should improve conservation outcomes via robust design of environmental flows and habitat restoration actions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.