-The aim of this study was to examine the relationship between the emergence patterns of various groups of aquatic insects and different hydrological discharge periods. We hypothesize that hydrological fluctuations exert a strong influence on insect emergence, even though the orders show different responses to discharge frequency. The emergence of Diptera, Trichoptera and Ephemeroptera was measured in a tropical stream with a mesh emergence net. The sampling took place every 2 days for 14 months. Based on water flow records taken throughout the sampling period nine discharge categories were defined. A significant relationship between macroinvertebrate emergence and discharge was found, and a high percentage of emergences was fundamentally concentrated within two discharge categories namely < 0.352 m . We used a time series consisting of 60 weekly samples to describe how emergence varied in an intra-annual period. Autoregressive integrated moving average (ARIMA) models were applied to analyze the time series of data collected for macroinvertebrate order. Time-series models for Trichoptera and Ephemeroptera showed a lagging relationship between the moving average (MA) of the emergences and environmental and biological factors, which occurred one (MAI) and two (MAII) periods earlier, respectively. For Diptera, a relationship was found between emergence and discharge for the autoregressive (AR) order. The relationship was regulated by the autecology of the organisms and occurred AR two time periods earlier (AR2). This study showed that the response of macroinvertebrates to discharge can be differentiated and can produce relevant changes in biodiversity.
Nutrient excess is a common disturbance that affects biological interactions in river ecosystems. The response of nutrient supply on primary producers and Tricorythodes sp., a common mayfly grazer, was determined in experimental chambers set in a tropical, high Andean stream. Chambers in an experimentally fertilized reach developed higher amount of both benthic and detached chlorophyll than chambers in an upstream control reach. Fertilization produced a slight increase in grazer biomass, and reduced algal biomass compared to grazer-free chambers. These results show that nutrient excess spread bottom-up effects through the food web, and that relevant top-down effects could also be detected. Eutrophication may produce relevant changes in the food web of tropical high-mountain streams.
Existen dificultades para determinar el peso de los macroinvertebrados y conocer así su importancia energética dentro de un ecosistema acuático. Por lo tanto, el objetivo de este estudio fue hallar relaciones matemáticas entre la longitud y la biomasa en dos géneros de invertebrados, representativos en el humedal Jaboque (Engativá) Bogotá D. C., Colombia, que faciliten hallar el peso de los individuos. Para ello, se realizaron cuatro muestreos desde abril de 2009 a enero de 2010. Se obtuvieron ecuaciones para estimar el peso seco a partir de medidas de la longitud total del cuerpo, para los géneros Helobdella y Asellus. Las relaciones halladas entre longitud total y peso seco fueron significativas y explicaron al menos el 69% de la varianza, expresada en los coeficientes de correlación (r2 = 0,69 y 0,85). Estos modelos permitirán calcular la biomasa para determinar el crecimiento y la producción secundaria de estos taxones en posteriores estudios de laboratorio o de campo. También podrían ayudar a conocer la importancia de estos organismos en el flujo de energía en los ecosistemas acuáticos, principalmente en los humedales andinos urbanos, donde son muy abundantes.
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