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! ***

3)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 Gross resource supply Resource uptake Resource supply-uptake isocline

3)What makes a species invasive? Variable resource availability hypothesis Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 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 Gross resource supply Resource uptake Resource supply-uptake isocline

3)What makes a species invasive? Variable resource availability hypothesis Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 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 Gross resource supply Resource uptake Resource supply-uptake isocline Gross resource supply Resource uptake Resource supply-uptake isocline Resistant to Invasion Easily Invasible A B C D

3)What makes a species invasive? Variable resource availability hypothesis Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 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! Gross resource supply Resource uptake Resource supply-uptake isocline Gross resource supply Resource uptake Resource supply-uptake isocline Resistant to Invasion Easily Invasible A B C D

Example: Lepš et al Applied Vegetation Science Piper aduncum Native range: Central America Invaded range: Papua New Guinea. 3)What makes a species invasive? Variable resource availability hypothesis

Example: Lepš et al 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? 3)What makes a species invasive? Variable resource availability hypothesis

Example: Lepš et al 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 3)What makes a species invasive? Variable resource availability hypothesis

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

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

3)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

3)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.

3)What makes a species invasive? 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

3)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).

3)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). growth in monoculture growth in mixRCI native #110 g2 g 80 native #210 g6 g 40 invasive #110 g9 g10 invasive #210 g11 g-10 The bigger the RCI, the greater the decrease because of competition.

3)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. growth in monoculture growth in mixRCI native #110 g2 g 80 native #210 g6 g 40 invasive #110 g9 g10 invasive #210 g11 g-10 The bigger the RCI, the greater the decrease because of competition.

3)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

3)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 growth in mono growth in mixRY native # native # invasive # invasive # The smaller the number the greater the decrease due to competition.

3)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. growth in mono growth in mixRY native # native # invasive # invasive # The smaller the number the greater the decrease due to competition.

3)What makes a species invasive? Competition hypothesis 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 sandwicensis- Hawaiian native Bidens pilosa- Hawaiian invasive

Example: Pattison et al. (1998) Shade ↓ RGR of all species, BUT invasives had >RGR Shade ↑leafiness of all species, BUT invasives had > leafiness low light) ↑ shade Sun Shade Partial shade Shade Partial shade Sun 3)What makes a species invasive? Competition hypothesis

Example: Pattison et al. (1998) Conclusion: the invasive plants were better competitors for light. ↑ shade Sun Shade Partial shade Shade Partial shade Sun 3)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 3)What makes a species invasive? Competition hypothesis Chrysothamnus viscidiflorus Stipa comata

Evidence: Melgoza et al. (1990) Oecologia 83:7-13 Natives have Greater water stress with invasives Less biomass production with invasives 3)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. 3)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 3)What makes a species invasive? Competition hypothesis

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. 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis BCW = Belowground Chemical Warfare

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’ 3)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 3)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 Selfother Allelopathy (amensalism) 0- Positive feedback (Commensalism) +0 Antagonism +- 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis

Example: Ailanthus altissima 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 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis

Lawrence et al 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 ] 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis

Lawrence et al American Journal of Botany -Novel? Natives don’t elicit the same response -‘Self effect’? None -‘Other effect’? Negative 3)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) Selfother Allelopathy (amensalism) 0- Positive feedback (Commensalism) +0 Antagonism +- 3)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! 3)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…… 3)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) Selfother Allelopathy (amensalism) 0- Positive feedback (Commensalism) +0 Antagonism +- 3)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. 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis (1)

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). 3)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) Selfother Allelopathy (amensalism) 0- Positive feedback (Commensalism) +0 Antagonism +- 3)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 3)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 3)What makes a species invasive? BCW previously known as Novel Weapons Hypothesis Comments or questions?