Spatial patterns and causes of overwinter seed mortality in Phytolacca americana

To examine the causes of spatial variation in overwinter seed survivorship for an early successional plant, an artificial seed bank study was carried out. The design of the study separated vertebrate and nonvertebrate causes of overwinter seed mortality over three spatial scales. Vertebrate activity reduced seed survivorship more in disturbed than in intact forest, and within disturbed forest seed survival in patch types differed by transect, suggesting that vertebrate foraging behavior varies within the landscape context. Nonvertebrate and abiotic effects also suppressed seed survival within disturbed forest to a small but significant extent more than in intact forest, and transects within the disturbed area varied in their effects on survivorship. A second study examined the short-term spatial patterns of vertebrate predation only and showed transect-level patterns of seed predation that differed from those found in the longer term study. These results illustrate not only large spatial variation in vertebrate predation, but also the potentially important influence of less frequently measured effects of seasonal changes, abiotic conditions, and invertebrate and pathogenic attack on seed survival.