Invertebrate colonization of a new, man‐made stream in southern Sweden

Abstract

SUMMARY. The invertebrate colonization of a man‐made stream, Flugströmmen, in southern Sweden was monitored for 18 months in 1988 and 1989. Benthic samples were taken on twelve occasions from three sites (upstream, middle and downstream) and community structure was compared with that at ten natural, permanent reference sites nearby. The number of species colonizing increased rapidly during the first 3 months. The increase was most rapid upstream but levelled off during the second year at this site, while numbers continued to increase downstream. Simuliid species were the earliest colonizers and reached high densities at upstream and middle sites during the first year. Ephemeropteran and plecopteran species also occurred early on, whereas Coleoptera, Odonata and Trichoptera were, on average, slower to colonize. Blackfly densities decreased upstream after the first year and hydropsychids became numerically dominant. The colonization order of functional feeding groups was as predicted: filter feeders first, grazers/collectors intermediate, predators and shredders last. After a year, the community structure in Flugströmmen closely resembled that in lake‐outlet streams situated in the area, although communities at the three sites within the stream were most similar to one another. The possible role of competitive and predatory processes in determining the observed successional patterns are discussed.