The Role of Propagule Pressure, Genetic Diversity and Microsite Availability for Senecio vernalis Invasion

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.

Benefits of increased colonist quantity and genetic diversity for colonization depend on colonist identity

“…C or F) tended to perform comparatively poorly in isolation (genotype C also exhibited the lowest persistence in the mixed treatment; Supplementary material Appendix 1 Table A1), and thus overall performance of the species improved when the colonist pool was instead comprised of multiple genotypes. These results are similar to other studies that have indicated that the effect of increasing genetic diversity could depend upon the performance of particular genotypes (Vellend et al 2010, Erfmeier et al 2013, Hovick and Whitney 2019, highlighting how the traits of the genotypes in a small or low diversity population could determine its likelihood of success. If the population is comprised of high-performing genotypes (in the case of our experiment those with a high r), then higher genetic diversity is not necessarily required for success and including other poor-performing genotypes may reduce overall species performance.…”

“…While we know both quantity-and genetic-related mechanisms can be involved in the effect of colonist number on success, there is considerable uncertainty across studies in the separate and relative importance of these mechanisms. For many species, increasing either the quantity or genetic diversity of colonists proves beneficial (Ahlroth et al 2003, Memmott et al 2005, Hufbauer et al 2013, Szűcs et al 2014, Vahsen et al 2018, but others exhibit no benefits when quantity (Drake et al 2005, Fauvergue et al 2007, Crawford and Whitney 2010, Sinclair and Arnott 2017 or genetic diversity are increased (Hovick et al 2012, Erfmeier et al 2013, Robinson et al 2013. Determining what is causing this variability is key to improving our understanding of how the number of colonists affects colonization success, and for informing practical efforts that focus on controlling the colonization process to promote or prevent establishment and growth.…”

Coarse Woody Debris as a Land Reclamation Amendment at an Oil Sands Mining Operation in Boreal Alberta, Canada

“…In addition, non-native species were reduced with Low CWD of 1%-30% coverage, which indicates that even small amounts of CWD can have an immediate positive impact on the plant community. Non-native plants on No CWD plots were likely more abundant there due to bare ground providing microsites for germination, lack of competition (particularly in PMM), and elevated soil temperature which would favor these ruderal type non-native weed species with short life cycles [20,21]. These favorable conditions are reduced with CWD application, which likely leads to a subsequent reduction in non-native species.…”

Genetic and demographic founder effects have long‐term fitness consequences for colonising populations

“…) have shown that both the numbers of founders (Erfmeier et al . ; Wootton & Pfister ; Szűcs et al . ) and their genetic background (Crawford & Whitney ; Hufbauer et al .…”

“…Since more individuals typically harbour greater genetic diversity, only experiments in which both demography and genetics are manipulated simultaneously can decouple the relationship and reveal potential interactions between the two. The few studies of this kind (reviewed in Sz} ucs et al 2014) have shown that both the numbers of founders (Erfmeier et al 2013;Wootton & Pfister 2013;Sz} ucs et al 2014) and their genetic background (Crawford & Whitney 2010;Hufbauer et al 2013) can affect establishment success separately, or in combination (Ahlroth et al 2003;Hedge et al 2014) during the first and second generations. Only one study has followed colonising populations multiple generations after founding (Wootton & Pfister 2013), and none has yet tested explicitly how these factors and their interactions might affect colonisation of a novel environment.…”