sept.16- hypotheses continued (variable resource, competition, novel weapons) 18- hypotheses finish!...
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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
rce
supp
ly-up
take
isoc
line
3) What makes a species invasive?
Variable resource availability hypothesis
Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534Background: • 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
Res
ourc
e up
take
Resou
rce
supp
ly-up
take
isoc
line
3) What makes a species invasive?
Variable resource availability hypothesis
Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534Background: • 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
Res
ourc
e up
take
Resou
rce
supp
ly-up
take
isoc
line
Gross resource supply
Res
ourc
e up
take
Resou
rce
supp
ly-up
take
isoc
line
Resist
ant t
o In
vasio
n
Easily
Inva
sible
AB
CD
3) What makes a species invasive?
Variable resource availability hypothesis
Davis et al. (2000) JOURNAL OF ECOLOGY 88 (3): 528-534Background: • 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
Res
ourc
e up
take
Resou
rce
supp
ly-up
take
isoc
line
Gross resource supply
Res
ourc
e up
take
Resou
rce
supp
ly-up
take
isoc
line
Resist
ant t
o In
vasio
n
Easily
Inva
sible
AB
CD
Example:
Lepš et al . 2002. Applied Vegetation
Science
Piper aduncumNative range: Central AmericaInvaded range: Papua New
Guinea
.
3) What makes a species invasive?
Variable resource availability hypothesis
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?
3) What makes a species invasive?
Variable resource availability hypothesis
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
3) What makes a species invasive?
Variable resource availability hypothesis
3) 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.
3) 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!
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 resourcesi.e. better competitors
Realized niche – Species A, Species BFundamental niche: Invader – Species C
Resource axis #1
Res
ourc
e ax
is #
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 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.
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 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.
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 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.
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 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.
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 (esp. @ low light)
↑ shade
Sun
ShadePartial shade
ShadePartial shadeSun
3) What makes a species invasive?Competition hypothesis
Example: Pattison et al. (1998)• Conclusion: the invasive plants were better competitors for
light.
↑ shade
Sun
ShadePartial shade
ShadePartial shadeSun
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 83:7-13Natives 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 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
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 HypothesisBCW = Belowground Chemical Warfare
www.soq.wur.nl
Background• Roots can be very leaky creating a
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’
3) What makes a species invasive?
BCW previously known as Novel Weapons Hypothesis
www.soq.wur.nl
Background• Roots can be very leaky creating a
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
3) What makes a species invasive?
BCW previously known as Novel Weapons Hypothesis
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 + -
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. 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]
3) 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
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)
Self other
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)
Self other
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 careMontana= 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)
Self other
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?