Success of the invasive Ponto-Caspian amphipod Dikerogammarus villosus by life history traits and reproductive capacity

Dikerogammarus villosus originates from the Ponto-Caspian basin. In the Austrian stretch of the River Danube it was not found before 1989, and not before 1992 in the Bavarian Danube. It very quickly spread to Germany, the Netherlands, and France via the so called Southern Corridor. The invader also migrates via the Central Corridor, reaching as far west as the Vistula River. The species has been reported from a number of lakes. Reasons for the quick spread and high abundance are, beside others, its life history traits. A population of this invasive species was studied from 2002 to 2004 in the Austrian stretch of the Danube. The following life-history traits are important in the invasion success: long reproductive period, early sexual maturity, short generation time, a life span not exceeding 1 year (up to three generations and 14 cohorts being present at the same time), high growth rates resulting in large body size, short duration of embryonic development, large numbers of comparatively small eggs in the brood pouch, large reproductive capacity, and optimal timing to release the maximum number of neonates per female in May/June (maximising rapid growth at high summer temperatures and at times of plentiful food), increasing mating privilege for large specimens of both sexes with decreasing water temperatures during winter. These life cycle characteristics together with its predatory behaviour and its ability to cope with variation in oxygen, temperature and salinity, give this invader a potential to become distributed in freshwater ecosystems of the temperate climate zone all over the world. Additionally, several indications seem to prove the tendency that biological invasion and global warming have a positive feed-back on each other. This combined scenario is a huge threat to the indigenous aquatic fauna, and might contribute to bio-monotony.