Invasive Species Lecture 2012

8/13/2019 Invasive Species Lecture 2012

1/49

Ecology ofInvasive Species

Ecology 2013


2/49

But we can fight back!!!!


3/49

Zebra mussels

Clog water intakes forindustry, drinking water ($2billion/yr)

Alter food webs by filter-feeding and

cleaning

water

Monopolize substrate andeven encrust livingorganisms


4/49

Garlic mustard( Alliaria petiolata )

Invades moist easterndeciduous forests

Very common in WesternPennsylvania May threaten many

understory herbs


5/49

West Nile Virus

First US occurrence in Fall 1999in NYC

Has been detected in humans,horses and birds

Mosquito-borne Green areas = wild bird cases in

2001

Some speculation this was a typeof terrorist attack


6/49

Asian Tiger Mosquito( Aedes albopictus )

Imported toSoutheastern US in ashipment of usedtires

Vector for denguefever and yellowfever outside of US


7/49

Purple Loosestrife(Lythrum salicaria )

Invades fertile marshesthroughout the US

Threatens many plant and

animal species Forms dense, nearlymonospecific stands

Vectors: Ship ballast,medicinal plant trade, beekeepers


8/49


9/49

-Paul Ehrlich, 1989

Ecologists cannot accurately predictthe results of a single invasion or

introduction event


10/49

Outline

Magnitude of theinvasive speciesproblem

Costs of invasivespecies

Anatomy of aninvasion

Introduction Establishment Growth and Spread

Invasion Theory Escape from natural

enemies

Evolution of increasedcompetitive ability Hybridization Novel weapons Traits

Resource competitionand invasion by PurpleLoosestrife


11/49

Anatomy of an Invasion

1. Introduction to a new environment2. Establishment in the new environment3. Population growth and spread into undisturbed habitats


12/49

Stage 1. Introductions

Natural pathways Air and water

currents. Wildlife

movements.

Human pathways Intentional

Domesticated

animals Horticultural escape

Unintentional Ballast water: common vector

for aquatic organisms Shipping and commerce

Fruit and vegetable imports Emerald Ash Borer


13/49


14/49

Control during the introduction stage

Intentional Introductions Many introduced species are beneficial (crops,

ornamentals, biocontrol species) Only 0.1% of introduced species will become invasive. Risk assessment must be used to determine which

species pose little dangerUnintentional introductions

Never desirable Careful inspection of imported fruits and vegetables Ballast water: force cargo ships to change ballast in

open ocean


15/49


1. Dispersal to new environment2. Establishment in new environment3. Population growth and spread into undisturbed habitats


16/49


17/49

Stage 2: Establishment

Control Options Control is far easier when populations are small Yet there are still too many species to control all of

them. Identification of potential invaders is critical Mechanical control

Mowing, hand removal Chemical control


18/49


1. Dispersal to new environment2. Establishment in new environment3. Population growth and spread into undisturbed

habitats


19/49

Stage 3. Growth and Spread

The cat is now out of the bag Identification of invaders is easy! Once a species is widespread, control is very

difficult Control at local sites is expensive Re-invasion from surrounding area is likely

Effective control requires broad-based, coordinatedeffort


20/49

Stage 3. Growth and Spread

Control options Mechanical and chemical control are poor long-

term solutions Expensive,

global

control is required Biological control is the only cost-effective long-

term option

Many problems associated with biological control


21/49

Biological Control

Assumes that invaders are successful because theyleave their natural enemies behind

Involves seeking and testing many possible agents

Agents chosen are usually highly species specificand heavily damage the host


22/49

Pros and cons of biocontrol

Pro: Long term solution Inexpensive after

agents are established Highly targeted and

species specific

Con: Most efforts fail despite

successful introductions:

insects running amok. Identification of agents is

expensive Agents MAY NOT be species

specific or may evolve andattack species we like


23/49

Why do some species become

invasive?(or, how can we predict which non-

natives pose the greatest threat andthereby target them for control?)


24/49

Invasion Theory

Escape from natural enemies Evolution of increased competitive ability Hybridization Novel weapons Traits


25/49

Invasion Theory



26/49

Escape from natural enemies

Hypothesis: Escape from natural enemies increases theresource competitive ability of invaders

Rationale: Herbivores, predators and pathogens limit the competitive

ability of otherwise dominant species Natural enemies are not introduced with native plants Invaders then can out-compete natives which still have a

herbivore loadEvidence: Biological control Soil-borne pathogens


27/49

St. Johns Wort and Chrysolinabeetles


28/49

Invasion Theory



29/49

Evolution of increasedcompetitive ability

Hypothesis: Invaders succeed because they evolve lowerallocation to herbivore defense when released fromherbivory

Rationale: Darwin

s theory of evolution by natural selectionpredicts that: if there is variability in allocation to defense,and if that allocation is costly, then invaders which haveescaped their natural enemies will evolve lower allocation todefense and thereby become better competitors

Evidence: Little. Only a few tests, all mostly negative.Example: None. However, this remains an active area of

research


30/49


31/49

Hybridization

Hypothesis: Invaders succeed because hybridize andthereby become better competitors

Rationale: The invasion process brings together

related species which are not naturally co-occurringin their native habitats; hybrids often show

hybridvigor

; thus these new hybrids become super-competitors

Evidence: Found in several invaders, including hybridcattail and salt-cedar. Probably not common.


32/49

Example: Salt cedar

Salt cedar: invades riparian

areas throughoutthe arid west

displaces adiversestreamside shrubcommunity

threatens severalspecies includingthe endangeredWillow Flycatcher

At least eight salt cedar species havebeen introduced, including Tamarixramosissima and T. chinensis

The Nature Conservancy


33/49


34/49

Invasion Theory



35/49


36/49

Example: Spotted knapweed

Spottedknapweed(Centaureamaculosa)invades shrublandsthroughout theNorthern

Rockies Converts

diversegrasslands tomonocultures

The Nature Conservancy


37/49


Knapweed producescatechin, which is toxic toplant roots

Catechin: is common in soil ofEuropean but not North

American ecosystems causes widespread death

of plant root cells reduces germination and

growth of North Americangrassland species

(Bais etal. 2003)


38/49


Knapweed and catechin Poorly tested in the field Is unlikely a common mechanism of invasion

because invaders should be susceptible to the

novel weapons

produced by natives The one major field test that found a negative

impact of catechin could not be duplicated in follow-up experiments.


39/49

Invasion Theory


f l d f l


40/49

Traits of plant invaders facilitatetheir dominance

Hypothesis: Invaders possess traits which make them goodcompetitors in specific environments

Rationalization: Invaders succeed because they are bettercompetitors for limiting resources than the native species intheir new environment.

Evidence: UnknownExample: Resource competition theory


41/49

Resource competition theory(Tilman

s R*) provides clear, testable

predictions for both invaders andbiocontrol:

1. A successful invader must deplete limitingresources (light or nitrogen) to lower levels thannative species

2. A successful biocontrol agent must limit theinvader

s ability to deplete limiting resources


42/49

Resource Competition models

0

1

Invader Native

R e s o u r c e a v a

i l a

b i l i t

y

0

1

0 25 50 75 100Insect density

r e s o u r c e

a v a

i l a

b i l i t

y

InvaderNative

Invasion predictedEffective biocontrol at

50 insects/m 2


43/49

Resource competition theory

Can predict which species are likely to become invasive(stages 1 and 2)

Can predict whether biocontrol will succeed BEFORE spending millions to introduce another non-nativespecies, hoping it will control the invader (stage 3)


44/49

Model System Purple loosestrife (Lythrum

salicaria ), an herbaceousperennial from Europe, invadesfertile marshes and wetlandsthroughout the US

Broad-leaved cattail ( Typhalatifolia ) is commonly out-competed and displaced byloosestrife

A leaf-feeding beetle(Galerucella calmariensis ), iscurrently being introduced in aneffort to control loosestrife


45/49


46/49

Methods II:

Grow invasive andnative in competition

Winners and losersshould be predictedby resourcecompetitive abilitiesdetermined above


47/49

Preliminary results

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 20 40 60 80 100Percent loosestrife leaf area damaged

P e r c e n t

l i g

h t a v a i

l a b i l i t

y

Lythrum Low FertilityTypha Low Fertility

Our data show that 17% leafarea damage is required toraise loosestrife's R* abovethat of cattail (arrow). Thissuggests that if we do not seethese levels of damage in thefield, then biocontrol will not besuccessful.


48/49

Potential applied benefits

If successful, this methodology will allow ecologists to: Predict where potential invaders might successfully invade Predict the efficacy of biological control efforts


49/49

Invasive Species Lecture 2012

Documents