Abstract
Edge effects, driven by human modification of landscapes, can have critical impacts on ecological processes such as species interactions, with cascading impacts on biodiversity as a whole. Characterizing how edges affect vital biotic interactions such as seed dispersal by frugivores is important for better understanding potential mechanisms that drive species coexistence and diversity within a plant community. Here, we investigated how differences between frugivore communities at the forest edge and interior habitats of a diverse tropical rainforest relate to patterns of animal-mediated seed dispersal and early seedling recruitment. We found that the lemur communities across the forest edge-interior gradient in this system showed the highest species richness and variability in body sizes at intermediate distances; the community of birds showed the opposite pattern for species richness. Three large-bodied frugivores, known to be effective dispersers of large seeds, tended to avoid the forest edge. As result, the forest edges received a lower rate of animal-mediated seed dispersal compared to the interior habitats. In addition, we also found that the seeds that were actively dispersed by animals in forest edge habitats were smaller in size than seeds dispersed in the forest interior. This pattern was found despite a similarity in seed size of seasonally fruiting adult trees and shrubs between the two habitats. Despite these differences in dispersal patterns, we did not observe any differences in the rates of seedling recruitment or seed-size distribution of successful recruit species. Our results suggest that a small number of frugivores may act as a potential biotic filter, acting on seed size, for the arrival of certain plant species to edge habitats, but other factors may be more important for driving recruitment patterns, at least in the short term. Further research is needed to better understand the potential long-term impacts of altered dispersal regimes relative to other environmental factors on the successional dynamics of edge communities. Our findings are important for understanding potential ecological drivers of tree community changes in forest edges and have implications for conservation management and restoration of large-seeded tree species in disturbed habitats.
Highlights
Human-induced habitat loss, fragmentation, and degradation of forested habitats around the world have resulted in 70% of the world’s forested area existing within 1 km of a forest edge (Haddad et al, 2015)
We compared how the mean rates of active seed dispersal differed between the two habitat types by performing an linear mixed-effects (LME) regression model, in which we considered the habitat type as a fixed effect and transect as a random effect
The site’s two frugivorous pigeons, A. madagascariensis and T. australis, may avoid edge habitat as they were absent from forest edges and were only observed at a minimum distance of 475 and 1,529 m from the edge, respectively (Figure 1C and Supplementary Table 2)
Summary
Human-induced habitat loss, fragmentation, and degradation of forested habitats around the world have resulted in 70% of the world’s forested area existing within 1 km of a forest edge (Haddad et al, 2015). In forest edges, abiotic factors such as reduced soil moisture or increased sunlight exposure can act as an environmental filter by preventing or favoring the establishment of certain plant species (Kraft et al, 2015) Along with these abiotic factors, changes in ecological processes and species interactions such as seed dispersal by animals (zoochory) can act as a potential filter for plant communities by limiting or increasing seed supply, which will affect the initial template for regeneration and may affect the patterns of species occurrence and diversity in a local community (George and Bazzaz, 1999; Myers and Harms, 2009; Albert et al, 2015). Differences in abundance and composition of frugivores may differ due to avoidance or attraction to habitat or resource characteristics present on the forest edge (Johns and Skorupa, 1987; Gray et al, 2007; Gomes et al, 2008)
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