Caldasia 38 (1):197-210. 2016 RESUMEN El dosel arbóreo constituye un complejo hábitat con gran diversidad de insectos. Los estudios sobre insectos del dosel están mayormente concentrados en bosques húmedos tropicales y son escasos en bosques secos subtropicales. El propósito de este trabajo fue caracterizar la entomofauna del dosel de bosques secos subtropicales, analizando su diversidad regional y localmente. Para ello se muestrearon cinco sitios localizados en la región fitogeográfica del Chaco Semiárido Argentino. Las recolecciones de insectos se realizaron durante el período estival y mediante la técnica de vareo de ramas (beating). Se recolectaron 963 insectos pertenecientes a nueve órdenes y 79 familias. La composición taxonómica y la distribución de la abundancia de familias fueron diferentes en los sitios estudiados. Las condiciones ambientales propias y los disturbios antrópicos de los sitios influyeron en la determinación de los agrupamientos taxonómicos y en la distribución de la abundancia de los insectos. Los resultados que se presentan en este trabajo constituyen los primeros datos sobre la diversidad de insectos del dosel en bosques secos subtropicales, y aportan conocimientos iniciales para futuros estudios sobre interacciones ecológicas y, en general, sobre la diversidad del dosel de estos bosques.Palabras clave. Ensambles de insectos, abundancia, diversidad, Chaco Semiárido, Argentina. ABSTRACTThe canopy is a complex habitat with a great diversity of insects. Most studies on canopy insects refer to tropical rain forests, and seldom to subtropical dry forests. The purpose of this study is to characterize the insect fauna in the canopy of subtropical dry forests, analyzing their diversity both regional and local. Samples were taken in five sites located in the phytogeographical district known as Semiarid Chaco, in Argentina. A total of 963 insects, belonging to 9 orders and 79 families, were collected in the summer by using the "branch-beating" technique. Differences in family abundance distribution and in taxonomic composition were among between sites, resulting in low similarity values. Environmental conditions and human disturbance in the sites might have influenced the taxonomic composition and the distribution of insect abundance. This paper provides the first data on the diversity of canopy insects in subtropical
Cite as: Leiva, M. et al. Assessing disruption of longitudinal connectivity on macroinvertebrate assemblages in a semiarid lowland river. Acta Limnologica Brasiliensia, 2017, vol. 29, e19. Abstract: Aim: Our aim in this study was evaluate the effects of flow regulation for irrigation on the macroinvertebrate assemblages in a semiarid river. Methods: We sampled two reaches in Dulce River; one placed upstream a weir that diverts flow into a network of irrigation channels and the other downstream that weir, in the assessment of the fluvial discontinuity. We assess the differences among reaches and sites, environmental variables, invertebrate density, richness and Shannon-Wiener index applying non-parametric analyses of variance Kruskal Wallis. The similarity percentage analysis (SIMPER) was used to identify which species contributed to the dissimilarities on macroinvertebrate assemblage structure. Canonical Correspondence Analysis (CCA) was performed with the total set of samples to explore macroinvertebrate distribution in reaches and associations of the assemblages with habitat variables. Results: The density, richness and Shannon index values did not show differences between the reaches located upstream and downstream. Beta diversity (Whittaker) was 0.72 among upstream sites, 0.56 among downstream sites and higher species turnover (0.73) was obtained between both reaches. The Canonical Correspondence Analysis explained 46.71% of the variance differentiating upstream sites explained by higher values of organic matter of bottom sediments and discharge, high density of Nais communis, Bothrioneurum americanum, Pelomus, Stephensoniana trivandrana, Pristina menoni, P. jenkinae, P.longidentata, P. americana, Dero obtusa, Endotribelos, Heleobia and Turbellaria. The downstream sites were associated to coarser substratum and higher density of Lopescladius, Polypedilum, Cricotopus, Thienamaniella, Cryptochironomus, Baetidae, Nematoda and Corbicula fluminea. Conclusions: The low-flow disturbance had effects on the composition of the benthic invertebrate assemblages, but attributes (such as density and richness) showed a lower variability probably because of taxa replacement.
Biological monitoring requires a comprehensive baseline of assemblage distribution patterns and their environmental drivers. In this study we evaluated benthic macroinvertebrates in a regulated river, located in a semi-arid region, which has a seasonal flood pulse and is affected by several anthropogenic pressures. Taxonomic and trophic structures of benthic macroinvertebrate assemblages were analysed in terms of their longitudinal distribution, hydrological regime and environmental factors, including the effects of hydromorphology, riparian land use and water abstraction. Most taxa were generalists and classified in the collector–gatherer functional feeding group. A large taxonomic replacement was associated with hydromorphological characteristics. Local environmental variables were critical for macroinvertebrate assemblages. There was significant temporal variability regarding seasonal flood pulse. Water abstraction for irrigation had a strong effect on assemblage structure. We suggest some challenges and issues for successful implementation of biomonitoring tools in the Dulce River, related primarily to high spatiotemporal variability.
El objetivo de este estudio fue evaluar el efecto del hábitat en la aplicación de índices bióticos (BI) basados en macroinvertebrados bentónicos. Se muestrearon dos hábitats, (macrófitas y sedimentos), en dos sitios del río Dulce (Cuenca Salí-Dulce, Argentina): S1 (27° 31’ 5.82” S, 64° 52’ 41.37” O) y S2 (27° 28’ 36.21” S, 64°49’ 30.30” O). El muestreo se realizó con caudal bajo, octubre/2015. Se midió pH, conductividad eléctrica (CE µS/cm), temperatura (T °C), sólidos suspendidos totales (SST mg/L), oxígeno disuelto (OD mg/L) y demanda biológica de oxígeno (DBO5 mg/L). Los macroinvertebrados se filtraron con red de nylon de 250 µm y se identificaron al nivel taxonómico requerido para la aplicación de los IB. Se analizaron riqueza taxonómica y diversidad. Se aplicaron tres IB: el IBMWP, el BMWP’ adaptado al río Salí y el IMRP desarrollado para la ecoregión Pampa de Argentina. También se aplicó el ASPT asociado con los BMWP’. Los parámetros físicos y químicos mostraron buena calidad del agua, con un pH promedio de 8,57; CE 773 µS/cm; T 19,5°C; SST 9,27 mg/L; OD 7,49 mg/L y DBO5 3,29 mg/L. Los taxones registrados fueron 34 y la diversidad fue mayor en las macrófitas que en los sedimentos. Los IB mostraron resultados diferentes según el hábitat donde se aplicaron. Las macrófitas contribuyeron con el doble de taxones a los IB, en comparación con los sedimentos. Los valores de ASPT correspondieron a calidad del agua impactada. El IMRP fue el más inclusivo en cantidad de taxones para el cálculo. La conclusión es que el tipo de hábitats influye en la aplicación de los IB.
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