Invasive non-native (alien) species are considered to be one of the greatest threats to biodiversity (Millenium Ecosystem Assessment 2005) through predation, competition, hybridisation or as vectors of disease (Hulme et al., 2009). The movement of peole and goods is increasing the rate of invasive alien species arriving in countries around the globe. A recent inventory of alien species in Europe revealed a figure of 11000 species (Hulme et al., 2009) but it is recognised that this is a first approximation and likely to be an underestimate (Olenin & Didžiulis, 2009). The distinction between native species and alien species is problematic; species have been moving around the world over millennia and the origin of many species is uncertain. It is also evident that many archaeophytes and archaeozoans establish within native communities without detrimental effects on species and ecosystem processes (Pyšek et al., 2005). However, the small proportion of alien species that are problematic (invasive) are both ecologically and economically costly (Hulme et al., 2009). Furthermore, historically species movements have occurred within continents but in recent decades an increasing proportion of alien species are from other continents (Hulme et al., 2009). Alien species originating from within a continent are predicted to be less invasive than those from other continents (Hulme et al., 2009)
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