The contribution of vertebrates to the dispersal of mayapple (Podophyllum peltatum)

Background/Question/Methods

Dispersal of seeds allows forest herbs to persist in heterogeneous and dynamic landscapes, especially in landscapes fragmented by human land use. Mayapple (Podophyllum peltatum) is a common Eastern-forest herb which produces vertebrate ingested fruit. Whitetail deer (Odocoileus virginianus) and raccoon (Procyon lotor) are newly documented consumers of mayapple. Due to their purposeful movement around the forest, animals have the ability to place seeds in narrowly defined microsites which potentially promote seedling establishment (“directed dispersal”). In this study we investigated the contribution of whitetail deer and raccoon to the distribution of mayapple in southeastern Ohio and sought to determine the degree to which their dispersal may be directed dispersal. To this end, parallel transects were used to locate 70 dung deposition sites of deer and 70 of raccoon in closed canopy forests for the duration of the mayapple fruiting season. Locations of dung deposition were compared with 1) random points and 2) with rooting points of vegetative and reproductive mayapple plants on the basis of sixteen plant-relevant environmental variables using Principle Coordinate Analysis. The effects of gut passage on mayapple seed germination rates were also determined by feeding fruit to captive deer and raccoon.

Results/Conclusions

Mayapple need microsites that remain moist in order to germinate and form reproductive shoots. Mayapple seeds that dry out for short periods of time have significantly reduced germination rates. In the study area, whitetail deer defecated predominantly in open locations on ridges. These areas tend to be drier than bottoms and lower slopes. Deer also destroy greater than 99% of mayapple seeds consumed. Raccoons destroy 70% of seeds consumed but they distributed the surviving seeds predominantly on the up-slope base of trees on slopes and on terraces. These sites have a greater soil moisture content and greater leaf litter than random locations. Our results suggest that raccoon dispersal of mayapple, although not significantly directed dispersal, does center the distribution of seeds on specific microsites that are favorable for mayapple recruitment. Deer appear to be seed predators of mayapple. The negative impact on the reproductive dispersal of this forest herb is yet another result of a historically high deer population in southeastern Ohio.