What makes a species invasive?
Is it characteristics of the species ?
What makes a species invasive?
Is it characteristics of the species ?
Plant Life History Traits
1. Reproductive system
•
Dioecious (male & female flowers on separate plants) vs.
Monoecious (on same plant)
•
Self-incompatible pollen vs. Self-compatible pollen
What makes a species invasive?
Is it characteristics of the species ?
Plant Life History Traits
1. Reproductive system
•
Dioecious (male & female flowers on separate plants) vs.
Monoecious (on same plant)
•
Self-incompatible pollen vs. Self-compatible pollen
•
Asexual vs. sexual reproduction
Apomixis – produce viable seed without fertilization
Vegetative reproduction – regenerate from stem or root
fragments
Clonal propagation – new individuals produced through
rhizomes
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• tend to be: self-compatible, monoecious, asexual
2.Flowering & fruiting periods
•
•
Short vs. Long flowering period
Short vs. Long fruiting period
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
•
Low vs. High
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
• Tend to be: high
4.Germination cues/dormancy
•
Present vs. Absent
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
• Tend to be: high
4. Germination cues/dormancy
• Tend to be: present
5. Juvenile period
•
Short vs. Long
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
• Tend to be: high
4. Germination cues/dormancy
• Tend to be: present
5. Juvenile period
• Tend to be: short
6. Phenotypic plasticity
What makes a species invasive?
Richards et al. (2006) Ecology Letters 9: 981-993
Phenotypic plasticity: the property of a
genotype to express different phenotypes in
different environments.
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
• Tend to be: high
4. Germination cues/dormancy
• Tend to be: present
5. Juvenile period
• Tend to be: short
6. Phenotypic plasticity
•
High vs. Low
What makes a species invasive?
Plant Life History Traits
1. Reproductive system
• Tend to be: self-compatible, monoecious, asexual
2. Flowering & fruiting periods
• Tend to be: long
3. Seed production
• Tend to be: high
4. Germination cues/dormancy
• Tend to be: present
5. Juvenile period
• Tend to be: short
6. Phenotypic plasticity
• Tend to be: high
7.Competitive ability
•
High vs. Low
What makes a species invasive?
X
SUMMARY: Is it characteristics of the species?
If not simply a characteristic of the species, then is
it a characteristic of the environment?
Are certain environments more invasible?
What makes a species invasive?
Is it characteristics of the
environment?
Environmental Traits
1. Old world vs. New World
What makes a species invasive?
Is it characteristics of the
environment?
Environmental Traits
1. Old world vs. New World
• Tend to be: New world
2. Species rich vs. Species poor
What makes a species invasive?
Is it characteristics of the
environment?
Environmental Traits
1. Old world vs. New World
• Tend to be: New world
2. Species rich vs. Species poor
• Tend to be: species rich
3. Temperate vs. Tropical
What makes a species invasive?
Is it characteristics of the
environment?
Environmental Traits
1. Old world vs. New World
• Tend to be: New world
2. Species rich vs. Species poor
• Tend to be: species poor
3. Temperate vs. Tropical
• Tend to be: Temperate
4. Island vs. Mainland
What makes a species invasive?
Is it characteristics of the
environment?
Environmental Traits
1. Old world vs. New World
• Tend to be: New world
2. Species rich vs. Species poor
• Tend to be: species poor
3. Temperate vs. Tropical
• Tend to be: Temperate
4. Island vs. Mainland
• Tend to be: Islands
5. Natural vs. Artificial
What makes a species invasive?
X
SUMMARY: Is it characteristics of the species?
If not simply a characteristic of the species, then is
it a characteristic of the environment?
X
Or, is it a characteristic of both the species and environment?
10 hypotheses:
Competition hypothesis
Escape from biotic constraints hypothesis
BCW hypothesis
Microevolutionary change hypothesis
Vacant niche hypothesis
Biodiversity hypothesis
Variable resource availability hypothesis
Disturbance and land use hypothesis
Environmental change hypothesis
Anthropogenic hypothesis
Competition Hypothesis
Background:
• Plants require several resources to grow and reproduce
• Plants use different strategies to compete for resources
VS
Philip Grime
David Tilman
Competition Hypothesis
C (competition)
Background:
• Competition Strategies: Grime
K
(ruderal) R
HABITAT
productivity
disturbance
r
S (Stress)
SPECIES
Highly competitive (C)
productivity
Stress-tolerant (S)
disturbance
Ruderal (R)
Competition Hypothesis
Background:
• Competition Strategies: Tilman
Competition Hypothesis
Resource axis #2
Fundamental niche – Species A
Resource axis #1
Competition Hypothesis
Resource axis #2
Fundamental niche – Species A, Species B
Resource axis #1
Competition Hypothesis
Background:
Competition strategies
• How does this apply to invasion?
Invasion is merely a special case of plant succession!
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 resources
i.e. better competitors
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
Competition hypothesis
Evidence:
Vila and Weiner 2004 Oikos 105: 229-238
Conducted a meta-analysis of pair-wise competition studies.
•
RCI (relative competition intensity):Measures how much a
plant is effected by competition (competition intensity).
•
RY (relative yield): Measures the effect of competition
Competition hypothesis
Evidence:
Vila and Weiner 2004 Oikos
105: 229-238
•RCI=(mono-mix/mono).
Non-native plants decrease native plants more
than native plants decrease non-natives.
Competition hypothesis
Evidence:
Vila and Weiner 2004
Oikos.
•RY: Ymix/Ycontrol
More natives are severely reduced by
interspecific competition than non-natives.
Competition hypothesis
Evidence:
Baruch & Goldstein (1999)Oecologia 121: 183-192
•
Broad survey in Hawaii along elevation gradient of tropical
rainforests
•
34 native species
•
30 invasive species
•
Included trees,
shrubs, & herbs
Competition hypothesis
Evidence:
Baruch & Goldstein (1999)
Invasives had
• Bigger leaves
• More
nutrients
• Cost less
to build
• Higher
photosynthesis
• More efficient
N use
Competition hypothesis
Evidence:
Baruch & Goldstein (1999)
Invasives had:
• Bigger leaves
• More nutrients
• Cost less to build
• Higher photosynthesis
• More efficient N use
Overall, invasives are better suited than
natives in capturing and utilizing light in
the light limited tropical rainforest,
especially in high light environments that
characterized disturbed habitats
Competition hypothesis
Evidence:
Melgoza et al. (1990) Oecologia 83:7-13
•Field study of Bromus tectorum competition with 2 native
species, Chrysothamnus viscidiflorus and Stipa comata
•Studied plants in:
(1) Recently-burned area without Bromus
(2) Recently-burned area with Bromus
(3) Old burn (>12 years prior) with Bromus)
Chrysothamnus viscidiflorus
Stipa comata
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.
Competition hypothesis
Evidence:
Melgoza et al. (1990) Oecologia 83:7-13
• Greater water stress
with cheatgrass.
• Less biomass
production with
cheatgrass.
The negative effect of cheatgrass is long-lasting, allowing
it to increase within the post-fire community.
Competition hypothesis
Evidence:
Maron and Marler (2008) J. of Ecology 96: 1187-1197
• Examined competition by 3 different invaders on
established monocultures of 10 native species
Centaurea maculosa
Potentilla recta
Lineria dalmatica
Competition hypothesis
Evidence:
Maron and Marler (2008) J. of Ecology 96: 1187-1197
Watered
Unwatered
• Overall, natives had
no net effect on nonnative biomass.
Competition hypothesis
Evidence:
Maron and Marler (2008)
J. of Ecology 96: 1187-1197
• Non-natives suppressed
native biomass by ~
51%, and water had no
effect.
Overall, non-natives exert
strong competitive dominance
over native species, and this is
unaltered by increased resource
supply.
Unwatered
Watered
Competition hypothesis
Are non-natives always better?
Corbin and D’Antonio (2004) Ecology 85:1273-1283
• Examined productivity in plots composed of:
(1) native perennial bunchgrasses
(2) non-native annual grasses
(3) native perennial + non-native annual grasses
Competition hypothesis
Are non-natives always better?
Corbin and D’Antonio (2004) Ecology 85:1273-1283
• At the start, presence
of non-native annuals
decreased productivity.
• By 3 yr later, there was
no effect of non-native
annuals on native
productivity.
Competition hypothesis
Are non-natives always better?
Corbin and D’Antonio (2004) Ecology 85:1273-1283
• At the start, presence of
native perennials had no
effect on non-native
annual productivity.
• By 3 yr later, there was a
negative effect of native
perennials on non-native
productivity.
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 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?
Readings for Next Class
1.Escape from Biotic Constraints:
Keane, R. Crawley, M. 2002. Exotic plant
invasions and the enemy release hypothesis.
TREE 17:164-170
2.BCW:
Inderjit, Callaway R, Vivanco J (2006) Can plant
biochemistry contribute to understanding of
invasion ecology? TRENDS in Plant Science 11:
574-580