The effects of fragmentation on fluctuating asymmetry in passerine birds of Brazilian tropical forests.
Fluctuating asymmetry (FA) refers to the difference between the right and left sides in characters that should otherwise be bilaterally symmetrical, but whose expression is affected by epigenetic stress during development. Forest fragmentation may promote an increase in FA in isolated populations, by either genetic or environmental stress. FA may function as a biomonitor index in conservation biology if increased levels were observed in populations from fragmented habitats. This study tested the hypothesis that FA is higher in birds from small tropical forest patches than in those from large forest tracts. Measurements were made of wing and tarsus FA on mist-netted birds from seven fragments and seven continuous areas from south-eastern Atlantic rain forest in Brazil. FA comparisons were made between fragments and control groups for the whole community, for individual foraging guilds and for the six most abundant species. Wing and tarsus FA were significantly greater in fragments than continuous areas for the whole community and were both negatively correlated with forest fragment size. Differences in FA varied among foraging guilds, being more evident for insectivorous species, especially those feeding in or near the understorey. FA levels increased significantly in forest fragments in at least one trait for five of the six most abundant species. There was no correlation between tarsus and wing asymmetries for the individuals of any species nor any difference between the degree of asymmetries of these characters. It is suggested that FA is a useful tool to assess the effects of fragmentation on forest birds, and may be applied in monitoring neotropical birds. FA indices might be profitably developed, particularly in species most threatened by fragmentation effects and when investigated in different morphological characters.