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

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?


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)



1. Reproductive system• Dioecious vs. Monoecious• Self-incompatible pollen vs. Self-compatible pollen



1. Reproductive system• Dioecious vs. Monoecious• Self-incompatible pollen vs. Self-compatible pollen• Some type of asexual reproduction

Apomixis – produce viable seed without fertilizationVegetative reproduction – regenerate from stem or root fragmentsClonal propagation – new individuals produced through rhizomes



1. Reproductive system (tend to be: self-compatible monoecious w/ asexual reproduction)

2. Flowering & fruiting periods• Short vs. Long flowering period



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



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




2. Flowering & fruiting periods (tend to be: long)3. Juvenile period (tend to be: short)4. Seed production• Low vs. high




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




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




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




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)


SUMMARY: Is it characteristics of the species or characteristics of the environment?

X


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)


Fundamental niche formalized by Hutchinson in 1957.= theoretical limits of existence for a species along n resource

axes


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


Fundamental niche – Species A

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Fundamental niche – Species A, Species B

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Realized niche – Species A, Species B

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Realized niche – Species A, Species BFundamental niche: Invader – Species C

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Realized niche – Species A, Species BFundamental niche: Invader – Species C

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New realized niche – Species A, Species BRealized niche: Invader – Species C

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Realized niche – Species A, Species BRealized niche: Invader – Species CFundamental niche: Invader – Species D

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Realized niche – Species A, Species BRealized niche: Invader – Species CFundamental niche: Invader – Species D

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New realized niche – Species A, Species BRealized niche: Invader – Species CRealized niche: Invader – Species D

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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


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 communityThus 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)



Expectations:(1) Caucasus grasses do better than Montana grasses when grown

with C. diffusa





with C. diffusa(2) C. diffusa does better when grown with Montana grasses then when

it is grown with Caucasus grasses


Expectations:(1) Caucasus grasses do better

than Montana grasses when grown with C. diffusa

(1)


Expectations:(1) Caucasus grasses do better

than Montana grasses when grown with C. diffusa• Yes (bigger drops with

Montana)

(1)


Expectations:(2) C. diffusa does better when

grown with Montana grasses then when it is grown with Caucasus grasses (2)


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)



native habitat in Caucasus• Grew plants with and without activated charcoal



it is grown with Caucasus grasses(3) Activated charcoal reduces the negative effects on Montana

grasses but has little effect on Caucasus grasses


Expectations:(3) Activated charcoal reduces

the negative effects on Montana grasses but has little effect on Caucasus grasses

(1)

(3)


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

(3)

(1)


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.

(2)

(3)

(1)(3)



native habitat in Caucasus• Grew plants with and without activated charcoal• Measured competition for P



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




• Bais et al. (2003) Science 301:1377-1380Identified the specific allelochemical: (–)-catechin(A) Higher concentration in C. diffusa soils




• Bais et al. (2003) Science 301:1377-1380Identified the specific allelochemical: (–)-catechin(A) Higher concentration in C. diffusa soils(B) Inhibit germination of Montana grasses




• Bais et al. (2003) Science 301:1377-1380Identified the specific allelochemical: (–)-catechin(A) Higher concentration in C. diffusa soils(B) Inhibit germination of Montana grasses(C) Inhibit growth of Montana grasses


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

Documents

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