Avian community and population processes in a dynamic Amazonian landscape: Lessons from 30 years at the Biological Dynamics of Forest Fragments Project

Background/Question/Methods

For decades, researchers have studied fundamental questions of how Amazonian biodiversity is maintained, and whether that diversity can persist as Amazonian forests are increasingly perturbed.  Our approach to addressing these questions has changed, however, as theory and empirical understanding have developed.  The long history of avian research at the Biological Dynamics of Forest Fragments Project, near Manaus, Brazil, reflects these changes.  When the project was developed, in the late 1970s, the focus was informed by island biogeography theory:  how does patch size influence abundance and number of species?  Through the 1990s, landscape dynamics, not just patch size, were increasingly integrated into results as second growth developed in deforested areas.  Now, we consider patches and matrix together, and are beginning to address the differences in not just community composition, but also biological processes, in recovering second growth, as well as in fragments and continuous forest.  Our challenge now is to determine under what conditions remnant patches and developing second growth can support not just the rich diversity of Amazonian rainforest species, but also their population processes and emergent community properties.

Results/Conclusions

In the short term following isolation, standardized sampling of understory birds in 1-, 10-, and 100-ha forest fragments revealed expected area effects on extinction and abundance, but other patterns emerged with longer-term sampling.  Birds differentially recolonized fragments based on treatment of the matrix following deforestation, returning much faster through matrix that was never burned.  These landscape effects mostly disappeared after about 20 years of second growth development.   Now, some 30 years following isolation, we know that many species appear and disappear repeatedly from fragments, although we have identified others that never returned after their in initial extinction in the 1980s.  Thus the species present in fragments are mainly determined by turnover, not by long-term attrition of species.   Birds moving through second growth and using small fragments include young birds probably originating in continuous forest, but some species persist in fragments through local recruitment.  Reduced social organization in fragments and second growth, as revealed by interaction network analysis, is consistent with high transience and with long-term changes in physical structure of fragment vegetation.  Describing these responses, and especially the temporal scale at which they occur, would have been difficult or impossible without long-term sampling.