Habitat fragmentation alters post-dispersal more than pre-dispersal seed predation through edge effects

In addition to causing loss of biodiversity, habitat fragmentation can
alter species interactions. Relative to well-studied effects of
fragmentation on mutualistic interactions like pollination, effects on
antagonistic interactions remain poorly understood. One such interaction,
seed predation, may be particularly important because it can alter plant
demographics and trigger cascading changes to both plant and seed predator
communities. Previous studies have failed to find consistent effects of
fragmentation on seed predation, possibly because seed predation occurs at
two distinct stages relative to seed dispersal (pre- and post-dispersal).
Working within a large-scale fragmentation experiment, we tested effects
of three consequences of fragmentation – edge-to-area ratio, distance to
edge, and connectivity (via habitat corridors) - for pre-dispersal seed
predation and post-dispersal seed removal of eight plant species of
conservation interest. We found that fragmentation effects, especially
distance to edge, were more likely significant for post-dispersal seed
removal (assumed to positively correlate with seed predation) than for
pre-dispersal seed predation, although the significant patterns differed
across species. Post-dispersal seed predation declined sharply with seed
mass and this decline was greater at the patch edge. This led to larger
seeded species having less predation nearest to the edge compared to patch
interiors. This experiment highlights how fragmentation can alter seed
predation by generating edge effects and how species traits can predict
consequences across a community.