What makes a species invasive? Required readings: Strauss, S., C. Webb, and N. Salamin Exotic taxa less related to native species are more invasive. Proceedings of the National Academy of Science 103: Alpert, P The advantages and disadvantages of being introduced. Biological Invasions 8: Cappuccino, N. and J. T. Arnason Novel chemistry of invasive exotic plants. Biology Letters 2: (Handout) Callaway, R. and E. Aschehoug Invasive plants versus their new and old neighbors: a mechanism for exotic invasion. Science 290:

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

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 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 = 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 = 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 Fundamental niche – Species A Resource axis #1 Success

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A Resource axis #1 Success Resource axis #2 Success

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A, Species B Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A, Species B Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Fundamental niche – Species A, Species B Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Realized niche – Species A, Species B Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Realized niche – Species A, Species B Fundamental niche: Invader – Species C Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Realized niche – Species A, Species B Fundamental niche: Invader – Species C Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis New realized niche – Species A, Species B Realized niche: Invader – Species C Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Realized niche – Species A, Species B Realized niche: Invader – Species C Fundamental niche: Invader – Species D Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis Realized niche – Species A, Species B Realized niche: Invader – Species C Fundamental niche: Invader – Species D Resource axis #1 Resource axis #2

3)What makes a species invasive? a) Vacant Niche Hypothesis New realized niche – Species A, Species B Realized niche: Invader – Species C Realized niche: Invader – Species D Resource axis #1 Resource axis #2

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 ‘Exotic taxa less related to native species are more invasive’. PNAS 103:

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: 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 (3) (1)

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. (2) (3) (1) (3)

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: 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: 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: 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