Sept.16- Hypotheses continued (Variable resource, competition, novel weapons) 18- Hypotheses finish! (disturbance, biodiversity, anthropogenic) 23- Nevada

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- Review7- 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 ECOLOGYBackground: • 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

Res

ourc

e up

take

Resou

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Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534Background: • There is a finite amount of plant resources (nutrients, light,


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


Res

ourc

e up

take

Resou

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supp

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Res

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Resou

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Res

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take

Resou

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Resist

ant t

o In

vasio

n

Easily

Inva

sible

AB

CD







• 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!


Res

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e up

take

Resou

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Res

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Resou

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supp

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Resist

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Easily

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sible

AB

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Example:

Lepš et al . 2002. Applied Vegetation

Science

Piper aduncumNative range: Central AmericaInvaded range: Papua New

Guinea

.



Example:

Lepš et al 2002. Applied Vegetation Science

Piper aduncumNative range: Central AmericaInvaded 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?



Example:

Lepš et al 2002. Applied Vegetation Science

Piper aduncumNative range: Central AmericaInvaded 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





Example: Adair et al. 2008. Plant Soil

Created gradients with increased resources (N and water) and resident plant mortality. Measured effect on cheatgrass.



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!



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.


Basic concept:• Invasives are inherently

better at getting resourcesi.e. better competitors

Realized niche – Species A, Species BFundamental niche: Invader – Species C

Resource axis #1

Res

ourc

e ax

is #

2


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).


Example:




growth in monoculture

growth in mix RCI

native #1 10 g 2 g 80

native #2 10 g 6 g 40

invasive #1 10 g 9 g 10

invasive #2 10 g 11 g -10

The bigger the RCI, the greater the decrease because of competition.


Example:




•Aliens decrease native plants much more than native plants decrease aliens.

growth in monoculture

growth in mix RCI

native #1 10 g 2 g 80

native #2 10 g 6 g 40

invasive #1 10 g 9 g 10

invasive #2 10 g 11 g -10

The bigger the RCI, the greater the decrease because of competition.


Example:



•Relative yield- Ymix/Ycontrol

•Measures the effect of competition


Example:





growth in mono

growth in mix RY

native #1 10 4 0.4

native #2 10 6 0.6

invasive #1 10 9 0.9

invasive #2 10 11 1.1

The smaller the number the greater the decrease due to competition.


Example:





•More natives are more severely reduced by competition than aliens.

growth in mono

growth in mix RY

native #1 10 4 0.4

native #2 10 6 0.6

invasive #1 10 9 0.9

invasive #2 10 11 1.1

The smaller the number the greater the decrease due to competition.


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 (esp. @ low light)

↑ shade

Sun

ShadePartial shade

ShadePartial shadeSun


Example: Pattison et al. (1998)• Conclusion: the invasive plants were better competitors for

light.

↑ shade

Sun

ShadePartial shade

ShadePartial shadeSun


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

Evidence: Melgoza et al. (1990) Oecologia 83:7-13Natives have• Greater water stress with invasives• Less biomass production with invasives


Evidence: Melgoza et al. (1990) Oecologia 83:7-13

Invasive plant (cheatgrass) is a better competitor for water which results in reduced native plants.


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 environmentsSpecies characteristics that make for better competitor

varies with type of resourceEven 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


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.


BCW previously known as Novel Weapons HypothesisBCW = Belowground Chemical Warfare

www.soq.wur.nl


rhizosphere.

Basic conceptAllelopathy 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’


BCW previously known as Novel Weapons Hypothesis

www.soq.wur.nl


rhizosphere.

Basic conceptAllelopathy 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

• 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

Self other

Allelopathy (amensalism)

0 -

Positive feedback

(Commensalism)+ 0

Antagonism + -



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



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]



Lawrence et al. 1991. American Journal of Botany

-Novel? Natives don’t elicit the same response

-‘Self effect’? None

-‘Other effect’? Negative



BCW = Below Ground Chemical Warfare




Self other


0 -

Positive feedback

(Commensalism)+ 0

Antagonism + -



• 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!



• 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……







Self other


0 -

Positive feedback

(Commensalism)+ 0

Antagonism + -



Callaway & Aschehoug (2000) Science

• Activated carbon sequesters any allelochemicals

Test novelness and effects on others

Caucasus = old neighbors, shouldn’t careMontana= new neighbors, should be effected

Found a bigger drop in new neighbor biomass and a subsequent increase with added carbon.



(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).







Self other


0 -

Positive feedback

(Commensalism)+ 0

Antagonism + -



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



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?

Documents

Sept.16- Hypotheses continued (Variable resource, competition, novel weapons) 18- Hypotheses finish! (disturbance, biodiversity, anthropogenic) 23- Nevada