The vicinity of reservoirs and type of environment contribute to the occurrence of an exotic cladoceran, Daphnia lumholtzi (Sars, 1885), in a Neotropical drainage basin

Biological invasions are one of the major threats to the integrity of aquatic ecosystems worldwide. We examined the influence of reservoirs, availability of food resources, abiotic resistance, and biotic resistance on the distribution of Daphnia lumholtzi, a non-native cladoceran that is spreading through habitats in the upper Paraná River basin, Brazil. We sampled 48 sites distributed in four habitat types: reservoirs, lakes, tributaries, and the main river. D. lumholtzi densities were higher in reservoirs than in other habitat types (lentic and lotic). We found a significant correlation between a higher density of D. lumholtzi and the distance from reservoirs to the other sampling points. Additionally, a relationship between D. lumholtzi and types of environments was noted. It is known that cladocerans, including D. lumholtzi, have a reduced swimming ability, which makes it difficult for them to overcome currents and consequently establish or maintain large populations in lotic environments. Further research is needed to identify other factors responsible for the species' occurrence in this system and to determine the possible effects this species may have on the native community.