Life history traits as predictors for biological invaders

Invasive species have often been said to display r-selected traits. However, when ecologically similar species are already established, interspecific competition rather than the ability to colonize or rapidly grow in numbers at low density could be the limiting factor of invasion, favouring K rather than r traits. We tested this idea using the "invasive series" approach. We define an invasive series as a suite of ecologically and/or taxonomically similar taxa invading the same region, characterised by hierarchical invasive ranks, in terms of ability to competitively displace each other and become numerically dominant in the invaded area. Three species of polyphagous fruit flies (Diptera: Tephritidae) that successively invaded the Reunion Island (initially occupied by a fourth, endemic species) together provide an example of such a series. We characterized life-history traits of these four species in optimal laboratory conditions, at all stages from egg to death in order to test whether invasive ranks were dependent on positions along an r-K gradient. Our results suggest an interspecific trade-off between K and r traits, and that the K lifestyle is associated with higher ranks in the invasive series. The resident endemic species is an exception, as it has low values for both r and K traits. Its competitive exclusion by the three invasive species is therefore explained by some form of maladaptation rather than by a strategy along an r-K trade-off. (Texte integral)