Secondary dispersal of deciduous forest herb seeds by rodents in southeastern Ohio

Background/Question/Methods

Seeds of many plants are dispersed by more than one vector in successive stages, which potentially gives them an advantage in heterogeneous environments. Forest herbs are often initially dispersed when vertebrates consume the fruits and defecate the seeds. White-footed mice (Peromyscus leucopus), a species known to cache seeds for later consumption, have been found to remove these seeds from frugivore feces. To determine if the secondary dispersal by rodents contributes additional fitness benefits, we tracked scatter-hoarded seeds and evaluated the microsite quality of seed-caches. We radioactively labeled the seeds of five forest herb species native to southeast Ohio and tracked their movement in forest sites in the late summer and fall of 2019. Environmental specificity was tested by experimentally planting forest herb seeds in a variety of microsite conditions. The environmental features of microsites where seeds germinated were compared to seed cache microsites in order to gauge the effectiveness of Peromyscus leucopus as seed dispersers.

Results/Conclusions

Results suggest that aspects of secondary seed dispersal by scatter-hoarding rodents provide fitness benefits to forest herbs. We were able to locate 58 seed caches over the course of two trials. Seeds moved a median distance of 5.6 meters in individual dispersal events but extreme distances of 15 meters suggest multiple movement steps. Cache distributions expanded at a constant rate consistent with a diffusive process of seed recovery and re-caching. Environmental differences between randomly selected points and seed cache microsites suggest that cache site selection is nonrandom. Higher germination rates were observed in seeds that were shallowly buried under leaf litter or soil compared to seeds that were not covered by either substrate, suggesting that seeds dispersed into caches have a higher likelihood of reproductive success. Germination was also influenced by coarse woody debris, vegetation, microtopography, soil moisture, canopy cover, and tree proximity. Contrary to similar studies, rodents showed a greater preference for smaller seeds and cached them more frequently and at greater distances, suggesting that the fitness benefits associated with dispersal by scatter-hoarding rodents may vary among plant species. Seed caching behavior also varied by season—caches persisted a shorter time in late summer compared to in the fall, suggesting that a plant’s fruiting phenology could impact the dispersal services provided.