PS 62-46
Influence of second growth and forest fragmentation on the community structure and demography of an Amazonian bird community
Avian diversity in fragmented Amazonian landscapes depends on a balance between extinction and persistence dynamics in cleared and disturbed areas, respectively. Regenerating second growth facilitates bird dispersal within degraded Amazonian landscapes and may tip the balance in favor of persistence in previously depauperate habitat patches. Similarly, in lieu of immigration, persistence dynamics in forest patches and second growth may also depend on population-level survival and growth. Despite the potential ecological value of regenerating second growth to Neotropical birds, few studies have measured differences in bird communities and demography across disturbance gradients in the Amazon. In this study we used point counts and capture methodologies to determine the influence of regenerating forest and fragmentation on avian community structure, survival, and population growth in continuous forest plots, 100 ha forest fragments with adjacent second growth, 100 ha forested islands bounded by water, young (15 year old) second growth, and older (25 year old) second growth plots.
Results/Conclusions
Our results suggest that islands and young second growth had fewer species than continuous forest, fragments surrounded by matrix or older second growth. Among foraging guilds, understory insectivores and obligate-flocking species were depauperate in islands and young second growth. Fragments surrounded by a matrix were surprisingly species rich, suggesting that a permeable matrix may mitigate extinction events associated with a fragmented landscape. Although communities were relativly similar between older second growth and continuous forest, most birds, irrespective of foraging guild, exhibited lower survival and population growth in mature second growth relative to forest fragments and continuous forest. Our findings reinforce that true islands are extinction-driven systems with distinct, depauperate communities. In contrast, succession of bird communities in second growth facilitates recolonization of forest fragments in regenerating landscapes, despite lower survival and population growth, permitting larger fragments to support bird communities similar to continuous forest.