Abstract:
In savannas across the planet, encroaching woody plants are altering ecosystem
functions and reshaping communities. Seed predation by rodents may serve to
slow the encroachment of woody plants in grasslands and savannas. Our goals for
this study were to determine if rodents in an African savanna selectively removed
seeds of an encroaching plant and if foraging activity was influenced by the local
vegetation structure or by the landscape context. From trials with two species of
seeds (encroacher = Dichrostachys cinerea, non-encroaching overstory tree = Senegalia
nigrescens) at 64 seed stations, we recorded 1,065 foraging events by seven
species of granivorous rodents. We found a strong positive relationship between
rodent activity and the number of seeds removed during trials. Foraging events were
dominated by rodent seed predators, with <10.6% of events involving a rodent
with the potential for secondary dispersal. Rodents selectively removed the seeds
of the encroaching species, removing 32.6% more D. cinerea seeds compared to
S. nigrescens. Additionally, rodent activity and the number of seeds removed increased
at sites with more grass biomass. Our results suggest a potential mechanistic role for
rodents in mitigating the spread of woody plants in grass dominated savannas.
