Secondary dispersal moves a forest herb on scales demonstrably relevant to germination and survival

Background/Question/Methods

Seed dispersal is often hierarchical, with different mechanisms successively moving seeds at different spatial scales.  It is unclear, however, whether secondary movement actually contributes to fitness of the plant.  We compare secondary dispersal and environmental heterogeneity in a fleshy fruited forest herb, Podophyllum peltatum, in long established deciduous forests of southeast Ohio, USA.  We experimentally planted seeds and monitored seedling emergence and survival to test demographic responsiveness to microenvironmental variation.  Adjacent-plot surveys were used to characterize spatial distribution of microenvironmental variables at three landscape postions.

Results/Conclusions

Seed planting experiments showed that Podophyllum germination and survival are significantly influenced by microsite slope, litter cover, and shrub shading.  Adjacent-plot surveys showed greater litter on slopes than in ravines or ridge tops.  Litter cover is spatially autocorrelated at scales of 30-50 cm, slope at scales of 0 – 120 cm, and shrub cover on scales of 0 – 40 cm.  These scales are easily within the observed secondary dispersal range of 1.3 meters caused by white footed mice (Peromyscus leucopus) and rain-splash.  We conclude that secondary dispersal can potentially influence the fitness of Podophyllum in this plant community.  Thus, aspects of fruit phenology and physiology influencing secondary movement are potentially products of natural selection.