Revisiting Elton’s copepods: lake construction has altered the distribution and composition of calanoid copepods in the British Isles

摘要

It is now widely accepted that the construction of new lakes, ponds and reservoirs facilitates the invasion of non-indigenous aquaticspecies, due largely to low biotic resistance from native communities. The role played by constructed waters appears to be aparticularly frequent feature of zooplankton invasions. Charles Elton, in his classic 1927 book “Animal Ecology”, noted that theestuarine calanoid copepod Eurytemora velox had invaded constructed inland waters in Britain and highlighted the lack of a keyspecies, Eudiaptomus gracilis, in allowing its establishment. At the time, Elton’s observations were dismissed and his findingslargely consigned to obscurity. Using occurrence records gathered since this time and current knowledge of calanoid copepodecology and invasion biology, we re-examined the distributions of three species of freshwater calanoid copepods in the BritishIsles to: 1) determine the legacy of lake and pond construction on their distributions, and 2) reassess the conclusions made by Eltonin light of this knowledge. The lack of natural lakes in the south and east of England, and the subsequent widespread developmentof new lakes and ponds, has altered calanoid copepod distributions. The common E. gracilis occurs frequently in the north andwest of the British Isles in natural lakes, and is found in the south and east in constructed waters. The estuarine E. velox was foundonly in 3 natural freshwater sites, all in close proximity to the coast, but has been recorded in 23 constructed sites, many of thesewell inland. Elton noted a general lack of co-existence between E. velox and E. gracilis, with the relatively slow establishmentrates of E. gracilis thought key in allowing the estuarine species to invade. However, subsequent collections suggest long-term cooccurrenceof these species at some sites. We suggest that E. velox has now successfully invaded freshwaters in the British Isles.Eudiaptomus vulgaris is not known from natural lakes, but has been recorded in several constructed waters, and appears to haveinvaded Britain facilitated by lake construction. Current knowledge supports Elton’s contention that constructed waters are morereadily invaded than natural waters, and that biotic resistance due to the presence of key species is important. While some specificcriticisms of Elton’s ideas were valid, we argue that Elton’s concepts regarding constructed waters and invasions were in manyways correct and prescient of current understanding.