Neotyphodium fungal endophytes are keystone species in temperate grasslands: impacts from population ecology to ecosystem functioning

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Pasture and turfgrasses used throughout North America are mostly non-native species. These grasses routinely escape their human management and invade natural and unmanaged ecosystems where they are widely considered to be significant invasive species. The impact that these grasses have on the ecosystems that they invade is thought to be more significant when those plants are infected with endophytic fungi. Agricultural and turfgrasses are often hosts of systemic symbiotic fungal endophytes which reside in aerial plant parts and are vertically transmitted through the seeds of infected grasses. Theory suggests that the vertically transmitted symbionts must, in some way, enhance the fitness of the host plant if they are to be maintained in the population. Endophyte infection is proposed to benefit their host grasses through increased tolerance to abiotic stress (e.g. drought), enhanced growth and competitive ability, and increased resistance to herbivory due to the production of endophyte-derived alkaloids. Indeed, this last benefit has led many to describe the interaction as a defense mutualism. All of these benefits make endophyte-infected grasses more likely to succeed in invading natural communities and to have greater impact when they do invade such communities. Here I propose to address three important questions for conservation of biodiversity and ecosystem functioning in North American grasslands. First, if endophyte infection is supposed to be so beneficial, why is the infection rate in grasslands often less than 100%? Second, what are the impacts of grass-endophyte invasion for plant and animal biodiversity and ecosystem functioning in invaded grasslands? And third, do the impacts of invasion vary depending on the spatial grain of the invasion? I will use these results to develop a mathematical model of the grass-endophyte interaction that will help us form and test hypotheses in the future.