Invasive Species Final

Definition of Invasion + How it differs from other processes

No clear definition (difficult to seperate from natural dispersal/colonization)

Human movement component

• humans move species beyond natural limits

• human mediated invasions occur faster and are more common than natural ones

Major Vectors

Shipping

• ballast water

• fouling communities

• stowaways

• anchor wells

• Packing material

Wood products

• raw wood

• solid wood packing material (SWPM)

Living industries

• horticulture

• agriculture

• pet/wildlife trade

Biological control introduction

Manufacturing chains

Changes in transportation and trade

Invasions driven by movement of people, goods, and communities

Rapid technological change → shifts pathways

Ex: shipping containers increased volume and speed of shipping, trade used to be predominatly with Europe but now is mostly Asia

Future drivers of invasive species

• Climate change

• trade agreements

• economic developement

• technological change

Conceptual Invasion model

Sequence:

Transport → introduction → establishment → spread → invasion

only 1% of introduced species become invasive

Problems with small populations

Extiction vortex

• inbreeding

• genetic drift

• demographic stochasticity

• allee effects

more vurnerable to random events

Environmental stochasticity

Random environmental variation affecting populations

density dependant

can be positive or negative

Demographic stochasticity

Random variation in

• births

• deaths

• survival

• reproduction

more important in small populations

Founder effect

Founder populations

• small subset of original genetic density

• random genotype representation

• inbreeding (increased deleterious alleles)

Genetic paradox of invasion

Invasive species often succeed despite low genetic diversity and inbreeding

Explanations

• genetic purging

• multiple introductions

• phenotypic plasticity

Component Allee effect

individual fitness increases with population size (Ex: poppy in Chile. More plants = more pollinators = more seed production)

Demographic Allee effect

increasing per capita population growth rate with increasing population size. Strong component allee effects can lead to demographic allee effects

Propagule pressure

number of individuals introduced, number of introduction events, interaction between both

Overcomes demographic stochasticity, Allee effects, genetic limitations

Spatial spread

Diffusion- spread within natural dispersal lmits

human-vectored spread- long distance jump beyond natural limits

Stratified diffusion- combination of population growth and coalescence

Lag times

period of low or no population growth after establishment

Caused by maladaptation, environmental change, Allee effects, detectability issues

Sleeper species

Established but not invasive

limited by abiotic or biotic factors

May become invasive due to climate change, disturbance, new genotypes, arrival of mutualists

Invasional meltdown

invasive species facilitate other invasives, creates positive feedback loop, leads to changes in ecology

Ex: Zebra and quagga mussels reengineering the lake bottom and filtering vast amounts of water

Biotic resistance

Native species limit invasion via competition, predation, parasitism, and pathogens

Stronger in diverse communities on a small scale

Enemy release hypothesis

invaders experience decreased regulation by natural enemies leading to increased abundance and distribution

EICA (Evolution of Increased competitive ability)

Reduced investment in defense to allocate resources to growth and reproduction

Introgression

hybrid offspring backcrosses with parent populations leading to genetic swamping and hybrid vigor (increased fitness of hybrids)

Issues caused by invasives

• Replaces native species

• insert into new niches

• 54% of extinctions involve invasives 20% of which are solely from invasives

Biotic changes

Alter trophic structure, simplify food webs, remove species interactions

Abiotic invasions

Alter nutrient or water availability, disturbance regimes, and physical environment

Autogenic ecosystem engineers

alter environment through their structure

Ex: phragmites

allogenic ecosystem engineers

alter environment via activity

Ex: beavers

invasion curve

Eradication

complete removal of propagules, requires early detection and rapid response

Why eradication fails

• Late detection

• insufficient resources

• species already established/spread

• reinvasion

Unintended consequences of removal attempts

• non-target impacts

• predator removal can lead to prey release, mesopredator release

• hyperpredation

Mesopredator release

When the apex predator is removed mesopredators can have greater impact on prey species

Hyperpredation

removal of invasive prey species leads to increased predator populations having a greater impact on native prey species

3 too’s

Too much (invasion too extensive)

Too little (lack of resources or effort)

Too late (detected after establishment)

Control methods

• Mechanical/physical

• chemical

• Biological

• genetic

• integrated pest management

Genetic control options

• breeding natives to become more resistant

• gene drives (genetic engineering tech that forces specific traits to move rapidly through environment)

• high upfront costs

Integrated pest management

• combines multiple control strategies

• developed after reliance on insecticides

• uses chemical, biological, and physical methods together

• goal more sustainable and effective control

Chemical control

• hebricides, pesticides

• cost effective

• can have minimal non-target impacts

• public resistance exists

physical/mechanical control

• picking, cutting, burning, flooding

• limited by scale

• requires repeated effort

Biological control

• use natural enemies

• long term control if successful

• risk to non-target species

• often fails, but high payoff if not

Steps of classical biological control

• suitability

• evaluate

• select

• test

• small release

• large release

• post-release

Slow-the-spread

Used when eradication not possible to delay spread, prepare communities, and buy time

Centrifugal phylogenetic method

test more closely related species first then move on to distant relatives