Tropical forest loss drives divergent patterns in functional diversity of forest and non-forest birds

Tropical forests have been facing high rates of deforestation
driven by multiple anthropogenic disturbances, with severe consequences for
biodiversity. However, the understanding of such effects on functional
diversity is still limited in tropical regions, especially considering
different ecological groups responses. Here we evaluated the functional
responses of birds to forest loss at the threatened Brazilian Atlantic
forest, considering the complete assemblage, and both forest-dependent and
non-forest-dependent species. Birds were surveyed in 40 forest sites with a
forest cover gradient, located in two regions showing different land use
types. We tested different models to assess the responses of functional
diversity indices to forest loss in these sites. Although functional
diversity did not differ between regions, forest and non-forest birds
showed divergent responses to forest loss. Deforested landscapes presented
an increase in functional richness (SESFRic) and evenness for forest
species and an increase of functional dispersion for non-forest birds.
Additionally, forested landscapes harbour birds presenting lower body mass
and wing length, and non-forest species with lower tarsus length. The
maintenance of some functional metrics through forest loss resulted from a
compensatory dynamic between forest and non-forest birds, indicating that
only evaluating the complete assemblage may mask important idiosyncratic
patterns of different ecological groups. Although non-forest species are
relatively capable to maintain bird functional diversity in deforested
landscapes, forest birds are facing a drastic ongoing collapse in these
sites, representing an alarming signal for the maintenance of forest
ecosystem function.