Do Symbioses Determine Plant Species Abundances? How Endophytic Fungi May Control Rarity, Dominance, and Invasiveness of Grasses

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Species fundamentally vary in their abundance, spanning a range from federally endangered species to severely weedy invaders. Several hypotheses have been proposed to explain this pattern, but none sufficiently account for observed variation. In part, this failure might reflect the fact that microbial symbioses (widespread, mutually beneficial associations between microbes and plants) have been largely ignored. This proposal forges a new direction by evaluating the role of microbial symbioses in governing rarity and invasiveness. Taking advantage of the experimentally tractable symbioses between grasses and microbial endophytes (fungi that live within plant leaves), proposed experiments and demographic models test whether and how symbionts increase host abundance. In grasses, endophytes may improve host resistance to herbivory through the production of alkaloids toxic to insects and mammals and also may enhance host drought tolerance. Comparative experiments on paired rare and common grass species will test predictions that symbionts benefits are greater for common than rare host species and differ between native and non-native hosts, providing the most comprehensive study to date on the ecology of grass-endophyte symbioses. A clearer understanding of endophyte ecology can offer novel strategies for rare plant conservation and invasive plant control (e.g., via endophyte additions or eliminations). Through networks established in both Indiana and Texas, information will be broadly communicated to state agencies, preserve managers, seed companies, and conservation organizations. The work will additionally integrate teaching and research, by training graduate and undergraduate students as well as bringing contemporary research into the classroom.