Population and community macroinvertebrates characterization in ephemeral stream in north Patagonian perennial forest relict (Rucamanque, 38°S, Araucanía, Chile)

The benthic macroinvertebrates in Patagonian streams are characterized by the presence of abundant aquatic insect larvae stages and crustaceans that can be used as water quality bioindicators. The studied site is an ephemeral stream, present only during rainy season and located in Rucamanque, a north patagonian park that is a relict of pristine perennial forest located at the northwest side of Temuco city. Benthic macroinvertebrates were first studied at population level, considering the spatial distribution of the taxa reported to determine if macroinvertebrates have a random, uniform or aggregated pattern with respective Poisson, binomial and negative binomial distribution. As second step, data were studied at community scale using null models, based on random presence on species co-occurrence and niche sharing. The results revealed that taxa such as Nematoda, presented a random and in consequence a Poisson distribution, while other groups such as Neuroperlopsis sp. (Plecoptera order), Psephenidae (Diptera order) and Aegla sp. (Decapoda order) presented a uniform with binomial distribution, and species from Diptera order such as; Tipulidae, Simulidae, Chironomidae, from Plecoptera order such as Diamphinopsis sp., from Ephenoptera order such as Leptophlebiidae and Chiloporter sp, from order Trichoptera ( Smicridea sp) and Oligochaeta ( Tubifex sp.) presented an aggregated negative binomial distribution. The results of null models’ analysis revealed that species associations were random, whereas the taxa share niche due interspecific competition. The exposed results of spatial distribution and null models were similar to previous observations in other Patagonian pristine rivers. At population level, only Nematoda had random distribution whereas at community level the random presence of species co-occurrence is due the presence of low species number with many repeated taxa by sample, that also would have niche sharing.