Research

A major goal of community ecology is understanding the processes responsible for generating biodiversity patterns. In stream ecosystems, system specific frameworks have dominated research describing biodiversity change along river networks. However, support for these frameworks has been mixed and these frameworks have placed less emphasis on general mechanisms driving biodiversity. Here, we apply the Theory of Ecological Communities (TEC) framework to focus explicitly on core ecological processes structuring communities. Using a case study of stream invertebrates from alpine lake-stream networks, we tested the generality of stream and the TEC frameworks. Overall, we found support that biodiversity in lake-stream networks is structured along the river network, similar to well-studied streams, but lakes modify aspects of community structure. Despite support for the predicted biodiversity patterns, the mechanistic reasons hypothesized to structure biodiversity were only partially supported. Local diversity was structured by niche selection and ecological drift, where beta-diversity was influenced by dispersal and niche selection. By combining stream ecology frameworks with the TEC, we were able to mechanistically determine why data did and did not conform to predictions from stream ecology frameworks.

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Spatial and environmental heterogeneity have been shown to enhance predator-prey persistence. Theory predicts that aspects of spatial and environmental heterogeneity influence predator-prey persistence through a variety of mechanisms such as statistical stabilization, colonization-extinction dynamics, and trophic interactions. However, comparative tests and syntheses of the multiple factors and mechanisms across different spatial networks are needed to understand whether predictions are robust across spatial systems, environmental variation, and predator-prey identities. Here, we synthesized data from protist predator-prey microcosm experiments differing the productivity, patterns of spatial network connectivity, and metacommunity size. Our analysis focused on how these spatial, environmental, and biotic factors influenced predator-prey persistence, where persistence was measured through extinction times and occupancy. We found that prey time to extinction was better explained by productivity and spatial factors than predator time to extinction. As predicted by theory, metacommunity size and productivity had positive effects on prey occupancy and contrary to predictions, connectivity negatively influenced prey occupancy. For predators, metacommunity size and connectivity had positive effects on predator occupancy, and productivity showed a hump-shaped relationship with predator occupancy. Further, trophic interactions drove variation in spatial occupancy patterns, where the strength and direction of predator-prey occupancy relationships varied among productivity levels and predator-prey combinations due to differences in the importance of top-down and bottom-up effects. Taken together, these results highlight that spatial network structure has a complex, spatially contingent relationship with predator-prey dynamics and mechanisms have detectable and important roles across a range of spatial networks and conditions.

Alpine ecosystems are host to high biodiversity, however these ecosystems are disproportionately affected by climate change. Changing precipitation regimes and the reduction of glaciers and permanent snow together are leading to changes in hydrology and the spatial habitat structure of aquatic ecosystems. Communities of cold adapted aquatic organisms are under threat and characterizing their distributions, physiological responses, and genetic diversity remains a priority to understand their responses to climate change. This project is a large collaborative effort focusing on the meltwater stonefly (Lendia: Plecoptera) throughout the Western USA. Collaborators include Scott Hotaling (UW), Lusha Tronstad (UW), Joe Giersch, and more!

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The sand dunes found on coastal shores and barrier islands are important for protecting inland areas from wind and wave action. This study explored the processes that shape the foredunes, the youngest set of dunes where sediments are deposited by winds blowing up from the beach. Our results suggest that the vegetative community is strongly associated with distance from the shore, where abiotic conditions are harshest closest to the ocean and gradually reduced moving toward the interior of the island. This deterministic community pattern appears to be maintained by the vegetation’s ability to regenerate through time, especially in response to disturbances after heavy wind and wave action. A germination experiment revealed strong differences among the germination rates of different species and the effects of salinity on species-specific germination rates. High rates of germination might be beneficial in colonizing open habitats following storms, where high salinity conditions are especially present. Understanding the patterns that shape vegetative community diversity should help guide restoration management in coastal dune systems and shed light on the importance of individual species and their function within the coastal ecosystem.

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