Linking transient dynamics and life history to biological invasion success

Background/Question/Methods

Upon arriving in a novel environment, invading populations are likely to be small and far from a stable stage structure.  This unstable stage structure can cause transient (short-term) population dynamics to differ greatly from asymptotic (long-term) dynamics.  Because the persistence of small populations depends heavily on population growth rate, short-term dynamics may strongly influence the viability of invading populations.  We used published matrix population models to simulate population dynamics following introductions of seeds for 84 plant species spanning a range of life histories.  From demographic simulations, we estimated the effects of transient and long-term dynamics on population viability for each species.  We then identified the life history correlates of population dynamics that best explained establishment success.

Results/Conclusions

Transient and long-term population growth rates were positively but independently correlated with population viability across species.  Minimum transient density (minimum population density attained en route to a stable stage structure) was the best transient predictor of population viability.  This suggests that avoidance of severe short-term population declines is more important for establishment than either the rate of decline or ability to increase in density following a decline. Despite a negative correlation between transient density and seed number, species with high fecundity had disproportionately high transient densities and higher long-term population growth rates.  Together, these results suggest that highly fecund species are better equipped to overcome the early effects of demographic stochasticity in the establishment phase than less fecund species. This study therefore provides a mechanistic link between population dynamics theory and empirical studies finding that invasiveness is associated with high fecundity.