3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events are a central feature of invasive plants

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects = founders of a new population carry only a fraction of the total genetic variation of the source populations

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects = founders of a new population carry only a fraction of the total genetic variation of the source populations Climate matching = different genetic stock succeed in different parts of introduced range; often correspond to similar latitudes or climate in native range. e.g. tamarisk in US.

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks = loss of genetic variation when population size drastically decreases; often associated with catastrophic events that result in mass mortality

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift = loss of genetic variation by chance when populations are small and do not have complete, random interbreeding

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection: strong selective forces often apply to successful colonizers

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment – rapid adaptive responses over short times and within short distances to new environment

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment – rapid adaptive responses over short times and within short distances to new environment e.g.. Bearded Goatgrass in CA: ‘competitive’ VS ‘seed producing’ phenotypes in invasion front VS monoculture.

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment – shifts in relative proportions of competition vs. defense vs. reproductive pressures e.g. Leger 2003.

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity ↓reproductive barriers

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity ↓reproductive barriers Transfers or originates adaptations

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants 2834 plant species in the British Isles Of these, 715 (25%) are hybrids 74 are native X alien 21 are alien X alien 95 (13% of hybrids) involve aliens

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization Interspecific – often with other species in new environment

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization Interspecific Intraspecific – often with populations from native range that would not normally occur

Determining genetic change and hybridization How?

Determining genetic change and hybridization How? Morphology and cytology Genetic analyses – chloroplast, nuclear, ribosomal DNA Experiments (common garden)

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Introgression = back cross with 1 or more parents P 1 X P 2 → F 1 F 1 X {P 1, P 2 } → F 2 introgressant

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Introgression = back cross with 1 or more parents Stabilized = viable, fertile hybrids

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Hybrids form new Intraspecific taxa

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Hybrids form new intraspecific taxa Hybrids form new Species – Note: all examples are alien X alien

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Allopolyploids = hybrid between different species in which chromosomes of both parents are retained

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Allopolyploids Hybrids form new Species – Note: both Tragopogon’s are alien X alien

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Specific Example: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9: Natural distribution: south of Black Sea with disjunct populations in Lebanon, Spain, & Portugal Extensively naturalized throughout British Isles

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Specific Example: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9: Natural distribution: south of Black Sea with disjunct populations in Lebanon, Spain, & Portugal Extensively naturalized throughout British Isles Origin unclear: Earliest known introduction (1763) from Spain But subsequent introductions likely, especially from Black Sea area Also can’t tell from morphological information where it came from, but know from morphology that had to hybridize at some time R. ponticum cultivated along with other introduced species

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Specific Example: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9: Most individuals from naturalized populations had genotypes from Spain (88%), followed by Portugal (10%) No genotypes from Black Sea region

3)What makes a species invasive? f) Micro-evolutionary change hypothesis Specific Example: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9: Most individuals from naturalized populations had genotypes from Spain (88%), followed by Portugal (10%) No genotypes from Black Sea region Small number of individuals had hybridized with at least 3 other species Occurrence of R. catawbiense genotypes most common in Scotland (coldest area of British Isle) Introgression with catawbiense appears to have conferred cold tolerance into ponticum

Another example: Tamarisk in US Gaskin and Shaal PNAS 99 (17): Used DNA sequencing to determine origins and relationships of plants (nuclear gene intron) Little similarity in genetic types between US and Eurasia (4 common of 58 types) Most common species in US invasion was hybrid between 2 Eurasian species (Tamarix chinensis and Tamarix ramosissima) Hybrid unknown in Asia (species geographically isolated)

Evidence for genetic change in invasive species Leger and Rice 2003, Eschultzia californica Used common garden to look for genetic VS phenotypic traits Plants from Chile (invaded range) were larger with no competitors

Leger and Rice Ecology Letters

3)What makes a species invasive? f) Micro-evolutionary change hypothesis SUMMARY: Micro-evolutionary change hypothesis Likely that most (if not all) invasive species go through founder events, experience genetic bottlenecks & drift, and undergo selection In other words micro-evolutionary changes Good evidence for hybridization being beneficial

3)What makes a species invasive? f) Micro-evolutionary change hypothesis SUMMARY: Micro-evolutionary change hypothesis Likely that most (if not all) invasive species go through micro- evolutionary changes Good evidence for hybridization being beneficial But Have evidence of micro-evolutionary changes for only a limited number of species For only a subset of these, have evidence that micro-evolutionary changes have been beneficial A species that undergoes micro- (or even macro-) evolutionary changes does not automatically become invasive

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species are immigrants to a new area Aliens often arrive as seeds

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species are immigrants to a new area Aliens often arrive as seeds In other words, they arrive without the grazers, insect pests, diseases, parasites, etc. of their native range – their “enemies”

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Hence, alien species “escapes” from their enemies and are no longer affected by biotic constraints Thus, alien growth and success is much greater in new range

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists?

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small?

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small? Do potential enemies feed on foliage or seeds?

3)What makes a species invasive? g) Escape from biotic constraints hypothesis aka“Escape from enemy” hypothesis “Enemy release” hypothesis Basic concepts: Species in their native range are suppressed by natural enemies Alien species immigrate without enemies Aliens lack biotic constraints However, alien success will depend on potential enemies in new range: Are potential enemies generalists or specialists? Are population sizes of potential enemies large or small? Do potential enemies feed on foliage or seeds? Are there similar hosts for potential enemies in new area?