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Greater Yellowstone Ecosystem Report

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Understanding the effects of individual species on community- and ecosystem-level processes is of critical importance in ecology. Recent work has demonstrated that variation in genetically controlled traits within foundation species can have large implications for ecosystem processes. Identifying these traits and the selective pressures on them is crucial in understanding how ecosystems are structured and how the systems will respond to disturbance. Serotiny, the long-term storage of seeds in the canopy, is thought to be an adaptation to stand replacing fire. Seeds from serotinous plants are released following a fire, and the proportion of serotinous trees determines sapling density following a fire. The effects of serotiny are not limited to the serotinous species, as sapling density is an important determinant of plant community structure and ecosystem processes (including primary productivity and nutrient cycling). Seed predation may select against serotiny, however, no studies have addressed how the relative strengths of selection from fire and seed predation combine to produce the spatial pattern of serotiny on the landscape. Here, we report on an ongoing study of the effects of selection from seed predation in lodgepole pine (Pinus contorta), a serotinous North American conifer. Red squirrels are negatively associated with serotiny at broad geographic scales, and may select against the serotinous trait. This project examined 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 tested whether this correlation was present at landscape scales, whether the fitness of serotinous trees was reduced in the presence of red squirrels, and what factors controlled the density of red squirrels. Preliminary results indicate that serotiny and squirrel density is negatively correlated, but only at low elevations. In the presence of squirrels, we observed significantly lower cone survival in serotinous trees, suggesting reduced fitness. Squirrel density was strongly affected by several measures of forest structure, including species composition, overhead canopy cover, and tree size (mean DBH).