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Pathways in Animal Invasions 25
advantage over the European pond turtle due to their lower age at maturity,
higher fecundity, larger adult body size, and more aggressive behaviour
(Cady and Joly 2004).
The goldfish (Carassius auratus) and related species, native to Central and
Eastern Asia, are favourite fish for aquarium and garden ponds, and have
reached a global distribution. They regularly escape or are released, have a
high reproduction rate, and today populate most European waters. As general
predators with highly flexible behaviour, they reduce biodiversity and change
ecosystem structure (Lehtonen 2002). Also North American pumpkinseed
species (Lepomis auritius, L. gibbosus) have been released into European
waters because of their colourful appearance and their attractive breeding
behaviour.
2.4 Conclusions
The main conclusions of this short presentation focus on the high variety of
pathways for the introduction of alien species. All pathways are linked to or
caused by human activities and, for many species, several pathways or combinations
of pathways are realised. Many introductions show astonishing historical
roots but globalization is a main driver of the actual acceleration of
invasion processes. When reading the wealth of information dealing with the
introduction of invasive alien species, one can argue that basic ecological
knowledge or, at least, common sense must have been weakly developed at
one point in time, and one would expect that the negative experience of the
past can largely be avoided today. However, there are present invasion events
which are even worse than those from past experience. The overall conclusion,
therefore, can only be that we need much tighter control, stricter quarantine
measures and more caution when shipping species and goods around the
world. These control costs are obviously well-invested money to prevent
much higher ecological and economical follow-up costs.
Acknowledgements. I would like to thank Cecily Klingler for valuable comments on
this chapter. My studies on invasive alien species have been considerably supported by
funding of the European Union within the FP 6 integrated project ALARM (GOCE-CT-
2003-506675) and by the specific targeted research project DAISIE (SSPI-CT-2003-
511202), which is gratefully acknowledged.