Linking transient dynamics and life history to biological invasion success

Abstract

Summary 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 study the dynamics of small ‘invading’ populations for 105 plant species spanning a range of life histories, including species classified as both invasive and non‐invasive. We simulated the matrix population models to estimate the effect of transient dynamics on population viability (i.e. potential invasiveness) after a hypothetical seed dispersal event into a novel environment. We then evaluated the predictive power of transient and long‐term population growth rates to explain variation in population viability and identified the life‐history correlates of population dynamics that best explained establishment success. 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 during establishment than either the rate of decline or transient ability to increase in density following a decline. Despite a negative correlation between transient density and fecundity, species with high fecundity had disproportionately favourable transient dynamics and higher long‐term population growth rates, resulting in higher population viability. 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 and help explain the common empirical finding that species invasiveness is correlated with fecundity. Synthesis. Transient and long‐term population dynamics are independent predictors of demographic performance that influence the viability of invading (i.e. small, unstable) populations subjected to strong effects of demographic stochasticity. Greater long‐term population growth rates and disproportionately favourable transient dynamics may account for the commonly observed invasiveness of highly fecund species. Given the strong dependence of population viability on population growth and the wide range of transient responses among species, transient analysis may provide critical insights into the demographic correlates of biological invasion potential.