ABSTRACT Stream insects use in different ways the stream habitats which affect patterns of species occurrence on stream. The nestedness is one of these patterns being an ecological mechanism that generates beta diversity. In this study, we verify the effects of temporal environmental variations on nestedness patterns of Chironomidae assemblages on subtropical streams. We collected chironomid larvae during winter and summer during three years (2010, 2011 and 2012) in Brazilian Subtropical low-order streams (Erechim, state of Rio Grande do Sul, Brazil). We measured environmental variables in each stream. To assess if assemblages will show nested patterns intra- and interannual we used a NODF metric. We observed nestedness only in one year, this pattern was due to variation of limnological factors, which are directly associated with climatic conditions (precipitation and water temperature) and agricultural management (e.g. dissolved oxygen and nutrients). Climatological events affect Chironomidae community through the time. The variations on precipitation values could be one of the mainly factors that influence nestedness for this community. Finally, studies on nesting on time scales should consider inter-annual comparisons, as climatic variations are more evident.

The structure and composition of stream benthic communities are strongly influenced by spatial and temporal factors. This study evaluated the intra and inter-annual variations in Chironomidae communities in subtropical streams. The organisms were sampled from 10 small-order streams during the summer and winter of 2010-2012. The number of chironomid specimens sampled was 7,568, distributed in 49 genera. Chironomid abundance and richness varied intra and inter-annually and community composition varied intra-annually (2010 and 2011). Water temperature, total organic carbon, nitrogen, and rainfall were correlated with chironomid community composition. The intra-annual variation of the community was dependent on climatic variations (temperature and rainfall) and changes caused by intensive agricultural use. We conclude that the temporal variation observed in the Chironomidae community correlates with climatic variations (rainfall) and changes in the total organic carbon and total nitrogen, caused by intensive agricultural land use.

Trabalhos com ecologia de riachos tem buscado compreender os padrões de distribuição das comunidades aquáticas procurando responder de que forma os fatores locais e regionais, infuenciam na ocorrência e persistência de determinadas espécies nesses ecossistemas. Este estudo investigou a infuência dos usos e ocupação da terra sobre a comunidade de Chironomidae em riachos em duas áreas de drenagem no sul do Brasil. Larvas de Chironomidae foram coletadas em riachos de 1a e 2a ordens. A zona ripária dos riachos (30 m em ambas as margens) teve sua paisagem analisada utilizando técnicas de geoprocessamento e diferentes usos e ocupação da terra foram classifcados e quantifcados. Os usos e ocupação da terra foram diferentes entre as duas áreas de drenagem estudadas. Da mesma forma, a composição da comunidade de Chironomidae nos riachos foi diferente entre as duas áreas de drenagem. Dentre os diferentes usos e ocupação da terra quantifcados, a comunidade foi infuenciada principalmente pela agricultura e vegetação arbórea nativa. As variações na paisagem demonstraram que o aumento na área de agricultura e a diminuição da área de vegetação ripária são os principais atributos da paisagem que infuenciam as comunidades de Chironomidae.

Landscape integrity and influence on Chironomidae composition assemblages in small order streams: Studies in stream ecology are aimed at understanding the patterns of distribution of aquatic communities, trying to answer how local and regional factors influence the occurrence and persistence of species in these ecosystems. This study investigated the influence of land use on the Chironomidae community in streams in two drainage areas in southern Brazil. Chironomid larvae were collected in1st and 2nd orders. The riparian zone of streams (30 m on both sides) had its landscape analyzed using GIS techniques, and land uses classified as consistent and non-consistent. The land use influence was different between the two drainage areas. Likewise, the composition of Chironomidae community in streams was different between the two drainage areas. Among the different land uses, the community was influenced mainly by agriculture and arboreous vegetation. We conclude that the aquatic communities respond to environmental changes not only at local scale but also at broader scales, such as landscape features of the surrounding areas.