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Question:
Does seed dispersal limit seedling recruitment?
Why do we care?
Until not too many years ago, ecological theorists generally made the implicit assumption that seeds arrived at all possible locations for their establishment. In other words, the seed rain was assumed to be infinitely dense and infinitely species-rich. Seed trapping studies quickly solved this misapprehension, illuminating the fact that seeds in fact fall mainly close to the fruiting parent, and that long-distance dispersal is rare. It has rarely been shown, however, that the density and species richness of the seedling community is limited by seed dispersal. In this study, I seek to quantify the strength of that limitation, if any.
Approach:
This is a seed-addition experiment, meaning that I artificially disperse seeds, adding them to one-meter-square plots. The additions took two forms. In the first, I added varying densities of single species of seeds to determine if dispersal limits the density of the seedling community. In the second, I added varying species richnesses (0-8 species) at a constant density to determine if dispersal limits the species richness of the seedling community. I monitor the plots annually, and measure potentially important covariates like light and water availability.
Results:
Among the focal plants, there is a strong signature of dispersal limitation on the density and diversity of seedlings. I expect that the signal of dispersal limitation will fade with time, as the seedlings pass through the successive filters of seedling establishment.
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