Fauna de aranhas (Arachnida, Araneae) em diferentes estágios do cultivo do arroz irrigado em Cachoeirinha, RS, Brasil

Abstract

, 17 samples were taken, distributed in three periods: before seeding, during the development of the rice plants and after the harvest. Samples were done in the morning using sweeping nets (35 cm diameter), 50 sweeps in each of four randomly chosen transects. A total of 918 spiders were sampled, distributed in 14 families, mostly Araneidae, Anyphaenidae, Oxyopidae and Tetragnathidae. Among the adults, 38 morphospecies were found, the most abundant were Alpaida veniliae (Keyserling, 1865), Tetragnatha nitens (Audouin, 1826), Ashtabula sp.1 and Tetragnatha aff. jaculator, the four together comprising more than 45% of the adult specimens. Of the species richness estimators used, Chao 1 was closer to the observed richness; 87,4% of the potentially present species were effectively sampled. Both abundance and species richness showed an increasing trend, accompanying rice development (and thus increasing habitat complexity), with a stern decrease after harvesting. A constant colonization of the habitat is thus postulated, also given the high number of young spiders found at all times. There were no significant correlations between climatic factors (temperature and rainfall) and neither abundance nor species richness, except a positive one between rainfall and richness. Among the functional groups, ambushing hunters dominated, followed by orb-web builders. An analysis of similarity (ANOSIM) found significant differences among the fauna of the three evaluated periods. Thus, system disturbance, in the form of rice sowing and harvesting, brutally altering environmental structure, leads to strong spider diversity changes both in terms of species richness and species composition. The results suggest biodiversity studies in agroecosystems can help us understand not only applied but also basic problems.

Factors influencing the appearance of spider (Araneae) and beetle (Coleoptera) assemblages in nests of great reed warbler Acrocephalus arundinaceus

“…The abundance of spider and beetle assemblages did not show a significant relationship with the amount of precipitation (spiders: Spearman, rho 38 = 0.26, P = 0.1148; beetles: rho 38 = 0.09, P = 0.5657). Contrary to our results, other investigations in which spiders (Carrel 2001;Rodrigues et al 2008) and beetles (Orozco & Perez 2008;Grimbacher & Stork 2009) were studied found that the amount of precipitation influenced their abundance. The species richness of spider assemblages differed significantly between the three groups of nests (Student's t-test, t 2 = 5.00, P = 0.0377), while in the case of beetle assemblages the difference in species richness was not significant (t 2 = 2.60, P = 0.1217).…”

Soil invertebrates in southern Brazilian Araucaria forest - grassland mosaic: differences between disturbed and undisturbed areas

“…Seasonal variation on soil use in agricultural areas, e.g. before and after crop planting, can also affect invertebrates composition (RODRIGUES et al, 2008).…”

Spider community responds to litter complexity: insights from a small-scale experiment in an exotic pine stand

“…Specifically in South Brazil, some attempts were done in order to compare spider diversity patterns between agroecosystems and adjacent native ecosystems, such as the studies of Baldissera et al (2008) in tree plantations, including pine, and native Araucaria forest, Rodrigues et al (2009) in rice field, grassland and native forest, and Rodrigues et al (2010) in Eucalyptus plantations and natural grasslands. Other studies in agroecosystems in South Brazil describe spider assemblages, for example, in olive groves (Ricalde et al, 2016), corn plantations (Da Silva et al, 2014), citrus groves (Ott et al, 2007) and irrigated rice (Rodrigues et al, 2008). Here we also expect to contribute with a very first view of the ground spider assemblages inhabiting pine plantations in the state of Rio Grande do Sul.…”