Aquatic Insect Herbivore Functional Community Traits Respond to a Different Niche Between a Riparian and Sugar Cane Leaf Litter Processing.

The niche of aquatic insect herbivores can be determined by the resource quality of leaf litter species. We compared the niche functional trait of aquatic insect herbivores between Magnolia ovata (riparian tree) and Saccharum officinarum (sugar cane) leaf litter processing. We hypothesized M. ovata and sugar cane leaf litter species would influence different functional traits niche of aquatic insect herbivores due to different quality resource leaves. We performed colonization experiments using dry leaves in five streams during 30-34 days. We utilized five replicates per leaf litter (n = 25) containing 12 g of dry leaves. We compared the niche specialization of herbivore functional traits using the Community Weight Mean (CWM) index and throughout herbivore abundance and the similarity composition of taxa. Additionally, we analysed the influence of organic matter in the CMW index of herbivore functional trait niche. We observed a higher abundance of shredders than scrapers in both leaf litter species. The M. ovata leaf litter selected a more specialized niche of respiration trait composed mainly chironomid shredder larvae, with the osmotic mechanism. The community structure differs weakly with a stronger and positive relationship between organic matter and respiration CWM index in riparian than sugar cane leaf litter. Concerning different composition communities between leaf plants, we consider that aquatic insect herbivore demonstrates a preference to leaf litter species with a specific resource. Additionally, most taxa adapt their feeding habit dependent on the availability of resource food.

Shredder Chironomid Diets Are Influenced by Decomposition Rates of Different Leaf Litter Species.

The diet of shredder chironomid larvae depends on the local and temporal conditions of the food resources. We analysed the gut content of shredder chironomid larvae that colonised the leaf litter of three riparian species: Hedychium coronarium, Pteridium arachnoideum and Magnolia ovata. We hypothesised that the differences in the decomposition rates of leaf litter species influence the consumption of plant tissue by shredder chironomid taxa over time. We incubated perforated bottles with each leaf species within four low-order streams during 1st, 3rd, 7th, 22nd, 36th, 55th and 85th day of exposure. We used an analysis of covariance (ANCOVA) to compare differences in the percentage of AFDM (ash-free dry mass) and AOM (amorphous organic matter) among leaf litter species. To verify differences in the larvae abundance, we used a general linear model, and to test if there were feeding preferences for AFDM and AOM, we used the adapted Paloheimo selectivity index. Magnolia ovata presented a higher quantity of AOM followed by H. coronarium and P. arachnoideum. Pteridium arachnoideum showed a higher AFDM followed by H. coronarium and M. ovata. The larvae abundance was different among plant species and varied significantly with AFDM and AOM quantities. The consumption of plant tissue by shredder chironomid differed temporarily and among riparian species, where facultative or strict shredders showed strong association with different leaf litter species. The amount of AFDM and AOM in plant tissues explained these differences. We highlighted that shredder chironomids displayed an important role as co-participants in the decomposition process.

Body Length Determines the Diet and Niche Specialization of Non-Biting Midge Predator (Tanypodinae) Larvae in Shallow Reservoirs.

The functional traits of species respond to environmental gradient changes, which, in turn, are responsible for the niche specialization of species. We analyzed the niche specialization of several Tanypodinae taxa (predatory non-biting midge, 4th instar, n = 693) along the depth zones of the water in six shallow tropical reservoirs. We measured the body length and diet composition of seven Tanypodinae larvae genus. Community-weighted mean (CWM) traits index was utilized to calculate the niche distribution of body length and diet composition. We analyzed the niche distribution of predator larvae, through a simple linear analysis of CWM index and the depth of the water, and by establishing correlations between body length and diet composition. In our study, it was found that the consumption of oligochaete (b = 0.30, SE ± 0.04, t = 7.02, p = 0.0001, R2 = 0.45) and the body length (b = 0.64, SE ± 0.11, t = 5.44, p = 0.0001, R2 = 0.33) increased in deeper zones. We observed a strong and positive relationship between oligochaete consumption and a longer body (r = 0.91, p = 0.0001). We inferred that changes in habitat characteristics, from littoral to deeper zones of the reservoirs, are expected to have influenced the selection of larvae traits predators. We concluded that body length determines the diet consumption and accurately reflects the niche distribution of Tanypodinae assemblages. The functional trait approach proved to be an efficient tool for the analysis of the ecological processes that determine the structure of a non-biting midge predator assemblage.

Aquatic insect community structure under the influence of small dams in a stream of the Mogi-Guaçu river basin, state of São Paulo.

The fragmentation of lotic systems caused by construction of dams has modified many aquatic communities. The objective of this study was to analyse changes in the aquatic insect community structure by discontinuity of habitat created by dams along the Ribeirão das Anhumas, a sub-basin of the Mogi-Guaçu River (state of São Paulo, Brazil). Entomofauna collection was carried out in 10 segments upstream and downstream of five dams along the longitudinal profile of the stream, with a quick sampling method using a D net (mesh 250 mm) with 2 minutes of sampling effort. The insects were sorted and identified to the lowest possible taxonomic level and analysed by the Shannon diversity index, ß diversity, richness estimated by rarefaction curves and relative participation of functional feeding groups. The results showed a slight reduction in diversity in the downstream segments, as well as along the longitudinal profile of the stream. However, there were no significant differences in abundance and richness between the upstream and downstream segments, indicating that the dams did not influence these variables. Differences were observed in the functional feeding groups along the longitudinal profile. Predator and gatherer insects were dominant in all segments analysed. The feeding group of shredders was more abundant in the segment DSIII with the participation of Marilia Müller (Odontoceridae - Trichoptera), although we observed a decrease of shredders and scrapers with the decrease of the canopy cover reducing values of ß diversity in the continuum of Ribeirão das Anhumas. This result demonstrated the importance of the conservation of the riparian vegetation in order to maintain the integrity of the stream.