Handouts on table near entrance

1

• Handouts on table near entrance

2

• Readings
• Melbourne et al (2007) ECOLOGY LETTERS 10 (1)
  77-94

3

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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

Resource uptake
Resource supply-uptake isocline
Gross resource supply
4

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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

Resource uptake
Resource supply-uptake isocline
Gross resource supply
5

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
Gross resource supply
6

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
Easily Invasible
Gross resource supply
7

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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)

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
B
Easily Invasible
Gross resource supply
8

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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)

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
B
Easily Invasible
C
Gross resource supply
9

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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)

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
B
D
Easily Invasible
C
Gross resource supply
10

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
B
D
Easily Invasible
C
Gross resource supply
11

• What makes a species invasive?
• d) Variable resource availability hypothesis

• 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
• access to resources

Resource uptake
Resource supply-uptake isocline
Resistant to Invasion
A
B
D
Easily Invasible
C
Gross resource supply
12

• 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

13

• 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

High disturbance (Low uptake)
Low disturbance (High uptake)
14

• 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
Low uptake
High uptake
15

• 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
Low uptake
High uptake
16

• 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
Low uptake
High uptake
17

• 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

18

• 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

19

• 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 dont fit model
• Doesnt appear to be any changes in resource
  availability
• Other factors (e.g. allelopathy) seem to be more
  important

20

• What makes a species invasive?
• e) Competition hypothesis

• Basic concept
• Invasives are inherently better at getting
  resources
• i.e. better competitors

21

• What makes a species invasive?
• e) Competition hypothesis

• Basic concept
• Invasives are inherently better at getting
  resources
• i.e. better competitors

22

• 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

23

• 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
24

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR

? shade
25

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species

? shade
26

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had gtRGR

? shade
Sun
27

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had gtRGR

? shade
Sun
Partial shade
28

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR (esp. _at_ higher light)

? shade
Sun
Partial shade
Shade
29

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species

? shade
Sun
Partial shade
Shade
30

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness (esp. _at_ low light)

? shade
Sun
Partial shade
Shade
Shade
Partial shade
Sun
31

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis

32

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Light compensation point lowest light with
  photosynthesis
• Apparent quantum yield how efficiently plants
  turn light into chemical energy for photosynthesis

33

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Higher light compensation point for natives

Sun
Shade
34

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Higher light compensation point for natives, OR
  invasives tolerate greater shade

Sun
Shade
35

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Invasives tolerate greater shade
• Invasive greater quantum yield

Sun
Shade
36

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Invasives tolerate greater shade
• Invasive greater quantum yield, OR invasives more
  light efficient

Sun
Shade
37

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Invasives tolerate greater shade
• Invasives more light efficient
• CO2 assimilation photosynthesis

38

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Invasives tolerate greater shade
• Invasives more light efficient
• Invasives have greater photosynthetic rates

Sun
Partial shade
Shade
39

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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. gt1 population for
  some species)

40

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt leafiness
• Leaf photosynthesis
• Invasives tolerate greater shade
• Invasives more light efficient
• Invasives have greater photosynthetic rates
• Evidence Baruch Goldstein (1999)
• Invasives had
• Bigger leaves

41

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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

42

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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

43

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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

44

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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

45

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Pattison et al. (1998)
• Shade ? RGR of all species, BUT invasives had
  gtRGR
• Shade ?leafiness of all species, BUT invasives
  had gt 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

46

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Melgoza et al. (1990) Oecologia 837-13
• 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 gt12 years prior (also
  had Bromus)
• Examined competition for soil water

47

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Melgoza et al. (1990) Oecologia 837-13
• 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

48

• What makes a species invasive?
• e) Competition hypothesis

• Evidence Melgoza et al. (1990) Oecologia 837-13
• Natives have
• Greater water stress with invasives
• Less biomass production with invasives

49

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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

50

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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

51

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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

increases
declines
52

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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

increases
declines
53

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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

dec
inc
increases
declines
54

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio et al. (2001)
• Seed banks NOT involved
• Melinis seed is present in unburned areas without
  adult plants at densities similar to that of
  Schizachyrium

55

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio et al. (2001)
• Seed banks NOT involved
• Competition involved
• Field experiment where removed Melinis plants
  from around Schizachyrium

56

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio et al. (2001)
• Seed banks NOT involved
• Competition involved
• Field experiment removed Melinis plants
• Measured change in number of tillers for
  Schizachyrium through time

57

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio et al. (2001)
• Seed banks NOT involved
• Competition involved
• Field experiment removed Melinis plants
• Measured change in tillers for Schizachyrium

Melinis competition
low
high
58

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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
59

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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
60

• What makes a species invasive?
• e) Competition hypothesis

• Evidence DAntonio 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!

61

• 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)

62

• 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 hasnt evolution already come up with the
  strategy in situ?
• Not all invaders fit model other factors seem to
  be important for some species

63

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis
• Reading Leger and Rice (2003) Ecology Letters
  6257-264

• Micro-evolutionary change hypothesis
• Frequent colonizing events are a central feature
  of invasive plants

64

• 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

65

• 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

66

• 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

67

• 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

68

• 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

69

• 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

70

• 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

71

• 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

72

• 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

73

• 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

74

• 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

75

• 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

76

• 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

77

• 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

78

• 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

79

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Hybridization Evidence
• Stabilized introgressants
• Hybrids form new Intraspecific taxa

80

• 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

81

• 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

82

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Hybridization Evidence
• Stabilized introgressants
• Allopolyploids
• Hybrids form new Species Note both
  Tragopogons are alien X alien

83

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Specific Example Rhododendron ponticum in
  British Isles
• Milne Abbott (2000) Molecular Ecology
  9541-556
• Natural distribution south of Black Sea with
  disjunct populations in Lebanon, Spain,
  Portugal
• Extensively naturalized throughout British Isles

84

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Specific Example Rhododendron ponticum in
  British Isles
• Milne Abbott (2000) Molecular Ecology
  9541-556
• 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 cant 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

85

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Specific Example Rhododendron ponticum in
  British Isles
• Milne Abbott (2000) Molecular Ecology
  9541-556
• Most individuals from naturalized populations had
  genotypes from Spain (88), followed by Portugal
  (10)
• No genotypes from Black Sea region

86

• What makes a species invasive?
• f) Micro-evolutionary change hypothesis

• Specific Example Rhododendron ponticum in
  British Isles
• Milne Abbott (2000) Molecular Ecology
  9541-556
• 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

87

• 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

88

• 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