Small mammals reduce distance-dependence and increase seed predation risk in tropical rainforest fragments

Seed predation and reduced predation risk with distance from conspecific
trees are important influences on tree regeneration in tropical forests.
Shifts in animal communities, such as an increase in rodents and other
small mammals due to forest fragmentation, could alter patterns of seed
predation and affect tree regeneration and community dynamics in forest
fragments. We performed a field experiment on four native rainforest tree
species in the Western Ghats, India, to test whether fragmentation
increases seed predation by mammals and alters the distance-dependence of
seed predation. We monitored seed predation within open and
mammal-exclosure plots, near and far from the canopies of conspecific
trees, in contiguous and fragmented forests. Seed predation of Cullenia
exarillata, Ormosia travancorica, and Syzygium rubicundum was markedly
higher in forest fragments, and more so within open plots than exclosures,
while the predominantly insect-predated Acronychia pedunculata experienced
similar predation in contiguous forests and fragments. Seed predation of
C. exarillata and S. rubicundum was unrelated to distance from conspecific
trees in open plots in both contiguous forests and fragments, in contrast
to exclosures that showed marked near versus far differences in seed
predation. Our findings suggest that by increasing overall seed predation
risk and imposing similar seed predation risk near and far from adults
variably across the tree species, small mammals could alter processes that
shape tree diversity and species composition in fragmented tropical
rainforests.