Habitat fragmentation and corridor connectivity impact plant populations through complex influences on plant-animal interactions

Background/Question/Methods

Landscape corridors – strips of habitat that connect otherwise isolated habitat fragments – are a popular management technique used to mitigate negative effects of habitat fragmentation.  Corridors have been shown to promote movement of individuals, plant-animal interactions, and community diversity.  These findings remain disconnected, however, because we know very little about how corridors impact populations.  We used the world’s largest and best replicated corridor experiment (n=8 ~50 ha landscapes) to assess how habitat fragmentation and corridors influence plant populations through influence on fecundity.  Within these landscapes, we established founder populations consisting of hundreds of individuals, for each of five plant species.  We then used structural equation modeling to evaluate how corridors and habitat fragmentation influence plant fecundity (seed production) through impacts on four types of plant-animal interactions.

Results/Conclusions

Impacts of habitat fragmentation and connectivity on plant fecundity, and the mechanisms (i.e., plant-animal interactions) by which these effects manifested were highly complex and variable across species.  Corridor connectivity influenced fecundity in only one species, through influence on rates of pre-dispersal seed predation.  Connectivity further influenced levels of herbivory in two species, but not greatly enough to impact fecundity.  Fragment edge-to-area ratio, which is greater in patches with corridors, influenced fecundity in one species by an impact on pre-dispersal seed predation; we observed additional influences on flower production, plant size, and levels of herbivory.  The most consistent effect (4 of 5 species) we observed was an influence of edges – a consequence of habitat fragmentation and corridor implementation.  Edge effects always operated indirectly, through influence on fecundity due to modifications to plant size (4 of 5 species), flower production (4 of 5 species), or levels of herbivory (3 of 5 species).  Our models provided robust predictions of plant fecundity (r² = 0.43-0.68), but much of this variation was explained by levels of floral production and rates of pollination, each of which were poorly predicted by fragmentation and connectivity.  These findings illustrate how corridors and fragmentation can impact plant populations through indirect influence on a variety of plant-animal interactions, yet the influence of corridor and fragmentation effects on plant fecundity is of lesser magnitude than other ecological influences.