The relative roles of habitat heterogeneity and disturbance in drosophilid assemblages (Diptera, Drosophilidae) in the Cerrado

The Brazilian Cerrado, a vegetation mosaic considered to be a unique savannah hotspot, contains a great diversity of insects. It is uncertain how communities of insects in the Cerrado respond, at local scale, to the strong heterogeneity of the biome or to the increasing levels of anthropogenic disturbance. This study examines the relative importance of habitat heterogeneity and human disturbance for the structure of drosophilid assemblages in this biome. Our results are based on standardised monthly sampling at 25 sites (3 conserved forests, 4 disturbed forests, 8 conserved savannahs, and 10 disturbed savannahs) throughout 1year. The assemblage compositions differed across habitats. The conserved forests had a singular drosophilid assemblage characterised by typical narrow-ranging neotropical species. Assemblages from savannahs and disturbed forests contained more exotic species than those from conserved forests. The assemblages of disturbed forests were more similar to those of the savannahs than to those of the conserved forests. Savannah assemblages did not differ from each other; these assemblages shared a great number of both exotic and neotropical species widespread in neotropical regions. At the reserve scale, the strong natural heterogeneity of the Cerrado is the primary factor impacting the structure of drosophilid assemblages. Nevertheless, disturbance explained the differences in assemblage structure between the conserved and disturbed forests. Even low disturbance levels in forests could cause a decrease in heterogeneity and begin to impoverish these environments, leading to the biotic homogenisation of this currently rich biome.