Edge-mediated patterns of seed removal in experimentally connected and fragmented landscapes

While biological reserves remain central to biodiversity conservation,
the amount of area available for terrestrial reserves may be
inadequate for many taxa. Biodiversity spillover-the promotion of
diversity in matrix areas surrounding reserves-might help address this
shortfall in reserve area. However, the mechanistic underpinning of
spillover remains uninvestigated. Two fundamental processes-seed
dispersal and establishment-might generate plant biodiversity
spillover. Here, we investigate the role of establishment in promoting
spillover by assessing post-dispersal seed predation, a key component
of establishment, in the matrix of a replicated, large-scale habitat
fragmentation experiment, where spillover is elevated around patches
connected by landscape corridors. Our results show that matrix seed
predation may constrain the distance of this spillover effect by
reducing establishment: seed removal was least at the matrix edge and
increased further into the matrix. We found some support for matrix
seed predation underpinning previously reported landscape-level
variation in spillover. Of the three species we investigated, two
showed evidence for elevated seed predation in the matrix surrounding
the unconnected patches around which the lowest levels of spillover
occur. However, seed predation did not explain connectivity-enhanced
spillover, suggesting that seed dispersal likely drives this pattern.
Management activities that increase seed deposition in the matrix may
have beneficial effects via spillover. Our work also illustrates that
matrix-mediated gradients in seed predation may be widespread, but
likely vary depending upon matrix composition and the ecological
system under consideration. In fragmented landscapes, this gradient
could impact the distribution, abundance, and spread of plant species.