Dissertation Research: Symbiont-mediated niche expansion and partitioning in a native grass-fungal endophyte symbiosis

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A key area of interest to ecologists is why a species occur in a particular range of environments, often called the species niche. Researcher have typically investigated how abiotic limitation of an organism (e.g. thermal tolerance) as well as negative species interactions (e.g. competition and predation) impact where organisms can successfully persist. While this work has proved invaluable, the effect of equally important and widespread positive species interactions on species niches has been virtually ignored. The PIs' research investigates the question: How participation in mutualism (a positive interaction in which all partners benefit) affects the niche of an organism? They examine this question in the association between endophytic fungi (fungi that lives inside plants) and a native grass, Chinook brome (Bromus laevipes). Models based on their endophyte occurrence data from ~100 populations of the grass and climate data strongly suggest that endophytes expand the niche of the grass (i.e. the grass can persist in habitats that would be untenable in the absence of the mutualistic partner). With NSF funding, the PIs will test this result by planting experimental gardens throughout California. Within each garden, they will plant Chinook brome with and without endophyte from 12 populations and measure plant performance (e.g. stem/leaf/seed production), phenology (e.g. flowering/dormancy timing), and herbivore damage. This research will not only elucidate conceptual questions in ecology (e.g. species distributions and diversity, community assembly, and speciation) by incorporating positive interactions into niche theory, but it will also inform applied fields (e.g. agricultural and conservation activities). Although fungal endophytes live inside all plant species examined, we know little about their ecology or evolution in most cases. Given the large impact of endophytes on plant success in different environments, the information about endophytes garnered from this research can help make conservation, restoration, agriculture, or development decisions.