Seed dispersal is spatially variable depending on plant species composition surrounding a focal patch so that the seed rain reaching a site can potentially vary from nearly monospecific to a complex mix of species. These differences in seed pools may influence emergence as some species can release chemicals that either signal or inhibit germination. In addition, seed predators or pathogens may cause density-dependent changes in seed mortality. Consequently, the composition and density of seed pools may alter patterns of emergence. Because early life stages for plants are often critical to colonization, factors regulating emergence and early survival may have important consequences for population establishment and community diversity. We tested how density and conspecific and heterospecific seed mixtures influenced seedling emergence and survivorship of fifteen perennial species in a restored prairie. For each seed density treatment, we sowed seeds of each species individually or in combination with fourteen heterospecifics and assessed the fractional emergence and survivorship over the growing season.
Results/Conclusions
Five species had higher fractional emergence in the presence of heterospecific than conspecific seed pools and all showed this response during the initial germination period with no difference among seed pools in subsequent sample periods. Conversely, four species had lower fractional emergence in the presence of conspecific than heterospecific seed pools but this differences was only evident in the late in the growing season. One species showed a reversal over the growing season; early in the growing season, higher fractional emergence occurred in the presence of heterospecific seed pools while later in the growing season highest fractional emergence occurred in the presence of conspecific seed pools. These results suggest that seeds from perennial plants are sensitive to the presence of other seeds. While the exact mechanism remains unclear, the fact that most species showed differential responses to variation in seed pools has potential consequences for population dynamics and community diversity.
