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Protecting riparian vegetation around streams is vital in reducing the detrimental effects of environmental change on freshwater ecosystems and in maintaining aquatic biodiversity. Thus, identifying ecological thresholds is useful for defining regulatory limits and for guiding the management of riparian zones towards the conservation of freshwater biota. Using nationwide data on fish and invertebrates occurring in small Brazilian streams, we estimated thresholds of native vegetation loss in which there are abrupt changes in the occurrence and abundance of freshwater bioindicators and tested whether there are congruent responses among different biomes, biological groups and riparian buffer sizes. Mean thresholds of native vegetation cover loss varied widely among biomes, buffer sizes and biological groups: ranging from 0.5% to 77.4% for fish, from 2.9% to 37.0% for aquatic invertebrates and from 3.8% to 43.2% for a subset of aquatic invertebrates. Confidence intervals for thresholds were wide, but the minimum values of these intervals were lower for the smaller riparian buffers (50 and 100 m) than larger ones (200 and 500 m), indicating that land use should be kept away from the streams. Also, thresholds occurred at a lower percentage of riparian vegetation loss in the smaller buffers, and were critically lower for invertebrates: reducing only 6.5% of native vegetation cover within a 50‐m riparian buffer is enough to cross thresholds for invertebrates. Synthesis and applications. The high variability in biodiversity responses to loss of native riparian vegetation suggests caution in the use of a single riparian width for conservation actions or policy definitions nationwide. The most sensitive bioindicators can be used as early warning signals of abrupt changes in freshwater biodiversity. In practice, maintaining at least 50‐m wide riparian reserves on each side of streams would be more effective to protect freshwater biodiversity in Brazil. However, incentives and conservation strategies to protect even wider riparian reserves (~100 m) and also taking into consideration the regional context will promote a greater benefit. This information should be used to set conservation goals and to create complementary mechanisms and policies to protect wider riparian reserves than those currently required by the federal law.

Leaf breakdown in streams is affected by several factors, such as leaf characteristics, water chemistry, microbial activity, and abundance of shredders. In turn, shredders may be resourcecontrolled. We hypothesized that the size of litter patches affects leaf breakdown, because large patches should be stable over time and therefore harbor high densities of shredders. We selected litter patches (area 0.25-10 m 2 ) in 10 pools of three first-order streams (Manaus, Brazil). We installed 10 leaf packs of Mabea speciosa (Euphorbiaceae) in each patch, and sampled one after 1 day and three after 5, 19, and 28 days. The leaf packs were quickly colonized by the shredding caddisflies Triplectides and Phylloicus. The leaf breakdown rate (mean k = 0.026 ± 0.0015 SE) was high and similar to values reported for other tropical and temperate streams, although much higher than values reported for the adjacent Cerrado biome. Assemblage composition varied over time, but was not related to the size of litter patches. Contrary to our hypothesis, litter patch area did not affect breakdown rates (r 2 = 0.012, P = 0.766) or abundance of shredders after 5, 19, and 28 days (r 2 \ 0.243, P [ 0.147). We found, however, a positive relationship between the abundance of tropical shredders and leaf breakdown after 19 days (r 2 = 0.572, P = 0.011), suggesting that shredders play an important role in leaf breakdown in these headwater streams. Our study indicates that leaf breakdown rates in tropical streams are variable and can be as high as those of temperate streams.

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1. To understand how the semiaquatic bug communities are shaped, it was first verified whether there was a pattern of co‐occurrence between species. It was subsequently tested whether the pattern found was related to environmental variables. Lastly, it was verified whether morphological divergence between species was present in the morphological and functional traits selected.2. A pattern of species co‐occurrence was found in the studied assemblage, related to both environmental variables and interspecific biological interactions. Pairs of species with negative, positive, and random co‐occurrence were found. Traits related to predation competition, sexual competition, and interaction with the environment showed significant morphological divergence.3. Therefore, more than one process defines species co‐occurrence patterns in semiaquatic bug communities. It is suggested that environmental influence is related to species microhabitat preference. On the other hand, the morphological divergence found is related to competition and sharing of food resources.

ABSTRACT. Mosquitoes (Diptera, Culicidae) inhabiting foliar tanks of Guzmania brasiliensis Ule (Bromeliaceae) in central Amazonia, Brazil. Mosquitoes in the family Culicidae develop their immature forms in different environments depending on various circumstances. This study represents the first contribution to the ecological knowledge of culicids living in the bromeliad G. brasiliensis. The objectives of the study were to compare the Culicidae fauna of bromeliads in two seasonal periods, analyzing their abundance, richness and the influence of pH, conductivity and water volume, on the populations. Sampling was done at Reserva Adolpho Ducke, Manaus, Amazonas, Brazil between 2003 and 2005. Six samplings were done in the rainy season and six in the dry season. On each sampling day, six terrestrial and six epiphytic bromeliads, totaling 144 sampling units, were retrieved. A total of 444 immature mosquitoes were collected, distributed in the following species:The relationship between abundance of Culicidae and sampling period was not significant, although abundance was higher in the dry period. There were significant correlations between water volume and the abundance (p = 0.003) and richness (p = 0.001) of culicids. The pH was positively related to the occurrence of the species Wy. autocratica (p= 0.010) and Wy. splendida (p= 0.006), demonstrating the influence of this factor in the structuring of bromeliadinhabiting communities.KEYWORDS. Amazon; Aquatic insects; Culex (Microculex); Phytotelmata; Wyeomyia.RESUMO. Mosquitos (Diptera, Culicidae) habitando tanques foliares de Guzmania brasiliensis Ule (Bromeliaceae) na Amazônia Central, Brasil. Mosquitos da família Culicidae desenvolvem suas formas imaturas em vários ambientes na dependência de circunstâncias diversas. Este trabalho representa a primeira contribuição ao conhecimento ecológico de culicídeos em G. brasiliensis e tem como objetivo inventariar os imaturos em bromélias em dois períodos sazonais, analisando a abundância, riqueza e a influência das variáveis abióticas pH, condutividade e volume de água sobre as populações de Culicidae. A relação entre abundância de Culicidae e períodos não foi significativa, entretanto, o período seco apresentou maior representatividade de imaturos. Houve significância na relação do volume de água e abundância (p= 0,003) e riqueza (p= 0,001) de culicídeos. O pH foi o único parâmetro relacionado positivamente com a ocorrência das espécies Wy. autocratica (p= 0,010) e Wy. splendida (p= 0,006) ressaltando a influência deste fator na estruturação das comunidades bromelícolas.