L8: Invasive species

Question 1

Define native species

Answer 1

An indigenous species that occur wild in a given region

Question 2

Define alien (introduced) species

Answer 2

A species that has been introduced to a part of the world to which it is not native.

Question 3

Define invasive species

Answer 3

Species that reproduce in large numbers and spread over a considerable area causing damage.

An introduced species has invaded when it establishes a self-sustaining population.

Question 4

Why are Invasive Species problematic?

Answer 4

• Alteration of habitat.
• Change in the diversity, abundance, and distribution of members of the preexisiting natural communities.
• Competition with native species.
• Broad and cascading effects throughout communities and ecosystems.

Question 5

Define invasion

Answer 5

The establishment of a species outside of its natural range

Question 6

Establishment requires…

Answer 6

dispersal across barriers, colonization, and successful reproduction.

Question 7

Implications for Management

Answer 7

1) Ecologically appropriate restoration -> requires the accurate determination of species’ provenance: Is a
species native or introduced to a region?

2) The risk of applying inappropriate management to what are in fact native species
- > wider implications for the classification of invasive species.

3) Small isolated areas such as oceanic islands seem to be especially vulnerable to invasions

Question 8

To expand its range, a species must be able to:

Answer 8

•  Travel to a new area.
•  Withstand potentially
unfavourable conditions during its passage (BARRIERS!).
•  Establish a viable population
upon arrival.

Question 9

According to Williamson and Fitter (1996), how many introduced species actually succeed in the establishment of new populations?

Answer 9

10%

Question 10

What are the generalised stages common to all species invasions?

Answer 10

Species pool
Entrainment 
Introduction 
Colonization
Establishment 
Spread
Integration

Question 11

What are the 3 filters that act as barriers to the establishment of an introduced species?

Answer 11

Biogeographic filter

Physiological filter

Biotic filter

Question 12

What are natural invasions?

Answer 12

Invasions without human influence

Question 13

What do natural invasions require?

Answer 13

Require the removal of either:
• Geographic barrier
The creation of dispersal corridors through glacial retreat, continental drift,
or chance events.

• Physiological barrier
For example a thermal barrier removed by climate change.

Question 14

Mechanisms of introductions: How they travel to a new area?

Answer 14

Anthropogenic introductions:
intentional and/or accidental.

e.g transported via ships

Question 15

Why are island susceptible to invasive species?

Answer 15

Little history with competitors, predators, parasites, or diseases.

Introduced species can directly compete with or prey on native sp.

Species poverty (because of great distances from
continents)

Evolution in isolation

Early colonisation

Small spatial scales, crossroads of international trade

Ecological release (invasive species may arrive without natural pests).

Question 16

What are the main difficulties concerning ecosystem- based adaptation, mitigation and reducing the threat of invasive species?

Answer 16

1) Ensuring ecologically appropriate restoration
- this requires the accurate determination of a species’ provenance- is it native or introduced?

2) The risk of applying inappropriate management to what are in fact native species- a wider implications for the classification of invasive species.
3) Small isolated areas such as oceanic islands seem to be especially vulnerable to invasions

Question 17

Ensuring ecologically appropriate restoration
- this requires the accurate determination of a species’ provenance- is it native or introduced?

How can this be worked out?

Answer 17

Track the vector: look at import/export records.

Look at pathways that airlines and ships utilise.

Assess at genetic composition of the populations in introduced areas and source areas

Question 18

Galápagos and invasive species

Answer 18

• Some of highest extinction rates in the world (64% of vascular plant taxa and 49% of vertebrates are classified as threatened).
• Human influence is believed to be relatively recent (AD 1535) - can realistically describe pre-anthropogenic impact conditions.
• Greatest conservation threats: invasive species, habitat degradation in the highlands, increasing human impact.

Question 19

How many nonnative plants have been introduced to the Galapagos over the last 500 year?

Answer 19

750

Question 20

Research and land management needs

Answer 20

• More understanding of networks and foodwebs
• Focus on key taxa (quolls)
• Strategic land management to allow native populations best
chance of recovery

Question 21

General qualities of an invasive species

Answer 21

Habitat transformer

High abundance (expanding range)

Small body size

High reproductive potential

Good competitors

Social

Plasticity and adaptive evolution

Broad Environmental Tolerance: life history traits that confer superior colonizing ability or ability to acclimate to a wide range of habitats.

Local Adaptation: adapt to local selective pressures.

Question 22

Environments that resist invasion

Answer 22

In harsh climatic conditions and nutrient-poor habitats, invasion levels are low. Introduced plants tend to thrive in nutrient-rich and man-made habitats.

Mountains, cliffs, bogs, dry grasslands and coniferous woodlands: tend to resist invasion.

Question 23

Environments that are prone to invasion

Answer 23

Human-made habitats, coastal and riverine habitats, where nutrient availability and disturbance can be high: more prone to invasion.

Most invaded habitats include broadleaved deciduous forestry plantations, forest clearings or riverside willow scrub habitats.

Islands: little history with competitors, predators, parasites, or diseases.