Chironomidae feeding habits in different habitats from a Neotropical floodplain: exploring patterns in aquatic food webs.

Ecological studies on food webs have considerably increased in recent decades, especially in aquatic communities. Because Chironomidae family are highly specious, occurring in almost all aquatic habitats is considered organisms-key to initiate studies on ecological relationships and trophic webs. We tested the hypothesis that the diversity of the morphospecies diet reflects differences on both the food items available among habitats and the preferences of larval feeding. We analyzed the gut content of the seven most abundant Chironomidae morphospecies of the different habitats from the Upper Paraná River. We categorized the food items found into algae, fungal spores, fragments of plants, algae and animal fragments and sponge spicules. We observed the algae predominance in the gut content of morphospecies from lakes. Considering the different regions from each lake, we registered the highest food abundance in the littoral regions in relation to the central regions. From the variety of feeding habits (number of item kinds), we classified Chironomus strenzkei, Tanytarsus sp.1, Procladius sp.1 as generalist morphospecies. We found a nested pattern between food items and Chironomidae morphospecies, where some items were common to all taxa (e.g., Bacillariophyceae algae, especially), while others were found in specific morphospecies (e.g., animals fragments found in Procladius sp.1). The algae represented the most percentage of gut contents of Chironomidae larvae. This was especially true for the individuals from littoral regions, which is probably due to the major densities of algae associated to macrophytes, which are abundant in these regions. Therefore, the feeding behavior of these morphospecies was generalist and not selective, depending only of the available resources.

Chironomidae feeding habits in different habitats from a Neotropical floodplain: exploring patterns in aquatic food webs / Hábitos alimentares de Chironomidae em diferentes habitats de uma planície de inundação Neotropical: explorando padrões em redes alimentares aquáticas

Abstract Ecological studies on food webs have considerably increased in recent decades, especially in aquatic communities. Because Chironomidae family are highly specious, occurring in almost all aquatic habitats is considered organisms-key to initiate studies on ecological relationships and trophic webs. We tested the hypothesis that the diversity of the morphospecies diet reflects differences on both the food items available among habitats and the preferences of larval feeding. We analyzed the gut content of the seven most abundant Chironomidae morphospecies of the different habitats from the Upper Paraná River. We categorized the food items found into algae, fungal spores, fragments of plants, algae and animal fragments and sponge spicules. We observed the algae predominance in the gut content of morphospecies from lakes. Considering the different regions from each lake, we registered the highest food abundance in the littoral regions in relation to the central regions. From the variety of feeding habits (number of item kinds), we classified Chironomus strenzkei, Tanytarsus sp.1, Procladius sp.1 as generalist morphospecies. We found a nested pattern between food items and Chironomidae morphospecies, where some items were common to all taxa (e.g., Bacillariophyceae algae, especially), while others were found in specific morphospecies (e.g., animals fragments found in Procladius sp.1). The algae represented the most percentage of gut contents of Chironomidae larvae. This was especially true for the individuals from littoral regions, which is probably due to the major densities of algae associated to macrophytes, which are abundant in these regions. Therefore, the feeding behavior of these morphospecies was generalist and not selective, depending only of the available resources.

Resumo Estudos sobre redes alimentares têm aumentado consideravelmente nas últimas décadas em pesquisas de ecologia, principalmente em comunidades aquáticas. Em função Família Chironomidae ser altamente especiosa, ocorrendo em quase todos os hábitats aquáticos, é considerada como organismos-chave para estudos preliminares sobre as relações ecológicas como redes tróficas. Nós testamos a hipótese de que a diversidade de dietas das morfoespécies reflete diferenças tanto na disponibilidade dos itens alimentares entre os hábitats analisados, quanto preferencias alimentares das larvas. Nós analisamos o conteúdo digestivo das sete morfoespécies mais abundantes de diferentes habitats da planície de inundação do alto rio Paraná. Nós categorizamos os itens alimentares encontrados como algas, esporos de fungos, fragmentos vegetais, fragmentos de algas ou de animais e espículas de esponjas. Nós observamos a predominância de algas no conteúdo digestivo das morfoespécies lacustres. Considerando as diferentes regiões de cada lagoa, nós registramos as maiores abundâncias de alimentos nas regiões litorâneas, quando comparadas com as regiões centrais. A partir da variedade de hábitos alimentares (número de tipos de itens), classificamos Chironomus strenzkei, Tanytarsus sp.1 e Procladius sp.1 como morfoespécies generalistas. Nós encontramos um padrão aninhado entre os itens alimentares e as morfoespécies de Chironomidae, onde alguns itens foram comuns a todos os táxons (por exemplo, algas da Classe Bacillariophyceae), enquanto outros foram encontrados em morfoespécies mais especificas (por exemplo, fragmentos de animais encontrados em Procladius sp.1). As algas representaram a maior porcentagem do conteúdo digestivo das larvas de Chironomidae. Este fato foi especialmente verdadeiro para os indivíduos das regiões litorâneas, o qual é devido, provavelmente, pelas maiores densidades de algas associadas à macrófitas, que são abundantes nessas regiões. Portanto, o comportamento alimentar dessas morfoespécies foi generalista e não seletivo, dependendo apenas dos recursos disponíveis.

Chironomidae larvae (Diptera) of Neotropical floodplain: overlap niche in different habitats.

The niche overlap between trophic groups of Chironomidae larvae in different habitats was observed between trophic groups and between different environments in Neotropical floodplain. For the evaluation we used the index of niche overlap (CXY) and analysis of trophic networks, both from the types and amount of food items identified in the larval alimentary canal. In all environments, the larvae fed on mainly organic matter such as plants fragments and algae, but there were many omnivore larvae. Species that have high values of food items occurred in diverse environments as generalists with great overlap niche and those with a low amount of food items with less overlap niche were classified as specialists. The largest number of trophic niche overlap was observed among collector-gatherers in connected floodplain lakes. The lower values of index niche overlap were predators. The similarity in the diet of different taxa in the same niche does not necessarily imply competition between them, but coexistence when the food resource is not scarce in the environment even in partially overlapping niches.

Habitats and trophic relationships of Chironomidae insect larvae from the Sepotuba River basin, Pantanal of Mato Grosso, Brazil.

Benthic habitats are linked by physical processes and are essential elements in assessing of the distribution dynamics of Chironomidae dipteran insects and their role in aquatic ecosystems. This work presents results of distribution patterns of chironomids larvae in 38 sites that are abundant in the study site, inhabiting the substrate of the main river channel, rapids, tributary brook, floodplain lakes and reservoir along the Sepotuba River from its mouth at the Paraguay River to the headwater region. A total of 1,247 larvae was registered. The most abundant taxa were Polypedilum (Tripodura) sp. (25.2%), Cricotopus sp.3 (23.0%) and Tanytarsus sp. (15.0%). Fissimentum desiccatum were found only in the reservoir; Fissimentum sp.2 and Tanytarsus cf. T. obiriciae sp.2 in floodplain lakes, and Goeldichironomus sp. in the main channel. The low diversity of the sites S06 and S35 is caused by the near-exclusive presence of the species Cricotopus sp.3, alone or together with one or another taxon (Tanytarsus sp., Djalmabatista sp.3). Collectors-filterers represent 16%, collectors-gatherers 15%, predators 11% and scrapers only 1%. The predators dominated in the secondary channel (±88 ind/m2), corresponding to 40% of the total of this group. Cryptochironomus sp.2 (34%) and Ablasbemyia gr. annulata (26%) were the most abundant among the predators. The differences along the river course are decisive for the formation of distinct or discontinuous communities and the limits become obvious though the interrelations between the populations in the community, as for instance, competition for food and habitats.

Consequences of dam construction upstream of the Upper Paraná River floodplain (Brazil): a temporal analysis of the Chironomidae community over an eight-year period.

Our study aimed to identify patterns of temporal variation and changes in the structure of the community of Chironomidae larvae in two rivers in the Upper Paraná River floodplain after the construction of a reservoir upstream (Porto Primavera). Samples were taken with a Petersen grab, and were obtained between 2000 and 2007. Chironomidae larvae were identified down to the lowest taxonomic level possible. The high richness of Chironomidae observed in the Paraná and Ivinhema Rivers (100 morphospecies) in comparison to the world average of rivers of the same size (44 species) emphasizes the importance of these habitats for the maintenance of biodiversity. The composition and density of Chironomidae in the years 2000 and 2001 differed from the other years. This period was characterized by extreme changes in the Paraná River flow caused by the closing of the Porto Primavera Dam, which added to a severe dry period in late 2001. The different compositions of morphospecies and the higher similarities in subsequent years are indicative of the recovery and adaptation of the community. In spite of the changes in the composition of morphospecies, diversity was maintained and the community continued to respond to fluctuations in the hydrometric level.

Consequences of dam construction upstream of the Upper Paraná River floodplain (Brazil): a temporal analysis of the Chironomidae community over an eight-year period / Conseqüências da construção de um reservatório a montante da planície aluvial do Alto Rio Paraná (Brasil): análises temporais da comunidade Chironomidae em um período de oito anos

Our study aimed to identify patterns of temporal variation and changes in the structure of the community of Chironomidae larvae in two rivers in the Upper Paraná River floodplain after the construction of a reservoir upstream (Porto Primavera). Samples were taken with a Petersen grab, and were obtained between 2000 and 2007. Chironomidae larvae were identified down to the lowest taxonomic level possible. The high richness of Chironomidae observed in the Paraná and Ivinhema Rivers (100 morphospecies) in comparison to the world average of rivers of the same size (44 species) emphasizes the importance of these habitats for the maintenance of biodiversity. The composition and density of Chironomidae in the years 2000 and 2001 differed from the other years. This period was characterized by extreme changes in the Paraná River flow caused by the closing of the Porto Primavera Dam, which added to a severe dry period in late 2001. The different compositions of morphospecies and the higher similarities in subsequent years are indicative of the recovery and adaptation of the community. In spite of the changes in the composition of morphospecies, diversity was maintained and the community continued to respond to fluctuations in the hydrometric level.

Este trabalho teve por objetivos identificar padrões de variação temporal e alterações ocorridas na estrutura da comunidade de larvas de Chironomidae de dois rios da planície aluvial do Alto Rio Paraná nos anos subseqüentes ao fechamento de um reservatório à montante, Porto Primavera. As amostras foram coletadas de 2000 a 2007 com um pegador do tipo Petersen, modificado. As larvas de Chironomidae foram identificadas até a menor categoria possível. A elevada riqueza de Chironomidae observada nos rios Paraná e Ivinhema (100 morfoespécies), quando comparada com a média mundial para rios de mesmo porte (44 espécies), ressalta a importância desses ambientes para a manutenção da biodiversidade. Tanto pela dominância, como também pela composição e densidade numérica, verificou-se que os anos de 2000 e 2001 diferiram dos demais. Este foi um período de fortes alterações no fluxo do Rio Paraná causado pela instalação do reservatório Porto Primavera aliado a uma grande seca ocorrida no final de 2001. Uma nova composição de morfoespécies e maior semelhança entre os anos seguintes são um indicativo da recuperação e adaptação da comunidade. Apesar das mudanças na composição de morfoespécies a diversidade foi mantida e a comunidade continua respondendo às flutuações do nível hidrométrico.