Bioindicadores ambientais: análises ecológicas de comunidades de insetos e aracnídeos em ecossistemas naturais e agroecossistemas

Abstract

The decrease in the complexity of habitats for agricultural purposes has direct impacts on biodiversity, which can indicate the degree of environmental disturbance through studies of edaphic fauna communities. Insects and arachnids are the target of studies, as they are considered good environmental bioindicators. This study aimed to analyze and compare structures and ecological parameters of insect and arachnid communities in natural ecosystems and agroecosystems in the municipality of Igarapé-Açu, Pará. The experiment was developed at the Experimental Farm of Igarapé-Açu - PA, municipality of Igarapé -Açu, belonging to the Federal Rural University of the Amazon, with monthly sampling from April / 2015 to April / 2017, a total of 34 samples. Two natural areas and five agroecosystems were determined according to the plant structure and size of the areas. Arthropods were sampled using pitfall traps, which were in the area for 7 days before collection. The samples were sent to the laboratory for sorting, morphospection and labeling of insects and arachnids. Using the free software PAST 4.0, the following indices were determined: Jackknife 2 estimator; Menhinick and Margalef wealth; dominance of Simpson and Berger-Parker; Shannon's diversity; equitability J and Evenness by Buzas & Gibson; Fisher alpha diversity; diversity profiles (Rényi series); rarefaction curve and similarity of Sorensen and Morisita. 80,847 adult specimens corresponding to the Acari and Araneae taxa and ten insect orders were sampled. The insect orders Hymenoptera, Coleoptera and Diptera, stood out as the most abundant with 54,139, 15,437 and 2,430 individuals, respectively. Among the arachnids, the Acari showed 7,374 and Araneae 1,036 individuals. The orange (35,919 individuals) and corn (10,140 individuals) agroecosystems showed the highest number of specimens due to the large number of ants (Formicidae) that occurred in the traps in these places. The natural area with up to 10 years of conservation also showed a high number, 9,538 individuals, represented mostly by mites. The taxa that stood out with the highest number of morphospecies were the insect orders Coleoptera (571), Hymenoptera (333) and Diptera (176), and among arachnids, spiders with 102. The abundance and richness of morphospecies indicated that the area may have a high abundance, but its morphospecies richness may be low, especially the orange agroecosystem. Ecological analyzes indicated that the more conserved an environment, the greater its diversity, such as the natural area with more than 30 years of conservation, in addition to agroecosystems that do not have an intense management, for example, the black pepper agroecosystem. The similarities, quantitative and qualitative, showed the clusters of ecosystems and agricultural systems that have similar environmental characteristics, highlighting the pasture, corn and orange agroecosystems as the most degraded. While the area with more than 30 years of conservation and the mango and black pepper agroecosystems, present good resources for the survival of different groups of arthropods.