Connectivity from a different perspective: comparing seed dispersal kernels in connected vs. unfragmented landscapes.

Habitat fragmentation can create significant impediments to dispersal.
A technique to increase dispersal between otherwise isolated fragments
is the use of corridors. Although previous studies have compared
dispersal between connected fragments to dispersal between unconnected
fragments, it remains unknown how dispersal between fragments
connected by a corridor compares to dispersal in unfragmented
landscapes. To assess the extent to which corridors can restore
dispersal in fragmented landscapes to levels observed in unfragmented
landscapes, we employed a stable-isotope marking technique to track
seeds within four unfragmented landscapes and eight experimental
landscapes with fragments connected by corridors. We studied two wind-
and two bird-dispersed plant species, because previous community-based
research showed that dispersal mode explains how connectivity effects
vary among species. We constructed dispersal kernels for these species
in unfragmented landscapes and connected fragments by marking seeds in
the center of each landscape with 15N and then recovering marked seeds
in seed traps at distances up to 200 m. For the two wind-dispersed
plants, seed dispersal kernels were similar in unfragmented landscapes
and connected fragments. In contrast, dispersal kernels of
bird-dispersed seeds were both affected by fragmentation and differed
in the direction of the impact: Morella cerifera experienced more and
Rhus copallina experienced less long-distance dispersal in
unfragmented than in connected landscapes. These results show that
corridors can facilitate dispersal probabilities comparable to those
observed in unfragmented landscapes. Although dispersal mode may
provide useful broad predictions, we acknowledge that similar species
may respond uniquely due to factors such as seasonality and disperser
behavior. Our results further indicate that prior work has likely
underestimated dispersal distances of wind-dispersed plants and that
factors altering long-distance dispersal may have a greater impact on
the spread of species than previously thought.