Feeding strategies are typical traits reflecting the adaptation of species to environmental conditions. This concept is currently developed in some water quality systems (e.g. Index of Trophic completeness) and the structure of functional feeding groups (FFGs) could form part of a unified measure across communities differing in taxonomic composition. However, in South America, information about the FFG classification of invertebrates in streams is almost absent and existing studies using FFG structure follows classification from North America. But even taxonomically related species may have different diets in tropical and temperate areas and therefore, studies about FFG structure in neotropics could be biased. For this reason, we determined diet composition, trophic level and FFGs, using gut contents analysis and mouthpart observations of 49 macroinvertebrate taxa (mostly at genus level) from neotropical streams. We observed that practically all macroinvertebrates fed upon fine detritus which indicates the importance of this food resource in neotropical streams. As the assignment to a single FFG does not accurately reflect the functional profile of taxa, we transcribed the affinity of taxa to each FFG using fuzzy codes. Finally, we published the coding of diet composition and FFG of the taxa examined, which could be used in future community analyses of lotic ecosystems in the Neotropical zone.
SUMMARY 1. Using experimental streams, we studied the impact of the crayfish Orconectes limosus on (i) the transport of gravel and sand at baseflow; (ii) the sediment surface (bedform, particle consolidation, proportion of sand, algal and gravel cover); and (iii) the critical shear stress (τC) causing incipient gravel and sand motion during simulated floods. We examined (i) and (ii) in experimental outdoor flumes that replicated riffle‐pool sequences and (iii) in a larger laboratory flume, in which we exposed sediments retrieved from the outdoor flumes to a progressively increasing discharge. 2. Habitat changes induced by crayfish, such as bedform alterations in riffles (downstream displacement of riffle heads) and the increase of gravel on sand dunes in pools, had major impacts on the spatial and temporal patterns of the baseflow transport of gravel and sand. 3. In addition to their impact on bedform in riffles and on gravel cover in pools, crayfish prevented the physical consolidation of particles in riffles and reduced the algal cover and the proportion of sand in the surface layer in both riffles and pools. These crayfish impacts on sediment surface variables had complex, interacting effects on the mobilisation of gravel and sand during subsequent flood simulations. For sand, crayfish progressively decreased the τC (i.e. the sum of bedform drag and skin friction) by about 50% along the entire biomass gradient in pools, whereas the presence of crayfish abruptly decreased the τC by about 75% in riffles. For gravel, the discharge causing motion in riffles produced a shear stress (in terms of skin friction) on an even bedform that was about 75% lower in all flumes with crayfish compared with the flumes without crayfish. Crayfish had no impact on τC for gravel in pools. 4. Scaling‐up these experimental results to real streams suggests that crayfish could affect the patch dynamics of major sediment transport events and habitat suitability for other organisms that, at larger spatial scales, could increase the overall spatio‐temporal habitat diversity and thus the overall structural and functional biodiversity of lotic communities.
The River Continuum Concept (RCC) explains the structural and functional characteristics of stream communities focusing on the gradually changing physical components from headwaters to downstream habitats of streams and rivers. The global value of the RCC is still uncertain, possibly because physical factors (e.g., altitude and then temperature, stream order, channel width) can vary differently in longitudinal river axes across the world. Moreover, RCC predictions in relation to different physical factors have not been tested adequately in different biomes, especially biomes outside of temperate North America. Here, we report on the functional structure of macroinvertebrate communities in neotropical streams from Bolivia along a broad altitudinal gradient (from 1120 to 4300 m a.s.l.), aiming to understand how altitude can affect the longitudinal changes in functional feeding groups (FFG) and richness predicted by the RCC. The RCC predictions for functional structure were not completely matched when analyzing FFGs in relation to an index of longitudinal stream gradient. However, after removing the effect of altitude by using residuals from regressions between FFGs and altitude, FFG patterns matched RCC predictions more closely. We detected signifi cant relationships between altitude and the relative abundance of collector-gatherers, shredders and scrapers which may be related to changes in temperature, UV radiation and canopy cover along the altitudinal gradient. Our results indicate that altitude combined with position along the longitudinal gradient is an important factor governing the FFG structure of macroinvertebrate communities in neotropical streams.
We developed a preliminary macroinvertebrate-based multi-metric index to assess streams biotic condition in the Upper Isiboro-Sécure basin (Bolivia). To do so we used eight local habitat descriptors and twelve metrics describing the structure and function of macroinvertebrate assemblages from 38 reference and 29 disturbed sites. Stepwise multiple linear regression procedures were first applied using the reference data to elaborate models describing metrics response to natural environmental in the absence of any significant disturbance. In a second step we used residuals distribution of each of the twelve models to select the most effective metrics in discriminating between reference and disturbed sites. These metrics were: number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), abundance of EPT, relative abundance of EPT, abundance of Chironomidae and relative abundance of Chironomidae. Finally, after converting residual values of these 5 remaining metrics into probabilities, we added values to obtain a final index score and interpreted this score as excellent, good, moderate, poor or very poor. Our final multi-metric index distinguished well between natural and humaninduced variation in biological condition and showed a significant negative response to a gradient of disturbances. This type of approach could be used in the near future to develop a nation wide index by increasing regional-scale monitoring.
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