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What makes a species 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.

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What makes a species invasive?

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  1. 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.

  2. 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) • Reproductive system • Dioecious (male & female flowers on separate plants) vs. Monoecious (on same plant)

  4. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system • Dioecious vs. Monoecious • Self-incompatible pollen vs. Self-compatible pollen

  5. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • 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

  6. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible monoecious w/ asexual reproduction) • Flowering & fruiting periods • Short vs. Long flowering period

  7. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible monoecious w/ asexual reproduction) • Flowering & fruiting periods • Short vs. Long flowering period • Short vs. Long fruiting period

  8. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period • Short vs. long

  9. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period (tend to be: short) • Seed production • Low vs. high

  10. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period (tend to be: short) • Seed production (tend to be: high) • Germination cues • Present vs. Absent

  11. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period (tend to be: short) • Seed production (tend to be: high) • Germination cues (tend to be: present) • Light requirements • Low vs. High ability to capture and efficiently use

  12. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period (tend to be: short) • Seed production (tend to be: high) • Germination cues (tend to be: present) • 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

  13. What makes a species invasive? • Species characteristics: Plant Life History Traits (Chapter 3 of NRC 2002) • Reproductive system (tend to be: self-compatible & monoecious w/ asexual reproduction) • Flowering & fruiting periods (tend to be: long) • Juvenile period (tend to be: short) • Seed production (tend to be: high) • Germination cues (tend to be: present) • Light requirements (tend to be: highly efficient, plastic, & competitive)

  14. What makes a species invasive? X SUMMARY: Is it characteristics of the species or characteristics of the environment?

  15. 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.

  16. 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)

  17. 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

  18. 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

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

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

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

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

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

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

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

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

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

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

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

  30. 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 #2 Resource axis #1

  31. 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 #2 Resource axis #1

  32. 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 #2 Resource axis #1

  33. 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

  34. 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.

  35. What makes a species invasive? • b) “Novel Weapons Hypothesis” Allelopathy = one plant releases chemicals that are toxic to another

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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)

  42. What makes a species invasive? • b) Allelopathy Hypothesis – Callaway & Aschehoug (2000) • Expectations: • Caucasus grasses do better than Montana grasses when grown with C. diffusa • Yes (bigger drops with Montana) (1)

  43. 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)

  44. 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)

  45. 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

  46. 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)

  47. 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)

  48. 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)

  49. 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

  50. 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

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