Variación espacio-temporal de macroinvertebrados acuáticos en la Lindosa, Guayana colombiana

Introducción: Describir los patrones de biodiversidad y los mecanismos que los subyacen es indispensable para afrontar las desenfrenadas presiones sobre los ecosistemas de agua dulce en el trópico. Esto es particularmente relevante en regiones escasamente estudiadas como el escudo guayanés colombiano Objetivo: Describir la estructura taxonómica y funcional de las comunidades de macroinvertebrados, y evaluar su variación a lo largo de escalas espaciales y temporales Métodos: Las comunidades de macroinvertebrados de cuatro ríos fueron muestreadas durante la época seca del 2017 y 2018. Adicionalmente, se evaluaron los patrones de diversidad dentro y entre los ríos y entre diferentes meses de muestreo en uno de los cursos hídricos. Los patrones de diversidad fueron evaluados mediante la comparación de los patrones entre y dentro de los ríos de la diversidad alfa (diferencias en la riqueza y abundancia de taxones entre comunidades) y de la diversidad beta (diferencias en la composición de taxones entre comunidades). La diversidad alfa fue estimada usando los números de Hill, mientras que la diversidad beta se estimó usando los índices de Sørensen y Morisita-Horn y comparada usando un análisis de similaridad (ANOSIM). Resultados: La composición de taxones fue distinta dentro (escala de mesohábitat) y entre los ríos (escala regional). Sin embargo, la composición de FFG cambió entre, pero no dentro de los ríos. La comparación de los números de Hill y de la composición de taxones sugiere que el tipo de mesohábitat es un factor determinante de la diversidad taxonómica pero no de la diversidad de FFG en distintas escalas. En la escala temporal, la diversidad alfa fue baja para los meses con altas precipitaciones (febrero-abril) y alta para la temporada seca (enero). La diversidad beta temporal fue alta para los periodos muestreados y los procesos de anidamiento fueron el componente más notable de la diversidad beta a lo largo del año. Conclusión: Los ríos de la Serranía de la Lindosa albergan una alta diversidad de macroinvertebrados acuáticos. La estacionalidad y las diferencias en la heterogeneidad del hábitat dentro de los ríos parecen determinar los patrones de diversidad observados a diferentes escalas temporales y espaciales. Profundizar en su estudio es necesario para entender el funcionamiento de estos ecosistemas y mejorar la habilidad para generar estrategias de manejo y conservación.

Introduction: Describing biodiversity patterns and the underlying drivers is relevant for tackling the rampant pressures on tropical freshwaters. This is particularly relevant in scarcely studied regions, such as in the Colombian Guiana shield. Objective: To describe the taxonomic and functional structure of macroinvertebrate communities and assess their variability across spatial and temporal scales. Methods: We sampled the invertebrate communities in four streams during the dry seasons of 2017 and 2018. Additionally, we assessed diversity patterns within and among streams and between different sampling months in one stream. To assess diversity patterns, we compared alpha (differences in taxon richness and abundance within communities) and beta (differences in taxon composition among communities) diversity patterns among and within rivers. Alpha diversity was estimated using the numbers of Hill, while beta diversity was estimated using the Sørensen and Morisita-Horn indices and compared using a similarities analysis (ANOSIM). Results: The taxon composition of the communities was different within (mesohabitat scale) and among streams (regional scale). However, the composition of FFGs changed among but not within streams. The comparison of the numbers of Hill and the taxon composition suggested that the mesohabitat type is a determining factor of the taxonomic but not FFG diversity across scales. At the temporal scale, alpha diversity was low for months with high precipitation (February-April) and high for the dry season (January). The temporal beta diversity was high among sampling periods, being nestedness processes driving beta diversity among years and turnover processes driving beta diversity within years. Conclusion: Streams from Serranía de la Lindosa host a high diversity of freshwater macroinvertebrates. Seasonality and differences in the in-stream habitat heterogeneity seem to determine the diversity patterns observed at different temporal and spatial scales. A deeper study is needed to understand the functioning of these ecosystems and improve the ability to generate management and conservation strategies.

Ecological studies of mayflies (Insecta, Ephemeroptera): Can sampling effort be reduced without losing essential taxonomic and ecological information? / Estudos ecológicos com Ephemeroptera (Insecta): O esforço amostral pode ser reduzido sem perder informações ecológicas e taxonômicas?

ABSTRACT The present study evaluated the potential for the reduction of sampling effort in studies of ephemeropteran nymphs in Brazilian Amazon streams, Pará State, Brazil, without the loss of ecological information (species composition, abundance, and richness), and the congruence of different levels of taxonomic resolution (morphospecies, genus, family and functional group). Test groups of 15, 10 and five subsamples were selected from the 20 subsamples collected per stream (40 streams sampled), and were compared in terms of their species richness and abundance (ANOVA), and composition (Procrustes). Taxonomic resolution was also analyzed in Procrustes. Species abundance (F(3, 156) = 25.426; p < 0.001) and richness (F(3, 156) = 13.866, p < 0.001) varied significantly among sample groups, while the results of the 15-S group were statistically similar, in both cases, to those of the 20-S group. A similar pattern was found for species composition. The genus-level taxonomic resolution produced results 99% similar to those found for the species-level data. The results indicate that the reduction in sampling effort from 20 to 15 subsamples per site and a genus-level taxonomic resolution would not affect the reliability of analyses significantly. A reduction of five samples per site would result in a decrease of effort in the field and the amount of material to be processed, reducing laboratory time. In addition to a reduction in the time and resources needed to identify specimens, the adoption of a genus-level taxonomic resolution could help minimize errors of under- or over-estimation in the processing of the results.

RESUMO O presente estudo avaliou o potencial para redução do esforço amostral em estudos com ninfas de Ephemeroptera em igarapés amazônicos, no estado do Pará, Brasil, sem perder informações ecológicas (composição de espécies, abundância e riqueza), além de verificar se existe congruência entre diferentes níveis de resolução taxonômica (morfoespécie, gênero, família e grupo funcional). Grupos reduzidos de 15, 10 e cinco subamostras de um controle de 20 amostras de cada um dos 40 igarapés amostrados, foram comparados quanto a riqueza de táxons e abundância (ANOVA) e composição (Procrustes). A resolução taxonômica também foi avaliada através do Procrustes. A abundância (F(3, 156) = 25,426; p < 0,001) e riqueza (F(3, 156) = 13,866, p < 0,001) variaram significativamente entre os grupos de amostras, porém, os resultados tanto de riqueza quanto de abundância dos grupos 15-S foram estatisticamente similares aos de 20-S. O mesmo padrão foi encontrado para riqueza de espécies. A resolução taxonômica a nível de gênero obteve 99% de congruência com a de morfoespécie. Esses resultados indicam que a diminuição de 20 subamostras para 15, e a redução da identificação de morfoespécie para gênero não afetaria a significância das análises. A redução de cinco amostras por local de coleta poderia resultar em uma diminuição do esforço em campo e do material para ser processado em laboratório, reduzindo o tempo de triagem e identificação. Ainda, para reduzir tempo e recursos financeiros gastos para coleta e identificação dos organismos, a identificação apenas a nível genérico poderia minimizar erros de sub ou super estimativa no processamento dos resultados.

Trophic analysis of three species of Marilia (Trichoptera: Odontoceridae) from the neotropics / Análisis trófico de tres especies de Marilia (Tri-choptera: Odontoceridae) del neotrópico

The trophic ecology of the aquatic insect fauna has been widely studied for the Northern temperate zone. However, the taxa originally classified within a given particular trophic group in temperate ecosystems, do not necessarily exhibit the same dietary profile beyond its geographic limits. Since, the trophic ecology of caddisfly larvae is largely incomplete in the Neotropical Region, the present work aims to describe feeding habits inferred from quantitative analysis of data taxonomically resolved at the species level. For this, the feeding habits of three Trichoptera species Marilia cinerea, M. elongata and M. flexuosa were recorded in the Yungas forests of Argentina and Bolivia. A total of 15 larvae of each species were sampled from 13 different streams were selected for gut content analysis. The ingested material was extracted from the foregut and midgut by using ventral dissection of thorax. For each species, mandibles were dissected, mounted in glycerin and illustrated in order to highlight morphological differences between these mouth pieces purportedly associated to the dietary behavior of individuals, and their habitats. The niche overlap was estimated through Schoener’s method. The diet analysis revealed that M. cinerea, M. elongata and M. flexuosa feed on the same food items, but through different patterns of preferences. Larvae of M. cinerea were collected on both emerging surfaces of rocks on which a thin layer of running water flows and streams sliding areas with stony bottoms attached to the rock surfaces. They displayed a gut content consisting predominantly of invertebrate vestiges and have strong mouthparts provided of large molar areas; this allowed us to allocate the species within the functional group of predators. M. elongata feeds mainly on fine particulate material, its mouthparts are scoop-shaped and occurs in areas of low flow; this set of features is linked to a collector-gatherer strategy. Finally, larvae of M. flexuosa have been primarily assigned to the functional group of shredders and secondarily to the collector-gatherer class. They inhabit sandy bottoms of mountain streams, have strong scoop-shaped mouthparts and show a diet dominated by leaf litter and fine particulate material. We concluded that the functional group assignment to the genus level for Marilia is not recommended, and further studies at species level are necessary. Rev. Biol. Trop.62 (2): 543-550. Epub 2014 June 01.

La ecología trófica de insectos acuáticos ha sido desarrollada en zonas templadas. Sin embargo, la asignación de un taxón a un grupo trófico no representa necesariamente el mismo en otras regiones. En la Región Neotropical, el conocimiento sobre la ecología trófica de larvas de tricópteros es incompleta y la literatura sobre este tema rara vez se ocupa del análisis de los hábitos alimentarios de larvas con datos cuantitativos a nivel de especie. Este trabajo aporta al conocimiento de las características tróficas de la trichopterofauna del Neotrópico. Se describen los hábitos alimentarios de tres especies de Trichoptera registrados en arroyos de Yungas de Argentina y Bolivia: Marilia cinerea, M. elongata y M. flexuosa. Se seleccionaron 15 larvas de cada especie en 13 arroyos de Yungas surandinas para analizar las piezas bucales y el contenido estomacal. El solapamiento de nicho trófico se estimó mediante el índice de Schoener. El análisis de la dieta reveló que las especies difieren en la preferencia de los ítems registrados, hábitat y forma de sus mandíbulas. Las larvas de M. cinerea habitan en superficies de rocas emergentes. Poseen mandíbulas fuertes con grandes zonas molares y consumen principalmente invertebrados. Esta evidencia permite asignarle el grupo funcional depredador. M. elongata consume material fino, sus mandíbulas tienen forma de cuchara y su ubicación en zonas de bajo flujo permite asignarle una estrategia colectora-recolectora. Las larvas de M. flexuosa habitan en fondos arenosos de arroyos de montaña, tienen fuertes piezas bucales en forma de cuchara y una dieta dominada por hojarasca y material fino. Pertenecen al grupo funcional triturador, secundariamente colector-recolector. Sugerimos que la asignación de grupo funcional a nivel de género no es recomendable para Marilia. Se recomiendan mayores estudios a nivel de especie.