Invasion genetics
[1] Stebbins, working with another botanist, Herbert G. Baker, collected a series of articles which emerged from the Asilomar symposium and published a volume titled The Genetics of Colonizing Species in 1965.
In 1992, the ecologists Mark Williamson and Alastair Fitter divided the process of biological invasion into three stages: escaping, establishing, and becoming a pest.
[7] Since then, there has been an expanding effort to develop a framework for categorizing biological invasions in terms that are neutral with respect to a species' environmental and economic impacts.
David M. Richardson and colleagues describe how introduced species must pass a series of barriers prior to becoming naturalized or invasive in a new range.
[9] The most recent systematic effort to describe the steps of a biological invasion was made by Tim Blackburn and colleagues in 2011, which combined the concepts of barriers and stages.
As early as 1955, Herbert G. Baker proposed that self-fertilization would be a favourable trait for colonizing species because successful establishment would not require the simultaneous introduction of two individuals of opposite sexes.
Genomicist Melania Cristescu and her colleagues examined mitochondrial DNA of the fishhook waterflea introduced into the Great Lakes, tracing the source of the invasive populations to the Baltic Sea.
[12] More recently, Cristescu has argued for expanding the use of phylogenetic and phylogenomic approaches, as well as applying metabarcoding and population genomics, to understand how species are introduced and identify "failed invasions" where introduction does not lead to establishment.
[13] Propagule pressure describes the number of individuals introduced into an area in which they are not native, and can strongly affect the ability of species to reach a later stage of invasion.
Factors which may influence the rate of transport and introduction into a novel environment include the species' abundance in its native range, as well as its tendency to co-occur with or be deliberately moved by humans.
Mark van Kleunen, in revisiting the question, proposed examining the traits of candidate invaders in the context of the process of biological invasion.
The evolutionary ecologist Katrina Dlugosch has noted that the relationship between genetic variation and capacity for adaptation is nonlinear and may depend on factors such as the effect size of adaptive loci (in quantitative genetics, effect size refers to the magnitude of change in a phenotypic trait value associated with a particular locus) and the presence of cryptic variation.
Herbert G. Baker proposed that the possession of "general purpose" genotypes which were tolerant of a range of environments could be advantageous for species introduced into new areas.
During a range expansion, there exists an expanding wave front, where rapidly-growing populations are established by a relatively small number of individuals.
[27] The first systematic review of the role of invasive plant species in interspecific hybridization appeared in 1992,[28] and the phenomenon has also been explored in fish and aquatic invertebrates.
The ecologists Jennifer Lau and Casey terHorst have pointed to this absence of an evolutionary response as an important consideration for understanding how invasive species disrupt ecological communities and the multiple challenges faced by native populations.
