The demographic role of soil seed banks. II. Investigations of the fate of experimental seeds of the desert mustard Lesquerella fendleri

Abstract

1. Although poorly studied and understood, the post-dispersal movements and fates of seeds may affect critically the subsequent structure of plant communities, particularly in desert ecosystems where seeds can be the most abundant or only viable form of many plant species. We investigated the fate of experimental seeds of the desert mustard Lesquerella fendleri by examining seed dispersal and predation, and by quantifying the proportion of seeds that germinated and survived as seedlings in three different microsites within a New Mexico desert shrubland. 2. We found very limited seed dispersal but strong density-dependent seed predation by rodents. There was a significant and consistent microsite effect in the proportion of soil seeds germinating and seedlings surviving to the end of the experiments. We did not find a consistent micro site effect for soil seed persistence, but did find a positive correlation between soft seed persistence and soil seed germination. Overall, these results indicate that seed predation may strongly affect the distribution of the seed bank, and that the abiotic environment may largely determine the extent to which soil seed populations in turn affect the distribution of emerging surface plants. 3. We present a seed fate model that synthesizes the results of the present and previous empirical investigations of the Lesquerella study system. This diagram illustrates how interactions among the abiotic environment, microsite variation and seed genotypes can determine which soil seeds successfully germinate and establish into the surface plant population. We suggest that the demography of desert surface plant populations may depend more on the time between seed inputs and the longevity of these seeds in the soft than on the amount of seeds produced at any one point in time and space.