Pulsed Resources and Consumer Communities in Terrestrial Systems

Seed Survivorship & Seedling Establishment

In deciduous and coniferous forests dominated by mast-producing trees, such as oaks, consumers are confronted with the sporadic production of abundant resources. Mast-consuming animals, such as the white-footed mouse (Peromyscus leucopus) and eastern chipmunk (Tamias striatus), rely on these pulsed resources.

Seed Survivorship & Seedling Establishment

Not only do tree seeds have an important bottom-up effect on mice, but also mice have strong top-down effects on seed survival and seedling establishment. Previous studies conducted in old fields adjacent to deciduous forest showed that the survival of experimentally introduced seeds was strongly negatively correlated with mouse abundance.

More recently, we (Schnurr et al. 2004) have assessed whether temporal and spatial variation in mouse abundance affects seed survival and subsequent seedling establishment. We found that the distribution and activity of a guild of small mammals was predictable on the basis of the distribution of canopy trees in neighborhoods (ca 100-200 m2 areas) that represent both individual adult tree canopies and small-mammal home ranges. Granivorous small mammals distribution, in turn, was a good predictor of the intensity of predation on experimentally introduced seeds.

Neighborhoods in which seed predation was lowest were characterized by the highest natural rates of seedling recruitment. If the seedling recruitment signal persists into the sapling and adult tree stages, then canopy trees would appear to be influencing their own neighborhood-specific population dynamics indirectly via their impacts on seed predators.

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