Riparian vegetation provides the nutrient and energy input that maintains the metabolism and biodiversity in tropical headwater streams. In the present study, it was hypothesised that ~30% of riparian plant species contribute over 70% of coarse particulate organic matter and, because tropical plants are perennial and semi-deciduous, it was expected that leaf fall would occur year round. The aims of the present study were to evaluate the composition and structure of the plant riparian zone and the input and associated benthic stock of organic matter. The riparian vegetation was composed of 99 taxa. The most abundant plant species were Tapirira obtusa, Sclerolobium rugosum, Croton urucurana, Byrsonima sp. and Inga sp. The input and benthic stock showed a seasonal pattern, with higher values recorded at the end of the dry season and at the beginning of tropical storms. The biomass contributed monthly by the vegetation ranged from 28 ± 6 g m–2 to 38 ± 11 g m–2, and the mean monthly benthic standing stock was 138 ± 57 g m–2. The results illustrate the importance of riparian vegetation as an energy source to tropical streams and how individual plant species contribute to organic matter inputs in these ecosystems.

Experimental assessment of temperature increase and presence of predator carcass changing the response of invertebrate shredders. Biota Neotrop. 13(4): http://www.biotaneotropica.org.br/v13n4/en/abstract?article+bn00313042013Abstract: The role of the invertebrate shredders in leaf decomposition process in tropical lotic ecosystems has been explored only recently. In addition to the influence of the quality of litter and the temperature, the risk of predation generally results in changes on the survival and behavior of invertebrate shredders. The aim of this study was to observe the responses of the invertebrate shredders to different species of leaf litters (Experiment 1: Talauma ovata and Inga laurina ; Experiment 2:Talauma ovata , Inga laurina and Richeria grandis ) under gradual temperature rise (24 °C, 26 °C, 28 °C, 30 °C, 32 °C), in the presence (Experiment 2) and absence (Experiment1) of fish (Astyanax sp.) carcasses, as well as to observe the possible consequences of the leaf mass loss (LML). The results from the first experiment suggest that the quality of the litter was capable of changing the feeding preference of the invertebrate shredders, regardless of temperature. In the second experiment, the leaf mass loss was faster in litter with higher quality (Talauma ovate and Richeria grandis ); in addition, we observed that the exploration of these resources resulted in the case-building in the presence of fish carcass. The negative correlation of leaf mass loss of Inga laurina in relation to temperature in the presence of fish carcass probably occurred due to an accelerated metabolic, respiratory and cardiac rates. Apparently, this process may have led to an increased shredding activity on the litters of better quality in relation to the Inga laurina. This fact may be related to less energy consumption, so as to meet their energy demands more efficiently. Keywords: feeding activity, global warming, decomposition. NAVARRO, F.K.S.P., REZENDE, R.S. & GONÇALVES, J.F.Jr. Avaliação experimental de elevação da temperatura e a presença de carcaça do predador alterando a resposta de invertebrados fragmentadores. Biota Neotrop. 13(4): http://www.biotaneotropica.org.br/v13n4/pt/abstract?article+bn00313042013Resumo: O papel dos invertebrados fragmentadores no processo de decomposição foliar em ecossistemas lóticos tropicais vem sendo recentemente explorado. Além da influência da qualidade do detrito e da temperatura, o risco de predação geralmente implica alterações sobre a sobrevivência e comportamento de invertebrados fragmentadores. O objetivo deste estudo foi verificar as respostas dos invertebrados fragmentadores a diferentes espécies de detritos foliares (Experimento 1: Talauma ovata e Inga laurina; Experimento 2: Talauma ovata, Inga laurina e Richeria grandis) sob elevações graduais de temperatura (24 °C, 26 °C, 28 °C, 30 °C, 32 °C), na presença (Experimento 2) e ausência (Experimento1) de carcaças de peixes (Astyanax sp.), assim como verificar as possíveis consequências sobre a perda de massa foliar (PMF). Os...

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The allochthonous detritus that accumulates in the substrate of streams is used by aquatic invertebrate shredders for shelter and food. Shredders are considered rare in tropical systems, and little information is available about the role of density effects and predation risk (associated with the perception of predators by prey) in relationship to the resources used by these organisms. The aim of this study was to examine experimentally the effects of increased predation risk and of the density of Phylloicus sp. (i.e. of two types of biological relationships) on the processing of the leaf litter of Nectandra megapotamica (Spreng.) Mez. Phylloicus sp. can use leaf litter for case building and as a food resource. The density effect was measured using four treatments that differed only in the number of individuals (one, two, three or four). A second experiment with five treatments was performed to test the risk of non-lethal predation on detritus consumption (shelter and food) by Phylloicus sp. (T1: Caddisfly; T2: Mayfly; T3: Astyanax sp./fish; T4: Damselflies; T5: Stonefly). A single Phylloicus and one other organism (a potential predator blocked with 0.5 mm fine mesh) were placed in each tank (0.002 m 3 volume). We observed a negative effect of density on per capita litter consumption (experiment 1). The low density of Phylloicus may be a natural factor that decreases intraspecific competition. In the presence of fish, Phylloicus showed the lowest amount of litter processing observed in the experiment, indicating top-down control (experiment 2). In treatments that involved the presence of invertebrates (non-predatory and predatory), Phylloicus showed the highest amount and an intermediate amount of leaf litter processing, respectively (experiment 2). This observation also suggests that the predation effect is more probable for specific predatorprey pairs. Population density and predation risk in Phylloicus may be important factors controlling leaf litter processing.

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Aim Shredders are generally not abundant in tropical streams, and there is considerable evidence suggesting that the food supply drives this pattern in headwaters. The aim of this study was to assess the effect of variation in the availability of food resources, over one year, on the density of Phylloicus sp. (Trichoptera: Calamoceratidae), which is one of the main shredders in Neotropical headwaters. Methods We measured the relative importance of organic matter in terms of vertical input (VI) and benthic standing stock (BS) on Phylloicus sp. density from October 2012 to September 2013 in a preserved third order stream in the Cerrado savannah biome, Federal District, Brazil. Results Leaves were abundant (monthly biomass of 24.2 g.m–2 ±23.1 SD in VI and 46.1 g.m–2 ±76.7 SD in BS), increasing at the end of dry season (August to October) and comprised the most abundant fraction in VI and BS (~ 70%). Phylloicus sp. had a low density throughout the year (2.4 ind.m–2 ±4.9 SD) and its peak (13.7 ind.m–2 ±17.1 SD in October) was associated with greater leaf biomass in VI and high electrical conductivity in the stream. The well-defined peak of Phylloicus sp. density in October suggests interplay between the increase in Phylloicus density and the leaf litter that enters the stream at the end of the dry season. Electrical conductivity was also higher in October, reflecting an increase in nutrient concentrations in the water during this period. Conclusions The availability of leaf litter may be a determinant factor for the seasonal variation in Phylloicus sp. density in tropical streams, suggesting a bottom-up effect. Changes in the supply of allochthonous resources to the stream can lead to modification in populations of shredders, such as Phylloicus sp., and anthropogenic influences on the riparian vegetation can affect ecological processes of great importance to streams.

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