Anpassungsfähigkeit indigener und nichtindigener Arten an Umweltstressoren

Abstract

Successful invasive species are often hypothesized to have a wider ecological tolerance and consequently a reduced sensitivity towards a variety of stressors as compared to local species. Thus, part of the competitive hierarchy between invaders and native species may depend on the stress regime. Another factor of successful invasions is the reproductive potential of a species. The alien amphipod Gammarus tigrinus is a recent successful invader in the northern Baltic Sea and occupies comparable ecological niches and has similar reproductive periods in summer as the native Gammarus zaddachi in littoral ecosystems. In laboratory experiments, we determined the tolerance towards heat stress and hypoxia for the two competing species by exposing them to temperatures between 30°C and 35°C (heat stress) and only 1% dissolved oxygen at 20°C (hypoxia). For all stress tolerance experiments the response was measured as LT50, i.e. the time until mortality reached 50%. In separate experiments, we measured the fecundity of both species by counting their newly hatched juveniles. Gammarus tigrinus were more resistant to hypoxia, survived at higher temperatures and produced more juveniles than corresponding Gammarus zaddachi indicating wider tolerance ranges as well as a higher fecundity of the invasive species and maybe also competitive advantages above the native species