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
Resource uptake
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
3) What makes a species invasive?
Variable resource availability hypothesis
Resource uptake
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
Gross resource supply
3) What makes a species invasive?
Variable resource availability hypothesis
Resource uptake
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
A
B
D
C
Gross resource supply
3) What makes a species invasive?
Variable resource availability hypothesis
Resource uptake
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
A
access the resources
B
• This is not a static factorit will fluctuate over time!
D
C
Gross resource supply
3) 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
.
3) 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?
3) 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
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 resources
i.e. better competitors
Resource axis #2
Realized niche – Species A, Species B
Fundamental niche: Invader – Species C
Resource axis #1
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
2g
80
native #2
10 g
6g
40
invasive #1 10 g
9g
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
2g
80
native #2
10 g
6g
40
invasive #1 10 g
9g
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
3) 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
3) 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
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
Chrysothamnus viscidiflorus
Stipa comata
3) 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
Cheatgrass competition
400
Aboveground biomass (g)
Chrysothamnus
300
200
100
Stipa
0
o
co
m
pe
tit
i
he
at
g
on
C
N
C
N
o
ra
ss
co
m
pe
tit
he
at
g
io
n
ra
ss
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.
Cheatgrass competition
400
Aboveground biomass (g)
Chrysothamnus
300
200
100
Stipa
0
o
co
m
pe
tit
i
he
at
g
on
C
N
C
N
o
ra
ss
co
m
pe
tit
he
at
g
io
n
ra
ss
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?
BCW previously known as Novel Weapons Hypothesis
BCW = 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
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
–
some of these carbon compounds in the
rhizosphere can function as a chemical
‘weapon’
www.soq.wur.nl
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
www.soq.wur.nl
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
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
Self
other
• What about other classic
interactions?
Allelopathy
(amensalism)
0
-
• Ailanthus altissima (tree of heaven),
Bromus tectorum (cheatgrass),
Centaurea diffusa (knapweed)
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 care
Montana= new neighbors, should be effected
Found a bigger drop in new neighbor biomass and
a subsequent increase with added carbon.
(1)
3) 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).
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
Comments or questions?