Coexistence and life cycle characteristics of five species of the amphipod genus Gammarus

The life cycle characteristics of five amphipod species of the genus Gammarus: G. oceanicus, G. locusta, G. salinus, G. zaddachi, and G. duebeni from a Danish brackish water area are given, and discussed in relation to coexistence between the species. The five species are distributed according to salinity and with more or less narrow zones of overlap. The species that do overlap in distribution always have diametrically different life cycles so that the three winter breeding forms (G. duebeni, G. salinus, and G. oceanicus) are separated by the two summer breeding forms (G. zaddachi, G. locusta). These findings are discussed in terms of size differences between coexisting species populations and interspecific precopulation.