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Greater Yellowstone Ecosystem Report

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Coevolutionary interactions can have dramatic effects on the structure and function of ecosystems, particularly when spatial structure leads to local adaptation. Here we report on an ongoing study of the interaction between lodgepole pine and its primary pre-dispersal seed predator, the American red squirrel. Lodgepole pine is serotinous, meaning seeds are held in closed cones until released by the heat of a fire. Serotiny has been shown to increase seedling density following stand replacing fire, and can have far-reaching ecosystem- and community-level implications. Red squirrels are negatively associated with serotiny at broad geographic scales, and may select against the serotinous trait. This project aims to examine the correlation between red squirrel density and the frequency of serotiny in lodgepole pine forests and the mechanisms underlying potential selection against serotiny by red squirrels. Specifically, we will determine whether this correlation is present when other factors affecting serotiny (i.e., fire frequency, elevation) are held constant, whether the fitness of serotinous trees is reduced in the presence of red squirrels, and what factors control the density of red squirrels. Preliminary results indicate that serotiny and squirrel density is strongly negatively correlated, but only at low elevations. Serotiny was nearly absent at high elevations, but squirrel density varied as much as at low elevations, suggesting that serotiny does not control squirrel density, but that increasing squirrel density may lead to increasing selection against serotiny.