Efeito do uso do hábitat sobre a comunidade de Gerromorpha (Heteroptera) em uma área de transição Amazônia-cerrado, Mato Grosso, Brasil

Abstract

The aquatic and semiaquatic bugs (Heteroptera) belong to three different monophyletic infra-orders: Gerromorpha, Nepomorpha and Leptopodomorpha. In Brazil only a few studies on these groups have been carried out, mostly in the state of Minas Gerais. This study aimed to determine land use intensity effect over the aquatic Heteroptera-Gerromorpha community. The study was carried out at Tanguro farm, state of Mato Grosso, in a area of transition between cerrado and tropical rain forest. Samples were collected on May and July in 2006 and 2007 in six streams within three different environments: soybean plantation, pasture and forest. Five families, 19 genera, 36 species and 13 morphospecies of Gerromorpha were collected. Species accumulation curves for each environment did not reach an asymptote, though they showed a clear tendency to stabilization. Therefore, increasing the number of samples probably will set the real species number close to the observed for the whole study area. Although vegetation coverage was significantly different among the three environments (ANOVA, F2,45= 23,72; P < 0,001), the habitat type did not influence the number of Gerromorpha species (ANOVA F3,44= 0,77; P = 0,52). In addition, the two axis of a MDS analysis based on species composition did not discriminate the habitats. On the other hand, the abundance of seven species was significantly different among habitats. Analysis of the abundance matrix shown (axis 1- MANOVA; F2,45 = 16,27; P < 0,001 and axis 2- MANOVA; F2,45 = 6,31; P = 0,004) segregated forest species. The three habitats shared 57,14% of the species collected. The considerable decrease in number of specimens from the forest to the pasture may be related to the lost of vegetation coverage in disturbed areas. The species Brachymetra lata, Brachymetra sp. 1, Cylindrostethus palmaris, Tachygerris celocis, Rhagovelia paulana, Rhagovelia whitei and Neogerris lubricus could be considered indicator species based on significant differences in abundance between disturbed and undisturbed areas.