Fauna epígea em fragmento de mata nativa e área agrícola no município de Doutor Maurício Cardoso/RS

Abstract

The invertebrate fauna performs important functions in the dynamics of process related to soil fertility and structure. Biologically mediated processes are fundamental for terrestrial ecosystems maintenance. Soil fauna is, at the same time, important for and the result of soil quality. Various factors, natural and/or anthropic, might modify the abundance and diversity of epigeic fauna. Conversion of native areas for agriculture represents a means of ecosystem modification that could affect soil fauna. This study aimed to survey soil fauna in the rural area of Doutor Maurício Cardoso county, Rio Grande do Sul state, Brazil. Individual of the epigeic fauna were collected using Provid pitfall traps from three distinct areas (native forest fragment, an agricultural area, and forest-agriculture edge area), in three different periods (04/10, 06/04 and 08/20/2016). From the samplings, 14,335 individuals were collected, belonging to 16 groups. In the native forest, relative frequencies of the groups were Collembola (62.4%) > Acari (12.1%) > Hymenoptera (8.5%) > Coleoptera (5.9%) > Diptera (4.2%) > Araneae (3.7%) > others. During the first sampling, Coleoptera was the most abundant group (33%); on the second and third samplings, its frequency was reduced (2.4- 2.7%). Lower frequency (26.3%) was observed for Collembola on the first sampling, which increased on the second and third samplings (53-59%); frequencies of Araneae, Hymenoptera and Acari demonstrated few variations between sampling periods in the forest area. In the forest-agriculture edge, a predominance of Collembola (72%), Hymenoptera (9.9%) and Acari (8.5%) was observed. Collembola prevalence was due to their expressive increase at the third sampling (82%); Hymenoptera represented 36.5% of the individuals on the first sampling, but only 5% in the third sampling; analogously, Acari frequency diminished from 15.7% on the first sampling to 7.3% on the third sampling, and similar profile was observed for Araneae. In the agriculture area, Collembola represented 59.6% of the collected individuals, owing to its increased activity at the third sampling; Acari (17.3%), Araneae (6.3%, Diptera (4.8%), Hymenoptera (4.8%) and Coleoptera (4.3%) were the representative groups. Shannon diversity indices (H) were similar in the first sampling, and the agriculture area displayed the higher values; similar behavior was observed in the second sampling. However, H indices in the third sampling were higher in the forest area, with reductions in the agriculture and forest- agriculture edge, possible due to the explosive increase on Collembola population in these later areas. Simpson dominance indices (D) obtained in the first and second samplings indicated lower values in the agriculture area; in all areas, an increasing trend on D values were observed from the first to the third sampling. Total D-indices indicated lower dominance in the forest area. Pielou evenness indices suggest higher homogeneity in the agriculture area during the first and second samplings. In the forest area, Pielou indices were relatively stable over the sampling periods, with higher total values than the other two areas, indicating a higher uniformity. The forest area was more stable in terms of abundance, relative frequency, diversity, dominance and evenness, while soil management and seasonality caused greater variations in the agricultural and forest-agriculture areas.