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Sept. 16- Hypotheses continued (Variable resource, competition, novel weapons)

Sept. 16- Hypotheses continued (Variable resource, competition, novel weapons) 18- Hypotheses finish! (disturbance, biodiversity, anthropogenic)

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Sept. 16- Hypotheses continued (Variable resource, competition, novel weapons)

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  1. Sept. 16- Hypotheses continued (Variable resource, competition, novel weapons) 18- Hypotheses finish! (disturbance, biodiversity, anthropogenic) 23- Nevada Cooperative Extension outreach programs (Earl Creech) 25- State weed & invasive plants management (Scott Marsh) 30- Federal invasive plants research (Mark Weltz) Oct. 2- Review 7- Exam 1 (Dr. Nowak is back) Notes: Hopefully we can get the last 6 hypotheses done before the guest lectures. If we can, on Oct 2 I’ll bring in old exams and we can review. *** Information presented by the guest lecturers will be on the exam! ***

  2. What makes a species invasive? • Variable resource availability hypothesis • Davis et al. (2000) JOURNAL OF ECOLOGY • Background: • There is a finite amount of plant resources (nutrients, light, water, ‘space’) at a given site in a given time. • In most plant communities at most times, most of the resources are taken up by plants Resource uptake Resource supply-uptake isocline Gross resource supply

  3. What makes a species invasive? • Variable resource availability hypothesis • Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534 • Background: • There is a finite amount of plant resources (nutrients, light, water, ‘space’) at a given site in a given time. • In most plant communities at most times, most of the resources that are available are taken up by the plants • Plant community becomes • susceptible whenever there • is an increase in the amount • of unused resources Resource uptake Resource supply-uptake isocline Gross resource supply

  4. Resource uptake Resource uptake Resource supply-uptake isocline Resource supply-uptake isocline Resistant to Invasion A B D Easily Invasible C Gross resource supply Gross resource supply • What makes a species invasive? • Variable resource availability hypothesis • Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534 • Background: • There is a finite amount of plant resources (nutrients, light, water, ‘space’) at a given site in a given time. • In most plant communities at most times, most of the resources that are available are taken up by the plants • Plant community becomes • susceptible whenever there • is an increase in the amount • of unused resources

  5. Resource uptake Resource uptake Resource supply-uptake isocline Resource supply-uptake isocline Resistant to Invasion A B D Easily Invasible C Gross resource supply Gross resource supply • What makes a species invasive? • Variable resource availability hypothesis • Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534 • Background: • There is a finite amount of plant resources (nutrients, light, water, ‘space’) at a given site in a given time. • In most plant communities at most times, most of the resources that are available are taken up by the plants • Plant community becomes • susceptible whenever there • is an increase in the amount • of unused resources • These changes will occur • naturally over time and • invader has to be able to • access the resources • This is not a static factor- • it will fluctuate over time!

  6. What makes a species invasive? • Variable resource availability hypothesis • Example: • Lepš et al . 2002. Applied Vegetation • Science • Piper aduncum • Native range: Central America • Invaded range: Papua New Guinea • .

  7. What makes a species invasive? • Variable resource availability hypothesis • Example: • Lepš et al 2002. Applied Vegetation Science • Piper aduncum • Native range: Central America • Invaded range: Papua New Guinea • Invasive Piper should only be found where there are fluctuating resources. • Intact primary forests do not experience pronounced resource fluctuation. Where should resources fluctuate?

  8. What makes a species invasive? • Variable resource availability hypothesis • Example: • Lepš et al 2002. Applied Vegetation Science • Piper aduncum • Native range: Central America • Invaded range: Papua New Guinea • Invasive Piper should only be found where there are fluctuating resources. • Intact primary forests do not experience pronounced resource fluctuation. Where should resources fluctuate? River banks, abandoned gardens, landslide

  9. What makes a species invasive? • Variable resource availability hypothesis Example: Adair et al. 2008. Plant Soil Created gradients with increased resources (N and water) and resident plant mortality. Measured effect on cheatgrass.

  10. What makes a species invasive? • Variable resource availability hypothesis Example: Adair et al. 2008. Plant Soil Created two gradients with increased resources and resident plant mortality measured effect on cheatgrass. Resident plant mortality did not increase cheatgrass!

  11. What makes a species invasive? • Variable resource availability hypothesis • SUMMARY:Variable resource availability hypothesis • Resources naturally fluctuate over time. When resource availability is greater than resource uptake, the system is vulnerable to invasion. • Conceptually appealing • Flexibility to accommodate space & time; many different resources • Experimental evidence • But • Low predictive power • Different invaders respond differently to different resources • Have to know where and when availability increases in complex world to predict susceptibility

  12. What makes a species invasive? • 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.

  13. Realized niche –Species A, Species B Fundamental niche: Invader –Species C Resource axis #2 Resource axis #1 • What makes a species invasive? • Competition hypothesis • Basic concept: • Invasives are inherently better at getting resources • i.e. better competitors

  14. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • RCI= relative competition intensity= (Pmono-pmix/pmono). • Measures how much a plant is effected by competition (competition intensity).

  15. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • RCI= relative competition intensity= (Pmono-pmix/pmono). The bigger the RCI, the greater the decrease because of competition.

  16. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • RCI= relative competition intensity= (Pmono-pmix/pmono). • Aliens decrease native plants much more than native plants decrease aliens. The bigger the RCI, the greater the decrease because of competition.

  17. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • Relative yield- Ymix/Ycontrol • Measures the effect of competition

  18. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • Relative yield- Ymix/Ycontrol • Measures the effect of competition The smaller the number the greater the decrease due to competition.

  19. What makes a species invasive? • Competition hypothesis Example: • Vila and Weiner 2004 Oikos. • Used data for 26 alien and 48 native species. • Relative yield- Ymix/Ycontrol • Measures the effect of competition • More natives are more severely reduced by competition than aliens. The smaller the number the greater the decrease due to competition.

  20. What makes a species invasive? • Competition hypothesis Bidens sandwicensis- Hawaiian native • Example: Pattison et al. (1998) • Tropical rainforest in Hawaii • Studied 4 native species & 5 invasive species (included trees, shrubs, & herbs) • Grew in different light environments representative of rainforest (light is a limiting factor in rainforests) • Expectations: Invasives better at utilizing light Bidens pilosa- Hawaiian invasive

  21. What makes a species invasive? • Competition hypothesis • Example: Pattison et al. (1998) • Shade ↓ RGR of all species, BUT invasives had >RGR • Shade ↑leafiness of all species, BUT invasives had > leafiness (esp. @ low light) ↑ shade Sun Partial shade Shade Shade Partial shade Sun

  22. What makes a species invasive? • Competition hypothesis • Example: Pattison et al. (1998) • Conclusion: the invasive plants were better competitors for light. ↑ shade Sun Partial shade Shade Shade Partial shade Sun

  23. What makes a species invasive? • Competition hypothesis • Evidence: Melgoza et al. (1990) Oecologia 83:7-13 • Greater water stress for natives when Bromus is present • Degree of water stress imposed by Bromus in the first year after burn is similar to that 12 years after burn Chrysothamnus viscidiflorus Stipa comata

  24. What makes a species invasive? • Competition hypothesis • Evidence: Melgoza et al. (1990) Oecologia 83:7-13 • Natives have • Greater water stress with invasives • Less biomass production with invasives

  25. What makes a species invasive? • Competition hypothesis Evidence: Melgoza et al. (1990) Oecologia 83:7-13 Invasive plant (cheatgrass) is a better competitor for water which results in reduced native plants.

  26. What makes a species invasive? • Competition hypothesis • SUMMARY:Competition hypothesis • Every plant has its own intrinsic ability to acquire vital resources, invasives are just better at it than natives (big bullies). • Conceptually appealing • Strong evidence for a number of species in many different habitats • (although sometimes invoked without concrete evidence) • But • Hard to generalize (and hence predict) • Critical resource(s) varies with different environments • Species characteristics that make for 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? • Not all invaders fit model; other factors seem to be important for some species

  27. What makes a species invasive?BCW previously known as Novel Weapons HypothesisBCW = Belowground Chemical Warfare Background • Roots can be very leaky creating a rhizosphere. • Rhizosphere- the area of soil right around and influenced by the root. • High in carbon containing compounds many of which can’t be identified. Includes cell lysates, organic acids, sugars and phenols. www.soq.wur.nl

  28. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis Background • Roots can be very leaky creating a rhizosphere. Basic concept Allelopathy when one plant releases chemicals (allelochemicals) that are toxic to another • some of these carbon compounds in the rhizosphere can function as a chemical ‘weapon’ www.soq.wur.nl

  29. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis Background • Roots can be very leaky creating a rhizosphere. Basic concept Allelopathy when one plant releases chemicals (allelochemicals) that are toxic to another • The invader always releases the same chemicals but……. • In its native range-- the neighbors have adapted. • In its new range– the chemicals are ‘novel’ (new to the system) and neighbors haven’t adapted and are susceptible. →So these ‘novel weapons’ can have a BIG effect www.soq.wur.nl

  30. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Allelopathy is just bad for the neighbor • What about other classic interactions? • Ailanthus altissima (tree of heaven), Bromus tectorum (cheatgrass), Centaurea diffusa (knapweed) • 3 criteria • Novel • Desired effect on self • Desired effect on other

  31. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis Example: Ailanthusaltissima aka tree of heaven Native to central China. Introduced as an ornamental in the US as early as the 1840’s Photos: from Fred Hrusa. Calphotos.com

  32. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Lawrence et al. 1991. American Journal of Botany • Grew Lactuca seeds treated with Ailanthus. Measured germination and root length. • Shorter radicle (root) length when treated under Ailanthus treatment • Shorter roots and less germination with increasing [Ailanthus]

  33. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Lawrence et al. 1991. American Journal of Botany • Novel? Natives don’t elicit the same response • ‘Self effect’? None • ‘Other effect’? Negative

  34. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis BCW = Below Ground Chemical Warfare • Allelopathy is just bad for the neighbor • What about other classic interactions? • Ailanthus altissima (tree of heaven),Bromus tectorum (cheatgrass),Centaurea diffusa (knapweed)

  35. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Claus Holzapfel and David Kafkewitz • All bromus species produce Polyphenol oxidase (PPO) which breaks down phenolics (allelochemicals) • Bromus performs better when there are phenolics in the soil!

  36. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Claus Holzapfel and David Kafkewitz • All bromus species produce Polyphenol oxidase (PPO) which breaks down phenolics (allelochemicals) • Bromus performs better when there are phenolics in the soil! • Novel? Genus bromus were the only grasses tested that produced PPO • Self effect? Yes • Other effect? Not tested, but……

  37. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis BCW = Below Ground Chemical Warfare • Allelopathy is just bad for the neighbor • What about other classic interactions? • Ailanthus altissima (tree of heaven), Bromus tectorum (cheatgrass), Centaurea diffusa (knapweed)

  38. (1) • What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Callaway & Aschehoug (2000) Science • Activated carbon sequesters any allelochemicals • Test novelness and effects on others • Caucasus = old neighbors, shouldn’t care • Montana= new neighbors, should be effected • Found a bigger drop in new neighbor biomass and a subsequent increase with added carbon.

  39. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis • Callaway & Aschehoug (2000) Science • Activated carbon sequesters any allelochemicals • To test positive self effect • Centaurea should do better when it’s allelochemicals work (in the no carbon treatments and with new neighbors).

  40. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis BCW = Below Ground Chemical Warfare • Allelopathy is just bad for the neighbor • What about other classic interactions? • Ailanthus altissima (tree of heaven), Bromus tectorum (cheatgrass), Centaurea diffusa (knapweed)

  41. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis SUMMARY:BCW Hypothesis Plants release chemicals below ground that illicit both intra and interspeices reactions. • Excellent support for some species BUT • How many other species? • Challenges measuring allelochemcials • Preconceptions

  42. What makes a species invasive?BCW previously known as Novel Weapons Hypothesis SUMMARY:BCW Hypothesis Plants release chemicals below ground that elicit both intra- and inter- species reactions. • Excellent support for some species BUT • How many other species? • Challenges measuring allelochemcials • Preconceptions Comments or questions?

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