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 Traits1. Reproductive system

• Dioecious (male & female flowers on separate plants) vs. Monoecious (on same plant)

• Self-incompatible pollen vs. Self-compatible pollen




• Dioecious (male & female flowers on separate plants) vs. Monoecious (on same plant)

• Self-incompatible pollen vs. Self-compatible pollen

• Asexual vs. sexual reproductionA

pomixis – produce viable seed without fertilization

Vegetative reproduction – regenerate from stem or root

fragments

Clonal propagation – new individuals produced through

rhizomes



• tend to be: self-compatible, monoecious, asexual2.Flowering & fruiting periods

• Short vs. Long flowering period• Short vs. Long fruiting period



• Tend to be: self-compatible, monoecious, asexual2. Flowering & fruiting periods

• Tend to be: long3. Seed production

• Low vs. High





• Tend to be: high4.Germination cues/dormancy

• Present vs. Absent





• Tend to be: high4. Germination cues/dormancy

• Tend to be: present5. Juvenile period

• Short vs. Long







• Tend to be: short• Phenotypic plasticity


Richards et al. (2006) Ecology Letters 9: 981-993

Phenotypic plasticity: the property of a genotype to express different phenotypes in different environments.








• High vs. Low

What makes a species invasive?Plant Life History Traits1. Reproductive system






• Tend to be: high• Competitive ability

• High vs. Low


SUMMARY: Is it characteristics of the species?X

Are certain environments more invasible?

If not simply a characteristic of the species, then is it a characteristic of the environment?


Is it characteristics of the environment?

Environmental Traits1. Old world vs. New World




• Tend to be: New world2. Species rich vs. Species poor





• Tend to be: species rich3. Temperate vs. Tropical





• Tend to be: species poor3. Temperate vs. Tropical

• Tend to be: Temperate4. Island vs. Mainland





• Tend to be: species poor3. Temperate vs. Tropical

• Tend to be: Temperate4. Island vs. Mainland

• Tend to be: Islands• Natural vs. Artificial


SUMMARY: Is it characteristics of the species?X

10 hypotheses:Competition hypothesisEscape from biotic constraints hypothesisBCW hypothesisMicroevolutionary change hypothesisVacant niche hypothesisBiodiversity hypothesisVariable resource availability hypothesisDisturbance and land use hypothesisEnvironmental change hypothesisAnthropogenic hypothesis

Or, is it a characteristic of both the species and environment?

If not simply a characteristic of the species, then is it a characteristic of the environment?X

Competition Hypothesis

Background:• Plants require several resources to grow and reproduce• Plants use different strategies to compete for resources

Philip Grime David Tilman

VS


Background:• Competition Strategies: Grime

C (competition)

S (Stress)(ruderal) R

dist

urba

nce

productivity

r

K

productivity disturbance

HABITAT SPECIES

Highly competitive (C)

productivity Stress-tolerant (S)

disturbance Ruderal (R)

Background:• Competition Strategies: Tilman


Fundamental niche – Species A

Resource axis #1

Reso

urce

axi

s #2


Fundamental niche – Species A, Species B

Resource axis #1

Reso

urce

axi

s #2



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 resourcesi

.e. better competitors


Basic concept:• Invasives are inherently better at getting resources

i.e. better competitors

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

Resource axis #1

Reso

urc

e a

xis

#2

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


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.

Evidence:

Vila and Weiner 2004 Oikos.

•RY: Ymix/Ycontrol

More natives are severely reduced by interspecific competition than non-natives.


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


Evidence: Baruch & Goldstein (1999)Invasives had• Bigger leaves


• More nutrients

• Cost less to build

• Higher photosynthesis

• More efficient N use

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

Chrysothamnus viscidiflorus Stipa comata

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)




• Degree of water stress imposed by Bromus in the first year after burn is similar to that 12 years after burn.

• Greater water stress for natives when Bromus is present.


• 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.

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 Lineria dalmaticaPotentilla recta

Competition hypothesis Evidence:Maron and Marler (2008) J. of Ecology 96: 1187-1197

Watered

Unwatered

• Overall, natives had no net effect on non-native biomass.

WateredUnwatered

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.

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




• 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.



• 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.

Every plant has its own intrinsic ability to acquire vital resources, invasives are just better at it than natives (big bullies).


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?

• Conceptually appealing• Strong evidence for a number of species in many different

habitats (although sometimes invoked without concrete evidence)

Readings for Next Class1.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

what makes a species invasive? is it characteristics of the species ?

Documents

species invasive

plant selfincompatible

selfcompatible pollenasexual

selfcompatible pollenwhat

longseed productiontend

present juvenile period

long fruiting periodwhat

present juvenile periodtend