RESUMEN Este trabajo presenta una caracterización de los grupos tróficos de las comunidades de invertebrados que habitan en tres quebradas y caños de las llanuras aluviales de la Orinoquía colombiana. Los muestreos de las comunidades se realizaron en tres arroyos durante los meses de julio de 2016, octubre de 2016 y enero de 2017). En tramos de 50 m se midieron variables fisicoquímicas [temperatura (°C), oxígeno disuelto (mg l-1 O2), pH, conductividad (µS cm-1), amonio (µg l-1NH4+) y fosfatos (µg l-1 PO4 - )] e hidrológicas (caudal m3 s-1 ); adicionalmente, se tomaron cinco muestras de macroinvertebrados en sustratos rocosos. La diversidad se determinó usando el índice de Shannon, la comparación entre puntos de muestreo se utilizó el índice de Morisita-Horn y para el análisis multivariado de la temporalidad, las variables fisicoquímicas y los organismos se llevó a cabo un Análisis de Redundancias (RDA). Los contenidos estomacales de los individuos recolectados se identificaron para los géneros más representativos. Los Colectores-Recolectores fueron el grupo más abundante y su alto número se mantuvo durante todos los muestreos; sin embargo, su abundancia y riqueza alcanzaron su pico máximo durante la estación seca. El RDA indicó que el caudal y la temperatura permiten explicar, parcialmente, la variación temporal en la ocurrencia y abundancia de los diferentes grupos tróficos. En general, los hallazgos demuestran que los organismos adaptan su dieta a la oferta disponible en su medio, por lo que es importante realizar su clasificación trófica en los diferentes ecosistemas.

ABSTRACT A characterization of the trophic groups of the invertebrate communities in three streams and channels of the alluvial plains of the Colombian Orinoquia is presented. The sampling of the communities was carried out in three streams during July (2016), October (2016), and January (2017). Physicochemical [temperature (°C), dissolved oxygen (mg l-1 O2), pH, conductivity (µS cm-1), ammonia (µg l-1 NH4+ ), and phosphates (µg l-1PO4 -)] and hydrological (flow m3 s-1) variables were measured. In 50 m reaches of each sampling site, five samples of macroinvertebrates were taken in rocky substrates. Organisms were identified, and diversity was determined using the Shannon index. The comparison between sampling points was made using the Morisita-Horn index and the multivariate analysis between temporality, physicochemical variables, and organisms was performed with the Redundancy Analysis (RDA). The stomach contents of the collected individuals were identified for the more representative genera, and each genus was assigned to a specific trophic group according to their intestinal contents and mouthparts. The Collectors-Gatherers were the most abundant group in the three streams, and their high number was maintained during all the samplings. However, their abundance and richness reached their maximum peak during the dry season. The RDA indicated that water flow and temperature partially explain the temporal variation in the occurrence and abundance of the different trophic groups. In general, the findings show that organisms adapt their diet to the offer available in their environment, and therefore it is important to classify them trophically in the different ecosystems.

El objetivo de este estudio fue determinar la estructura comunitaria de macroinvertebrados dulceacuícolas y caracterizar los grupos funcionales tróficos en la cuenca del río Lluta ubicado en el desierto de Atacama. Para esto se muestreó con una red Surber en 12 estaciones, abarcando desde la cabecera del río hasta su desembocadura en la costa marítima durante noviembre de 2011. En este estudio se registraron 66 taxa de macroinvertebrados, correspondiendo en su mayoría a larvas de insectos (46). Los grupos con mayor riqueza fueron Diptera (20 taxa), Coleoptera y Trichoptera (ambos con 7 taxa). Respecto de la abundancia, Chironomidae fue la familia más abundante del área de estudio. El grupo de los colectores-recolectores fue el más representativo en 10 de las 12 estaciones, mientras que el grupo de los ramoneadores dominaron en las dos estaciones más cercanas a la desembocadura. Nuestros resultados son los primeros en describir la fauna de macroinvertebrados dulceacuáticos en la cuenca más extrema del norte de Chile, conteniendo una riqueza faunística mucho mayor que otras cuencas desérticas. Además la gran representatividad de los colectores-recolectores que se alimentan de fragmentos orgánicos menores a 1 mm depositados en el fondo, demuestran la importancia de este recurso alimentario en ríos del desierto de Atacama.

The aim of this study was to determine the community structure of freshwater macroinvertebrates and characterize trophic functional groups in the Lluta river basin located in the Atacama Desert. To this was sampled with Surber sampling in 12 stations, in extension from the source to its mouth on the coast during November 2011. In this study 66 taxa of macroinvertebrates were recorded, corresponding mostly insect larvae (46). The groups with the greatest wealth were Diptera (20 taxa), Coleoptera and Trichoptera (both with 7 taxa). On abundance, Chironomidae was the most abundant family of the study area. The group of collectors-gatherers was the most representative in 10 of the 12 stations, while the group of browsers dominated the two closest stations to the mouth. Our results are the first to describe the fauna of macroinvertebrates dulceacuáticos in extreme northern Chile basin, containing a much higher than other rich fauna desert basins. Besides the great representative of the collectors-gatherers that feed on organic fragments under 1 mm deposited on the bottom, showing the importance of this food source in the Atacama desert rivers.

Aquatic macroinvertebrates are involved in numerous processes within aquatic ecosystems. They often have important effects on ecosystem processes such as primary production (via grazing), detritus breakdown, and nutrient mineralization and downstream spiraling. The functional feeding groups (FFG) classification was developed as a tool to facilitate the incorporation of macroinvertebrates in studies of aquatic ecosystems. This classification has the advantage of combining morphological characteristics (e.g., mouth part specialization) and behavioral mechanisms (e.g., way of feeding) used by macroinvertebrates when consuming resources. Although recent efforts have greatly advanced our ability to identify aquatic macroinvertebrates, there is limited information on FFG assignment. Furthermore, there has been some variation in the use of the FFG classification, in part due to an emphasis on using gut content analysis to assign FFG, which is more appropriate for assigning trophic guilds. Thus, the main goals of this study are to (1) provide an overview of the value of using the FFG classification, (2) make an initial attempt to summarize available information on FFG for aquatic insects in Latin America, and (3) provide general guidelines on how to assign organisms to their FFGs. FFGs are intended to reflect the potential effects of organisms in their ecosystems and the way they consume resources. Groups include scrapers that consume resources that grow attached to the substrate by removing them with their mouth parts; shredders that cut or chew pieces of living or dead plant material, including all plant parts like leaves and wood; collectors-gatherers that use modified mouth parts to sieve or collect small particles (<1mm) accumulated on the stream bottom; filterers that have special adaptations to remove particles directly from the water column; and predators that consume other organisms using different strategies to capture them. In addition, we provide details on piercers that feed on vascular plants by cutting or piercing the tissue using sharp or chewing mouth parts and consume plant liquids. We also provide a list of families of aquatic insects in Latin America, with an initial assignment to FFGs. We recommended caution when assigning FFGs based on gut contents, as it can provide misleading information. Overall, FFG is a very useful tool to understand the role of aquatic macroinvertebrates in stream ecosystems and comparisons among studies will benefit from consistency in their use. Rev. Biol. Trop. 62 (Suppl. 2): 155-167. Epub 2014 April 01.