• Handouts on table near entrance
• Readings:
Melbourne et al (2007) ECOLOGY
LETTERS 10 (1): 77-94
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534
Basic concepts:
• In most plant communities at most times, most of the
resources that are available are taken up by the plants
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is
an increase in the amount of unused resources
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is
an increase in the amount of unused resources
A
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is
an increase in the amount of unused resources
A
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is an
increase in the amount of unused resources
↑ availability (A→B)
A
Gross resource supply
B
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is an
increase in the amount of unused resources
↑ availability (A→B)
↓ uptake (A→C)
A
C
Gross resource supply
B
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is an
increase in the amount of unused resources
↑ availability (A→B)
↓ uptake (A→C)
Both (A→D)
A
B
D
C
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is an
increase in the amount of unused resources
↑ availability (A→B)
↓ uptake (A→C)
Both (A→D)
• Changes in availability
& uptake naturally
occur through time
A
B
D
C
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Resource uptake
Davis et al. (2000)
Basic concepts:
• In most plant communities at most times, most of the resources that
are available are taken up by the plants
• Plant community becomes more susceptible whenever there is an
increase in the amount of unused resources
↑ availability (A→B)
↓ uptake (A→C)
Both (A→D)
• Changes in availability
& uptake naturally
occur through time
• Assumes invaders have
A
B
access to resources
D
C
Gross resource supply
3) What makes a species invasive?
d) Variable resource availability hypothesis
Davis et al. (2000)
Evidence:
• Conducted experiment in relatively unproductive grassland
• Imposed 2 resource gradients
3) What makes a species invasive?
d) Variable resource availability hypothesis
Davis et al. (2000)
Evidence:
• Conducted experiment in relatively unproductive grassland
• Imposed 2 resource gradients
(1) Disturbance gradient to ↓ uptake
Low disturbance
(High uptake)
High disturbance
(Low uptake)
3) What makes a species invasive?
d) Variable resource availability hypothesis
Davis et al. (2000)
Evidence:
• Conducted experiment in relatively unproductive grassland
• Imposed 2 resource gradients
(1) Disturbance gradient to ↓ uptake
(2) Fertility gradient to ↑ supply
High supply
Low supply
High uptake
Low uptake
3) What makes a species invasive?
d) Variable resource availability hypothesis
Davis et al. (2000)
Evidence:
• Conducted experiment in relatively unproductive grassland
• Imposed 2 resource gradients
(1) Disturbance gradient to ↓ uptake
(2) Fertility gradient to ↑ supply
• Seeded 54 alien species
• Measured cover of aliens
High supply
Low cover
of aliens
Low supply
High uptake
Low uptake
3) What makes a species invasive?
d) Variable resource availability hypothesis
Davis et al. (2000)
Evidence:
• Conducted experiment in relatively unproductive grassland
• Imposed 2 resource gradients
(1) Disturbance gradient to ↓ uptake
(2) Fertility gradient to ↑ supply
• Seeded 54 alien species
• Measured cover of aliens
High cover
of aliens
High supply
Low cover
of aliens
Low supply
High uptake
Low uptake
3) What makes a species invasive?
d) Variable resource availability hypothesis
SUMMARY: Variable resource availability hypothesis
• Conceptual appealing
• Flexibility to accommodate space & time; many different resources
• Experimental evidence
3) What makes a species invasive?
d) Variable resource availability hypothesis
SUMMARY: Variable resource availability hypothesis
• Conceptual appealing
• Flexibility to accommodate space & time; many different resources
• Experimental evidence
But
• Low predictive power
Different invaders respond differently to different resources
Have to know where and when availability increases in complex
world to predict susceptibility
3) What makes a species invasive?
d) Variable resource availability hypothesis
SUMMARY: Variable resource availability hypothesis
• Conceptual appealing
• Flexibility to accommodate space & time; many different resources
• Experimental evidence
But
• Low predictive power
Different invaders respond differently to different resources
Have to know where and when availability increases in complex
world to predict susceptibility
• Many invaders don’t fit model
Doesn’t appear to be any changes in resource availability
Other factors (e.g. allelopathy) seem to be more important
3) What makes a species invasive?
e) Competition hypothesis
Basic concept:
• Invasives are inherently better at getting resources
i.e. better competitors
3) What makes a species invasive?
e) Competition hypothesis
Basic concept:
• Invasives are inherently better at getting resources
i.e. better competitors
Resource axis #2
Realized niche – Species A, Species B
Fundamental niche: Invader – Species C
Resource axis #1
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Tropical rainforest in Hawaii
• Studied 4 native species & 5 invasive species
Included trees, shrubs, & herbs
Included a pair congeners (Bidens sandwicensis native & B. pilosa
alien)
• Grew in different light environments representative of rainforest
Light is a limiting factor in rainforests
• Expectations: Invasives better at utilizing light
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• What happens with ↑ shade?
“Relative growth rate” (RGR) = how fast plants grow
“Leaf area ratio” = how leafy plants are
↑ shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR
↑ shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species
↑ shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
↑ shade
Sun
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
↑ shade
Sun
Partial shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR (esp. @
higher light)
↑ shade
Sun
Partial shade
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species
↑ shade
Sun
Partial shade
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
(esp. @ low light)
↑ shade
Sun
Partial shade
Shade
Shade
Partial shade
Sun
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
“Light compensation point” = lowest light with + photosynthesis
“Apparent quantum yield” = how efficiently plants turn light into
chemical energy for photosynthesis
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Higher light compensation point for natives
Sun
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Higher light compensation point for natives, OR invasives
tolerate greater shade
Sun
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasive greater quantum yield
Sun
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasive greater quantum yield, OR invasives more light
efficient
Sun
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
“CO2 assimilation” = photosynthesis
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Sun
Partial shade
Shade
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
• Broad survey in Hawaii along elevation gradient of tropical
rainforests
• 34 native species
• 30 invasives species
• Included trees, shrubs, & herbs
• Included 83 populations (i.e. >1 population for some species)
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
• More nutrients
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
• More nutrients
•
Cost less to build
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
• More nutrients
•
•
Cost less to build
Higher photosynthesis
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
• More nutrients
•
•
Cost less to build
Higher photosynthesis
•
More efficient N use
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Pattison et al. (1998)
• Shade ↓ RGR of all species, BUT invasives had >RGR
• Shade ↑leafiness of all species, BUT invasives had > leafiness
• Leaf photosynthesis:
Invasives tolerate greater shade
Invasives more light efficient
Invasives have greater photosynthetic rates
Evidence: Baruch & Goldstein (1999) Invasives had
• Bigger leaves
• More nutrients
• Cost less to build
• Higher photosynthesis
• More efficient N use
Overall, invasives are better suited than natives in capturing and
utilizing light in the light limited tropical rainforest, especially
in high light environments that characterized disturbed
habitats
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Melgoza et al. (1990) Oecologia 83:7-13
• Field study of invasive annual grass Bromus tectorum competition
with 2 native species Chrysothamnus viscidiflorus and Stipa comata
• Studied plants in
(1) recently-burned area without Bromus
(2) recently-burned area with Bromus
(3) area that had burned >12 years prior (also had Bromus)
• Examined competition for soil water
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Melgoza et al. (1990) Oecologia 83:7-13
• Greater water stress for natives when Bromus is present
• Degree of water stress imposed by Bromus in the first year after
burn is similar to that 12 years after burn
3) What makes a species invasive?
e) Competition hypothesis
Evidence: Melgoza et al. (1990) Oecologia 83:7-13
Natives have
• Greater water stress with invasives
• Less biomass production with invasives
Cheatgrass competition
400
Aboveground biomass (g)
Chrysothamnus
300
200
100
Stipa
0
o
co
m
pe
tit
i
he
at
g
on
C
N
C
N
o
ra
ss
co
m
pe
tit
he
at
g
io
n
ra
ss
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Worked with 2 invasive species in Hawaii in seasonally dry
woodlands:
Schizachyrium condensatum – native to mainland US
Melinis minutiflora – native to Africa
• Both C4 bunchgrasses
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Worked with 2 invasive species in Hawaii in seasonally dry
woodlands:
Schizachyrium condensatum – native to mainland US
Melinis minutiflora – native to Africa
• Both C4 bunchgrasses
• Observed that Melinis appears to replace Schizachyrium
3) What makes a species invasive?
e) Competition hypothesis
increases
declines
Evidence: D’Antonio et al. (2001)
• Worked with 2 invasive species in Hawaii in seasonally dry
woodlands:
Schizachyrium condensatum – native to mainland US
Melinis minutiflora – native to Africa
• Both C4 bunchgrasses
• Observed that Melinis appears to replace Schizachyrium
3) What makes a species invasive?
e) Competition hypothesis
increases
declines
Evidence: D’Antonio et al. (2001)
• Worked with 2 invasive species in Hawaii in seasonally dry
woodlands:
Schizachyrium condensatum – native to mainland US
Melinis minutiflora – native to Africa
• Both C4 bunchgrasses
• Observed that Melinis appears to replace Schizachyrium
3) What makes a species invasive?
e) Competition hypothesis
declines
dec
increases
Evidence: D’Antonio et al. (2001)
• Worked with 2 invasive species in Hawaii in seasonally dry
woodlands:
Schizachyrium condensatum – native to mainland US
Melinis minutiflora – native to Africa
• Both C4 bunchgrasses
• Observed that Melinis appears to replace Schizachyrium
inc
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
Melinis seed is present in unburned areas without adult plants at
densities similar to that of Schizachyrium
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Field experiment where removed Melinis plants from around
Schizachyrium
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Field experiment: removed Melinis plants
Measured change in number of tillers for Schizachyrium through
time
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Field experiment : removed Melinis plants
Measured change in tillers for Schizachyrium
Melinis competition
low
high
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Field experiment : removed Melinis plants
Measured change in tillers for Schizachyrium
After 5 months: when ↓ Melinis competition, ↑ Schizachyrium
Melinis competition
low
high
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Field experiment : removed Melinis plants
Measured change in tillers for Schizachyrium
After 5 months: when ↓ Melinis competition, ↑ Schizachyrium
Trend continues through at least 14 months
Melinis competition
low
high
3) What makes a species invasive?
e) Competition hypothesis
Evidence: D’Antonio et al. (2001)
• Seed banks NOT involved
• Competition involved
Additional field & glasshouse studies indicate Melinis is the better
competitor for both light and N
Dominance of Schizachyrium in unburned areas is simply because
it appeared to get there first!
3) What makes a species invasive?
e) Competition hypothesis
SUMMARY: Competition hypothesis
• Conceptually appealing
• Strong evidence for a number of species in many different habitats
(although sometimes invoked without concrete evidence)
3) What makes a species invasive?
e) Competition hypothesis
SUMMARY: Competition hypothesis
• Conceptually appealing
• Strong evidence for a number of species in many different habitats
(although sometimes invoked without concrete evidence)
But
• Hard to generalize (and hence predict)
Critical resource(s) varies with different environments
Species characteristics that make for better competitor varies with
type of resource
Even for any 1 resource, various ways to be a better competitor
• Why hasn’t evolution already come up with the strategy in situ?
• Not all invaders fit model; other factors seem to be important for
some species
3) What makes a species invasive?
f) Micro-evolutionary change hypothesis
Reading: Leger and Rice (2003) Ecology Letters 6:257-264
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
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
New biotic environment – shifts in relative proportions of
competition vs. defense pressures
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
3) What makes a species invasive?
f) Micro-evolutionary change hypothesis
Hybridization Evidence:
• Stabilized introgressants
Introgression = back cross with 1 or more parents
P1 X P2 → F1
F1 X {P1, P2} → F2 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 9:541-556
• 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 9:541-556
• 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 9:541-556
• 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 9:541-556
• 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
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 microevolutionary 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