What makes a species invasive?
Required readings:
Strauss, S., C. Webb, and N. Salamin. 2006. Exotic taxa less related to
native species are more invasive. Proceedings of the National
Academy of Science 103:5841-5845.
Alpert, P. 2006. The advantages and disadvantages of being
introduced. Biological Invasions 8:1523-1534.
Cappuccino, N. and J. T. Arnason. 2006. Novel chemistry of invasive
exotic plants. Biology Letters 2:189-193.
(Handout) Callaway, R. and E. Aschehoug. 2000. Invasive plants
versus their new and old neighbors: a mechanism for exotic
invasion. Science 290:521-523.
3) What makes a species invasive?
Is it characteristics of the species or characteristics of the
environment?
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system
• Dioecious (male & female flowers on separate plants) vs.
Monoecious (on same plant)
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system
• Dioecious vs. Monoecious
• Self-incompatible pollen vs. Self-compatible pollen
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1.
•
•
•
Reproductive system
Dioecious vs. Monoecious
Self-incompatible pollen vs. Self-compatible pollen
Some type of asexual reproduction
Apomixis – produce viable seed without fertilization
Vegetative reproduction – regenerate from stem or root fragments
Clonal propagation – new individuals produced through rhizomes
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible monoecious w/
asexual reproduction)
2. Flowering & fruiting periods
• Short vs. Long flowering period
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible monoecious w/
asexual reproduction)
2. Flowering & fruiting periods
• Short vs. Long flowering period
• Short vs. Long fruiting period
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period
• Short vs. long
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period (tend to be: short)
4. Seed production
• Low vs. high
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period (tend to be: short)
4. Seed production (tend to be: high)
5. Germination cues
• Present vs. Absent
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period (tend to be: short)
4. Seed production (tend to be: high)
5. Germination cues (tend to be: present)
6. Light requirements
• Low vs. High ability to capture and efficiently use
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period (tend to be: short)
4. Seed production (tend to be: high)
5. Germination cues (tend to be: present)
6. Light requirements
• Low vs. High ability to capture and efficiently use
• High phenotypic plasticity for light & other resources
• High competitive ability for light & other resources
3) What makes a species invasive?
Species characteristics: Plant Life History Traits (Chapter 3 of NRC
2002)
1. Reproductive system (tend to be: self-compatible & monoecious w/
asexual reproduction)
2. Flowering & fruiting periods (tend to be: long)
3. Juvenile period (tend to be: short)
4. Seed production (tend to be: high)
5. Germination cues (tend to be: present)
6. Light requirements (tend to be: highly efficient, plastic, &
competitive)
3) What makes a species invasive?
X
SUMMARY: Is it characteristics of the species or characteristics of the
environment?
3) What makes a species invasive?
Australian WRA (Weed Risk Assessment) model (Pheloung et al 1999)
•
•
•
Uses 49 questions based on main attributes and impacts of weeds
Answers are combined into a ‘weediness risk’ score
Questions are based on
• history/biogeography (domestication, climate and distribution,
weediness elsewhere)
• biology/ecology (undesirable traits, type of plant, reproduction,
dispersal, persistence)
History and origin give more information but still aren’t the whole story.
3) What makes a species invasive?
a) Vacant Niche Hypothesis
“Niche” concept first developed by Grannell in 1917. Found that could
differentiate species of thrushes on the basis of a resource (in his
case, microhabitats)
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Fundamental niche formalized by Hutchinson in 1957.
= theoretical limits of existence for a species along n resource
axes
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Fundamental niche formalized by Hutchinson in 1957.
= theoretical limits of existence for a species along n resource
axes
Realized niche = actual limits of existence for a species
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Success
Fundamental niche – Species A
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Success
Success
Fundamental niche – Species A
Resource axis #1
Resource axis #2
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Fundamental niche – Species A
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Fundamental niche – Species A
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Fundamental niche – Species A, Species B
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Fundamental niche – Species A, Species B
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Fundamental niche – Species A, Species B
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Realized niche – Species A, Species B
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Realized niche – Species A, Species B
Fundamental niche: Invader – Species C
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Realized niche – Species A, Species B
Fundamental niche: Invader – Species C
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
New realized niche – Species A, Species B
Realized niche: Invader – Species C
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Realized niche – Species A, Species B
Realized niche: Invader – Species C
Fundamental niche: Invader – Species D
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
Realized niche – Species A, Species B
Realized niche: Invader – Species C
Fundamental niche: Invader – Species D
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
Resource axis #2
New realized niche – Species A, Species B
Realized niche: Invader – Species C
Realized niche: Invader – Species D
Resource axis #1
3) What makes a species invasive?
a) Vacant Niche Hypothesis
SUMMARY: Vacant niches
• May have some utility for tropical oceanic islands
BUT
• Many potential invaders lack pollinators, symbionts, etc.
• Actual demonstration of “vacant” niche is nearly impossible
3) What makes a species invasive?
a) Vacant Niche Hypothesis
But don’t discard it yet!
1. Darwin (1849): ‘novel’ genera should naturalize more easily
2. Natural enemies should shift on to more similar new species more
easily (enemy escape hypothesis)
3. New life forms can be very successful (annual grasses in NV)
So – species DIFFERENT from those in an ecosystem should be more
successful invaders.
Strauss et al. 2006. ‘Exotic taxa less related to native species are more
invasive’. PNAS 103:5841-5845.
3) What makes a species invasive?
b) “Novel Weapons Hypothesis”
Allelopathy = one plant releases chemicals that are toxic to another
3) What makes a species invasive?
b) “Novel Weapons” hypothesis
Allelopathy = one plant releases chemicals that are toxic to another
• In natural environment, invader releases allelochemicals:
But the other members of the plant community have evolved with
the invader
Thus other plants are relatively immune to the allelochemicals
3) What makes a species invasive?
b) “Novel Weapons” hypothesis
Allelopathy = one plant releases chemicals that are toxic to another
• In natural environment, invader releases allelochemicals:
But the other members of the plant community have evolved with
the invader
Thus other plants are relatively immune to the allelochemicals
•
In new invaded environment, invader releases allelochemicals:
Now the allelochemicals are novel to the other members of the
plant community
Thus other plants are susceptible to damage by the
allelochemicals
3) What makes a species invasive?
b) “Novel Weapons” hypothesis– Callaway & Aschehoug (2000)
Science 290:521-523
Experimental design:
• North American invader: Diffuse knapweed (Centaurea diffusa)
• 3 grass species from new C. diffusa habitat in Montana
• 3 grass species of same or closely-related genera from C. diffusa
native habitat in Caucasus
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Experimental design:
• North American invader: Diffuse knapweed (Centaurea diffusa)
• 3 grass species from new C. diffusa habitat in Montana
• 3 grass species of same or closely-related genera from C. diffusa
native habitat in Caucasus
Expectations:
(1) Caucasus grasses do better than Montana grasses when grown
with C. diffusa
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Experimental design:
• North American invader: Diffuse knapweed (Centaurea diffusa)
• 3 grass species from new C. diffusa habitat in Montana
• 3 grass species of same or closely-related genera from C. diffusa
native habitat in Caucasus
Expectations:
(1) Caucasus grasses do better than Montana grasses when grown
with C. diffusa
(2) C. diffusa does better when grown with Montana grasses then when
it is grown with Caucasus grasses
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(1) Caucasus grasses do better
than Montana grasses when
grown with C. diffusa
(1)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(1) Caucasus grasses do better
than Montana grasses when
grown with C. diffusa
• Yes (bigger drops with
Montana)
(1)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(2) C. diffusa does better when
grown with Montana grasses
then when it is grown with
Caucasus grasses
(2)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(2) C. diffusa does better when
grown with Montana grasses
then when it is grown with
Caucasus grasses
• Yes (bigger drops with
Caucasus)
(2)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Experimental design:
• North American invader: Diffuse knapweed (Centaurea diffusa)
• 3 grass species from new C. diffusa habitat in Montana
• 3 grass species of same or closely-related genera from C. diffusa
native habitat in Caucasus
• Grew plants with and without activated charcoal
Expectations:
(1) Caucasus grasses do better than Montana grasses when grown
with C. diffusa
(2) C. diffusa does better when grown with Montana grasses then when
it is grown with Caucasus grasses
(3) Activated charcoal reduces the negative effects on Montana
grasses but has little effect on Caucasus grasses
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(3) Activated charcoal reduces
the negative effects on
Montana grasses but has
little effect on Caucasus
grasses
(1)
(3)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(3) Activated charcoal reduces
the negative effects on
Montana grasses but has
little effect on Caucasus
grasses
• Montana recover as
predicted. Continued
decline for Caucasus
unexpected
(1)
(3)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Expectations:
(3) Activated charcoal
reduces the negative
effects on Montana
grasses but has little
effect on Caucasus
grasses
• Montana recover
as predicted.
Continued decline
for Caucasus
unexpected, but
may be due to
better performance
of C. diffusa.
(3)
(1)
(3)
(2)
3) What makes a species invasive?
b) Allelopathy Hypothesis – Callaway & Aschehoug (2000)
Experimental design:
• North American invader: Diffuse knapweed (Centaurea diffusa)
• 3 grass species from new C. diffusa habitat in Montana
• 3 grass species of same or closely-related genera from C. diffusa
native habitat in Caucasus
• Grew plants with and without activated charcoal
• Measured competition for P
Expectations:
(1) Caucasus grasses do better than Montana grasses when grown
with C. diffusa
(2) C. diffusa does better when grown with Montana grasses then when
it is grown with Caucasus grasses
(3) Activated charcoal reduces the negative effects on Montana
grasses but has little effect on Caucasus grasses
(4) Activated charcoal reduced P uptake by C. diffusa when grown
with Montana grasses, but increased P uptake by C. diffusa
when grown with Caucasus grasses
3) What makes a species invasive?
b) Allelopathy Hypothesis
Allelopathy Hypothesis
• Strong support from Callaway & Aschehoug (2000):
C. diffusa releases chemicals that are NOT toxic to species in
native Caucasus habitat, but chemicals are toxic to species in
new Montana habitat
3) What makes a species invasive?
b) Allelopathy Hypothesis
Allelopathy Hypothesis
• Strong support from Callaway & Aschehoug (2000):
C. diffusa releases chemicals that are NOT toxic to species in
native Caucasus habitat, but chemicals are toxic to species in
new Montana habitat
•
Bais et al. (2003) Science 301:1377-1380
Identified the specific allelochemical: (–)-catechin
(A) Higher concentration in C. diffusa soils
3) What makes a species invasive?
b) Allelopathy Hypothesis
Allelopathy Hypothesis
• Strong support from Callaway & Aschehoug (2000):
C. diffusa releases chemicals that are NOT toxic to species in
native Caucasus habitat, but chemicals are toxic to species in
new Montana habitat
•
Bais et al. (2003) Science 301:1377-1380
Identified the specific allelochemical: (–)-catechin
(A) Higher concentration in C. diffusa soils
(B) Inhibit germination of Montana grasses
3) What makes a species invasive?
b) Allelopathy Hypothesis
Allelopathy Hypothesis
• Strong support from Callaway & Aschehoug (2000):
C. diffusa releases chemicals that are NOT toxic to species in
native Caucasus habitat, but chemicals are toxic to species in
new Montana habitat
•
Bais et al. (2003) Science 301:1377-1380
Identified the specific allelochemical: (–)-catechin
(A) Higher concentration in C. diffusa soils
(B) Inhibit germination of Montana grasses
(C) Inhibit growth of Montana grasses
3) What makes a species invasive?
b) Allelopathy Hypothesis
SUMMARY: Allelopathy Hypothesis
• Excellent support for C. diffusa
BUT
• How many other species?
Evidence for novel secondary chemicals in invasive VS non-invasive
plants: (Cappuccino and Arnason 2006)
Chemicals related to allelopathy and pathogen and herbivore
resistance