Ecologia trófica em matrizes agrícolas: uso da ferramenta isotópica para conservação de aves em ambientes antrópicos

Abstract

Information on the consumption of food items from plants of C3 and C4 photosynthetic cycle by a bird community can help determine the potential resilience of forest remnants in agricultural landscapes. This study assessed the diet composition of bird communities in forest fragments embedded in the agricultural landscape of the Corumbataí River basin, São Paulo State, Brazil, using stable isotopes. Eight forest fragments were selected based on their ages, being four classified as “old” (33 and 49 years of age) and four “young” (3 to 11 years of age), arranged in equal proportion in sample units (16 km2), with at least 70% of occupation by the matrix (pasture or sugarcane) and 10% of forest. We performed 12 repetitions in each remnant, totaling 96 sampling. A sequence of five ornithological mist nets (32 mm mesh, 12 m x 2.8 m) was allocated in the nuclear area of each remnant, remaining open for a continuous period of four hours, in the early morning hours. The nets were inspected every 30 minutes. Feather samples were collected for isotopic analysis. We analyzed isotopically 33 species. The percentage of C3 found in individuals of 11 species was related to landscape metrics (percentage of sugarcane and pasture and percentage of forest or nuclear area, mean annual forest change rate, forest change curvature profile and average age). We identified 81 species belonging to 27 families in 979 catches. The most frequently captured species were B. hypoleucus (84.38%), A. galeata (83.33%) and P. mystaceus (71.88%). There was no statistical difference for predominance between the communities in pasture and sugarcane or between old and young remnants. The similarity between the communities in pasture and sugarcane matrices was 50.62%, and 48.15% comparing old and young forest remnants. The isotope analysis of 33 species showed differences in the use of plant resources of C3 and C4 photosynthetic cycle. A total of 78.79% of species had a diet average over 70% of its food consumption solely based on C3 plants, 21.21% consumed C3 and C4 and no species showed predominant consumption of C4 plants. Individual analysis, however, showed that T. fuliginosus and B. flaveolus predominantly consumed C4 plants. Among the 11 species studied, six (A. galeata, A. flavirostris, B. flaveolus, L. euleri, T. coronatus and T. leucomelas) showed a relationship with the landscape variables tested. Diet composition of species was mainly affected by the remnant average age, and results were different regarding the type and ratio of the landscape matrix. Although the fragments sampled are in advanced stage of degradation, the results corroborate the need to preserve these remnants to maintain biodiversity of birds.