1. What makes a species invasive? Is it characteristics of the species ?

2. What makes a species invasive? Is it characteristics of the species ? Plant Life History Traits 1.Reproductive system Dioecious (male & female flowers on separate plants) vs. Monoecious (on same plant) Self-incompatible pollen vs. Self-compatible pollen

3. What makes a species invasive? Is it characteristics of the species ? Plant Life History Traits 1.Reproductive system Dioecious (male & female flowers on separate plants) vs. Monoecious (on same plant) Self-incompatible pollen vs. Self-compatible pollen Asexual vs. sexual reproduction Apomixis – produce viable seed without fertilization Vegetative reproduction – regenerate from stem or root fragments Clonal propagation – new individuals produced through rhizomes

4. What makes a species invasive? Plant Life History Traits 1.Reproductive system tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Short vs. Long flowering period Short vs. Long fruiting period

5. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3. Seed production Low vs. High

6. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3.Seed production Tend to be: high 4.Germination cues/dormancy Present vs. Absent

7. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3.Seed production Tend to be: high 4.Germination cues/dormancy Tend to be: present 5. Juvenile period Short vs. Long

8. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3.Seed production Tend to be: high 4.Germination cues/dormancy Tend to be: present 5. Juvenile period Tend to be: short 6. Phenotypic plasticity

9. What makes a species invasive? Richards et al. (2006) Ecology Letters 9: 981-993 Phenotypic plasticity : the property of a genotype to express different phenotypes in different environments.

10. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3.Seed production Tend to be: high 4.Germination cues/dormancy Tend to be: present 5. Juvenile period Tend to be: short 6. Phenotypic plasticity High vs. Low

11. What makes a species invasive? Plant Life History Traits 1.Reproductive system Tend to be: self-compatible, monoecious, asexual 2.Flowering & fruiting periods Tend to be: long 3.Seed production Tend to be: high 4.Germination cues/dormancy Tend to be: present 5. Juvenile period Tend to be: short 6. Phenotypic plasticity Tend to be: high 7.Competitive ability High vs. Low

12. What makes a species invasive? SUMMARY: Is it characteristics of the species? X Are certain environments more invasible? If not simply a characteristic of the species, then is it a characteristic of the environment?

13. What makes a species invasive? Is it characteristics of the environment? Environmental Traits 1.Old world vs. New World

14. What makes a species invasive? Is it characteristics of the environment? Environmental Traits 1.Old world vs. New World Tend to be: New world 2.Species rich vs. Species poor

15. What makes a species invasive? Is it characteristics of the environment? Environmental Traits 1.Old world vs. New World Tend to be: New world 2.Species rich vs. Species poor Tend to be: species rich 3.Temperate vs. Tropical

16. What makes a species invasive? Is it characteristics of the environment? Environmental Traits 1.Old world vs. New World Tend to be: New world 2.Species rich vs. Species poor Tend to be: species poor 3.Temperate vs. Tropical Tend to be: Temperate 4.Island vs. Mainland

17. What makes a species invasive? Is it characteristics of the environment? Environmental Traits 1.Old world vs. New World Tend to be: New world 2.Species rich vs. Species poor Tend to be: species poor 3.Temperate vs. Tropical Tend to be: Temperate 4.Island vs. Mainland Tend to be: Islands 5.Natural vs. Artificial

18. What makes a species invasive? SUMMARY: Is it characteristics of the species? X 10 hypotheses: Competition hypothesis Escape from biotic constraints hypothesis BCW hypothesis Microevolutionary change hypothesis Vacant niche hypothesis Biodiversity hypothesis Variable resource availability hypothesis Disturbance and land use hypothesis Environmental change hypothesis Anthropogenic hypothesis Or, is it a characteristic of both the species and environment? If not simply a characteristic of the species, then is it a characteristic of the environment? X

19. Competition Hypothesis Background: Plants require several resources to grow and reproduce Plants use different strategies to compete for resources Philip Grime David Tilman VS

20. Competition Hypothesis Background: Competition Strategies: Grime C (competition) S (Stress)(ruderal) R disturbance productivity r K disturbance HABITATSPECIES Highly competitive (C) productivity Stress-tolerant (S) disturbance Ruderal (R)

21. Background: Competition Strategies: Tilman Competition Hypothesis

22. Fundamental niche – Species A Resource axis #1 Resource axis #2 Competition Hypothesis

23. Fundamental niche – Species A, Species B Resource axis #1 Resource axis #2 Competition Hypothesis

24. Background: Competition strategies How does this apply to invasion? Invasion is merely a special case of plant succession!

25. Competition hypothesis Background: There is a finite amount of plant resources (nutrients, light, water, ‘space’) at a given site in a given time. Every plant has its own abilities to acquire these resources. Basic concept: Invasives are inherently better at getting resources i.e. better competitors

26. Competition hypothesis Basic concept: Invasives are inherently better at getting resources i.e. better competitors Realized niche – Species A, Species B Fundamental niche: Invader – Species C Resource axis #1 Resource axis #2

27. Evidence: Vila and Weiner 2004 Oikos 105: 229-238 Conducted a meta-analysis of pair-wise competition studies. RCI (relative competition intensity):Measures how much a plant is effected by competition (competition intensity). RY (relative yield): Measures the effect of competition Competition hypothesis

28. Evidence: Vila and Weiner 2004 Oikos 105: 229-238 RCI=(mono-mix/mono). Competition hypothesis Non-native plants decrease native plants more than native plants decrease non-natives.

29. Evidence: Vila and Weiner 2004 Oikos. RY: Ymix/Ycontrol More natives are severely reduced by interspecific competition than non-natives. Competition hypothesis

30. Evidence: Baruch & Goldstein (1999)Oecologia 121: 183-192 Broad survey in Hawaii along elevation gradient of tropical rainforests 34 native species 30 invasive species Included trees, shrubs, & herbs Competition hypothesis

31. Evidence: Baruch & Goldstein (1999) Invasives had Bigger leaves Competition hypothesis More nutrients Cost less to build Higher photosynthesis More efficient N use

32. Evidence: Baruch & Goldstein (1999) Invasives had: Bigger leaves More nutrients Cost less to build Higher photosynthesis More efficient N use Competition hypothesis 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

33. Chrysothamnus viscidiflorus Stipa comata Evidence: Melgoza et al. (1990) Oecologia 83:7-13 Field study of 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) Old burn (>12 years prior) with Bromus) Competition hypothesis

34. Evidence: Melgoza et al. (1990) Oecologia 83:7-13 Competition hypothesis Degree of water stress imposed by Bromus in the first year after burn is similar to that 12 years after burn. Greater water stress for natives when Bromus is present.

35. Evidence: Melgoza et al. (1990) Oecologia 83:7-13 Greater water stress with cheatgrass. Competition hypothesis Less biomass production with cheatgrass. The negative effect of cheatgrass is long-lasting, allowing it to increase within the post-fire community.

36. Evidence: Maron and Marler (2008) J. of Ecology 96: 1187-1197 Examined competition by 3 different invaders on established monocultures of 10 native species Competition hypothesis Centaurea maculosaLineria dalmaticaPotentilla recta

37. Competition hypothesis Evidence: Maron and Marler (2008) J. of Ecology 96: 1187-1197 Watered Unwatered Overall, natives had no net effect on non- native biomass.

38. WateredUnwatered Competition hypothesis Evidence: Maron and Marler (2008) J. of Ecology 96: 1187-1197 Non-natives suppressed native biomass by ~ 51%, and water had no effect. Overall, non-natives exert strong competitive dominance over native species, and this is unaltered by increased resource supply.

39. Are non-natives always better? Corbin and D’Antonio (2004) Ecology 85:1273-1283 Examined productivity in plots composed of: (1) native perennial bunchgrasses (2) non-native annual grasses (3) native perennial + non-native annual grasses Competition hypothesis

40. Are non-natives always better? Corbin and D’Antonio (2004) Ecology 85:1273-1283 At the start, presence of non-native annuals decreased productivity. By 3 yr later, there was no effect of non-native annuals on native productivity.

41. Competition hypothesis Are non-natives always better? Corbin and D’Antonio (2004) Ecology 85:1273-1283 At the start, presence of native perennials had no effect on non-native annual productivity. By 3 yr later, there was a negative effect of native perennials on non-native productivity.

42. Every plant has its own intrinsic ability to acquire vital resources, invasives are just better at it than natives (big bullies). Competition hypothesis BUT Hard to generalize (and hence predict) Critical resource(s) varies with different environments Species characteristics that make better competitor varies with type of resource Even for any 1 resource, various ways to be a better competitor Why hasn’t evolution already come up with the strategy in situ? Conceptually appealing Strong evidence for a number of species in many different habitats (although sometimes invoked without concrete evidence)

43. Readings for Next Class 1.Escape from Biotic Constraints: Keane, R. Crawley, M. 2002. Exotic plant invasions and the enemy release hypothesis. TREE 17:164-170 2.BCW: Inderjit, Callaway R, Vivanco J (2006) Can plant biochemistry contribute to understanding of invasion ecology? TRENDS in Plant Science 11: 574-580