Can life-history traits predict the fate of introduced species? A case study on two cyprinid fish in southern France

1. The ecological and economic costs of introduced species can be high. Eco logists try to predict the probability of success and potential risk of the establishment of recently introduced species, given their biological chara cteristics. 2. In 1990 gudgeon, Gobio gobio, were released in a drainage canal of the R hone delta of southern France. The Asian topmouth gudgeon, Pseudorasbora pa rva, was found for the first time in the same canal in 1993. Those introduc tions offered a unique opportunity to compare in situ the fate of two close ly related fish in the same habitat. 3. Our major aims were to assess whether G. gobio was able to establish in what seemed an unlikely environment, to compare populations trends and life -history traits of both species and to assess whether we could explain or c ould have predicted our results, by considering their life-history strategi es. 4. Data show that both species have established in the canal and have sprea d. Catches of P. parva have increased strongly and are now higher than thos e of G. gobio. 5. The two cyprinids have the same breeding season and comparable traits (s uch as short generation time, small body, high reproductive effort), so bot h could be classified as opportunists. The observed difference in their suc cess (in terms of population growth and colonization rate) could be explain ed by the wider ecological and physiological tolerance of P. parva. 6. In conclusion, our field study seems to suggest that invasive vigour als o results from the ability to tolerate environmental changes through phenot ypic plasticity, rather than from particular life-history features pre-adap ted to invasion. It thus remains difficult to define a good invader simply on the basis of its life-history features.