Population and community characterization of macroinvertebrates in an ephemeral stream within a North Patagonian perennial forest relict (Rucamanque, 38°S, Araucanía, Chile).

Benthic macroinvertebrates inhabiting Patagonian streams are characterised by abundant aquatic insect larvae and crustaceans that may serve as valuable bioindicators of water quality. The present study was conducted in an ephemeral stream located within the Rucamanque forest, a pristine North Patagonian perennial forest relict situated near Temuco city, southern Chile. Macroinvertebrates were first analysed at the population level by examining the spatial distribution of individual taxa in order to determine whether their distribution patterns were random, uniform or aggregated, corresponding respectively to Poisson, binomial and negative binomial distributions. Subsequently, the assemblage was analysed at the community level using null models based on species co-occurrence and niche overlap. The results revealed that Nematoda exhibited a random spatial distribution associated with a Poisson model, whereas Neuroperlopsis sp. (Plecoptera), Psephenidae (Coleoptera) and Aegla sp. (Decapoda) showed uniform distributions consistent with a binomial model. By contrast, Tipulidae, Simuliidae and Chironomidae (Diptera), Diamphipnopsis sp. (Plecoptera), Leptophlebiidae and Chiloporter sp. (Ephemeroptera), Smicridea sp. (Trichoptera), and Tubifex sp. (Oligochaeta) displayed aggregated spatial distributions fitted by a negative binomial model. Null model analyses indicated that species co-occurrence patterns were random, whereas niche overlap analyses suggested significant niche sharing among taxa. The observed spatial distribution patterns and community structure were consistent with previous reports from other pristine Patagonian river systems. At the population level, only Nematoda displayed a random distribution pattern, whereas at the community level the apparent random species co-occurrence may be explained by the low number of taxa recorded and the repeated occurrence of the same taxa across samples, which may also promote niche sharing.