Resource availability influences the flow of energy through food webs, thus affecting biomass and trophic structure of consumer communities. To assess the effect of availability of allochthonous (leaf litter) and autochthonous (periphyton) resources on the trophic structure of macroinvertebrates, we sampled monthly for a year two sites (upstream forested, downstream open canopy) of Challhuaco, a low order mountain stream in the Patagonian Andes. Leaf litter and periphyton dynamics showed the expected pattern, peaking in autumn and spring, respectively. Temporal variations of shredders and scrapers were synchronized, with the logic delay, with resource abundance. Although leaf litter mass was similar at both stream reaches, shredders were more abundant at the forest site. Periphyton biomass was higher at the forest, while scrapers were more abundant at the open site. The patterns of resource and consumer abundance, and community functional structure were mostly explained by the interaction of abiotic factors and trophic relationships.

The macroinvertebrate fauna of twenty-one ponds (thirteen temporary and eight permanent) located in four protected areas in Central Italy were studied in March, May and June 2002, with the aim to bring out relationships between environmental variables and the functional characteristics (functional feeding groups, habits and resistance to drought) of communities. Macroinvertebrates were collected in three mesohabitat types (macrophyte beds, littoral sediments, central sediments). Overall, the functional attributes of temporary and permanent pond communities did not differ greatly. However, at the mesohabitat scale, collector-gatherers, burrowers and permanent residents capable of passive dispersal were more abundant in sediments. Scrapers and shredders, sprawlers and climbers, swimmers and divers, and organisms capable of active dispersal which lack drought resistance were more abundant in macrophyte beds. Although hydroperiod is the main driving factor affecting community structure, our results suggest that it remains an unimportant factor in controlling functional traits, which appeared to be more influenced by substratum types. Moreover, the positive relationship between taxonomic and functional diversity metrics indicates that an increase in taxonomic richness induces a satisfactory partitioning of the ecological resources among taxa, thus maintaining the ecological complexity of the ponds regardless of their hydroperiod length.

The composition and abundance of functional feeding groups of the macroinvertebrate communities were investigated alongthe Chubut River in the Patagonian Precordillera and Plateau, Argentina. Chubut River (>1000 km) is the largest river in the area and the hydrological regime is modified in the lower section by an artificial reservoir (Florentino Ameghino Dam). Quantitative benthic samples were collected at 13 sites in the upper, middle and lower sections of the river basin. Sites were visited four times during 2004 and physicochemical parameters, chlorophyll a and particulate organic matter (POM) were assessed. In terms of relative abundance, collector-gatherers and scrapers/grazers were the predominant groups at most sites. Shredders were not abundant in the upper sites and were practically absent at middle and lower basin sites. Collector filterers that comprised morethan 25 % of abundance at the pre-regulated site were practically absent right below the dam. POM biomass decreased significantly with distance from the source and chlorophyll a showed a marked increase below the reservoir. We conclude that although there was a distinct headwaters fauna in the Chubut River, and sequential downstream changes in species composition, most functional feeding groups (apart from shredders) were represented down the whole length of the river. Finally, the usefulness of biotic indices and metrics in relation with main environmental features of the Chubut River basin is discussed.

L'étude a été réalisée début mai et fin juin 1994 dans 19 stations : 12 au long du cours principal et 7 au niveau de sources ou d'importants affluents. Les richesses taxonomique et spécifique (principalement Mollusques, Ephéméroptères, Plécoptères, Coléoptères et Trichoptères) montrent une évolution semblable avec un maximum à l'aval. L'analyse biotypologique par A.F.C. sur 68 espèces distingue 4 zones : le haut cours incluant les sources et les affluents montagnards, une zone de transition, une section moyenne très homogène avec les bas cours des principaux affluents malgré des perturbations polluantes et un bas cours à l'aval de deux barrages-retenues. Trois assemblages faunistiques majeurs se dégagent : un d'espèces du crénon-rhithron, un d'espèces plutôt eurytopes et thermophiles, et un d'espèces potamo-limnophiles. La zone de transition se définit alors par les deux assemblages entre lesquels elle se situe. Sur cette base typologique, la prise en compte des groupes trophiques montre que, seule, la basse Moulouya ne s'inscrit pas dans le schéma fonctionnel du 'R.C.C.'. La discontinuité observée à l'aval est probablement due aux effets des barrages (réduction du débit et de la largeur du lit), mais aussi au fait que cette section du fleuve retrouve un caractère plus naturel (ripisylve moins dégradée).

A study on sandy bottom macroinvertebrates in two moderately polluted stations of the River Treia (Central Italy) was carried out in order to analyze their structural and functional feeding organization. A total of 60 taxa were collected during the study. Oligochaeta, Gammaridae, Diptera-Chironomidae and Ephemeroptera constituted the bulk of the total fauna. Most of the taxa were typical of sandy bottom habitats and moderate current flow. Collectors and shredders were the dominant feeding groups in both stations. Predators were strongly and positively correlated with the abundances of collectors and shredders (potential prey). Moreover, the direct relationships found between taxonomic and trophic diversities or between taxonomic and trophic evenness suggest a relatively good partitioning of food resources among the taxa. The most common organisms found in both stations were typical of mesosaprobic environments, indicating that the macrofauna of fine sediments seems to be suitable for detecting moderate organic pollution in rivers.