Abstract
Genetic diversity is supposed to support the colonization success of expanding species, in particular in situations where microsite availability is constrained. Addressing the role of genetic diversity in plant invasion experimentally requires its manipulation independent of propagule pressure. To assess the relative importance of these components for the invasion of Senecio vernalis, we created propagule mixtures of four levels of genotype diversity by combining seeds across remote populations, across proximate populations, within single populations and within seed families. In a first container experiment with constant Festuca rupicola density as matrix, genotype diversity was crossed with three levels of seed density. In a second experiment, we tested for effects of establishment limitation and genotype diversity by manipulating Festuca densities. Increasing genetic diversity had no effects on abundance and biomass of S. vernalis but positively affected the proportion of large individuals to small individuals. Mixtures composed from proximate populations had a significantly higher proportion of large individuals than mixtures composed from within seed families only. High propagule pressure increased emergence and establishment of S. vernalis but had no effect on individual growth performance. Establishment was favoured in containers with Festuca, but performance of surviving seedlings was higher in open soil treatments. For S. vernalis invasion, we found a shift in driving factors from density dependence to effects of genetic diversity across life stages. While initial abundance was mostly linked to the amount of seed input, genetic diversity, in contrast, affected later stages of colonization probably via sampling effects and seemed to contribute to filtering the genotypes that finally grew up. In consequence, when disentangling the mechanistic relationships of genetic diversity, seed density and microsite limitation in colonization of invasive plants, a clear differentiation between initial emergence and subsequent survival to juvenile and adult stages is required.
Highlights
Genetic diversity within species and populations has been proven to have profound impacts on ecosystems by affecting community structure, nutrient fluxes and productivity, thereby affecting biotic interactions, such as resistance to disturbance and invasions [1,2,3]
Container experiment I – Propagule pressure and genetic diversity In the first experiment, we studied the role of propagule pressure, i.e. seed density, and genetic diversity for establishment of S. vernalis
Initial abundance of S. vernalis increased with increasing seed density level, with significant differences among all seed density levels (Table 1, Fig. 1A)
Summary
Genetic diversity within species and populations has been proven to have profound impacts on ecosystems by affecting community structure, nutrient fluxes and productivity, thereby affecting biotic interactions, such as resistance to disturbance and invasions [1,2,3]. In recent years, studies on the role of genetic variation in biological invasions have shown that the maintenance of high genetic diversity is a feature of successful invasions [7,8,9,10], genetic diversity has rarely been experimentally addressed to explain invasiveness of species despite some evidence of both additive and non-additive effects of genetic diversity on colonization success [7,11,12,13]. High within-population genetic diversity might enhance coexistence of individuals, since fitness might be positively influenced if individuals are functionally different. Such complementarity effects are based on optimized resource use if assessed at the community level [17] and can lead to increased overall productivity [18]
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