POPULATION-DYNAMICS OF 2 COLLEMBOLAN SPECIES IN AN ARCTIC TUNDRA

Population dynamics of Folsomia qundrioculata (Tullberg) and Hypogastr ura tullbergi (Schaffer) have been studied during foul years in a Cass iope-heath close to Ny-Alesund, Svalbard. The study area was sampled a t three different sites of similar vegetation. The density of F. quadr ioculata appeared to fluctuate less between years th;ln did the densit y of H. tullbergi. The latter species showed significant winter mortal ity and a reproductive period in early summer only. The coldest summer appeared to have the largest effect on the densities of H. tullbergi. F. qundrioculata did not show significant winter mortality and reprod uced throughout the two summers when reproductive activity was investi gated. Individual specimens of F. quadrioculata apparently reproduce d uring one summer only since adult specimen decreased in density from m id-to late summer and high recruitment coincided with high adult morta lity. H. tullbergi most likely requires two summers to complete develo pment from egg to adult. However, due to the synchronised reproduction in early summer, individuals of this species will not reproduce befor e their third summer. The life cycles and dynamics of the species are discussed in relation to their distribution and abundance at Svalbard.