Ecological and evolutionary determinants of continental-scale variation in demography and population growth rates of a rapid European plant invader

Background/Question/Methods

Invasion dynamics ultimately depend on how reproduction, mortality and growth are shaped by abiotic and biotic conditions as well as adaptive and non-adaptive evolution in the past. In a continental-scale study, we quantified these key demographic quantities for 1287 marked individuals in 22 European invasive populations of the South-African Ragwort (Senecio inaequidens). We then analyzed how demographic variation is affected by climate, inter-specific competition, genetic Allee-effects, population relatedness and population age. By the means of Integral Projection Models we analysed how differences in individual demographic performance translate in continental-scale variation in population growth rates.

Results/Conclusions

Our results suggest that growth and reproduction are subject to genetic Allee-effects and decrease with population age. As population relatedness influences growth under natural conditions, population dynamics may fluctuate stochastically. Furthermore, growth and survival are affected negatively by rainfall and growing degree days. Our study clearly shows that invasive plant populations are not equal and identifies drivers of continental-scale demographic variation. The population models demonstrate that this systematic among population variation in demographic rates affects population growth and thus invasion dynamics. Such demographic understanding is crucial for predicting the future range dynamics of both invasive and native species.