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MODULE 3. Invasion Pathways. Learning Outcomes. At the end of this module you should be able to: explain why and how introductions occur list some invasion pathways for intentional and unintentional introductions identify what you can do to help prevent invasions.

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MODULE 3

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Module 3 l.jpg

MODULE 3

Invasion Pathways


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Learning Outcomes

  • At the end of this module you should be able to:

    • explain why and how introductions occur

    • list some invasion pathways for intentional and unintentional introductions

    • identify what you can do to help prevent invasions


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What are invasion pathways?

  • A pathway is defined as the means, purpose or activity by which an alien species may be transported to a new location


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Types of introductions

Alien Species Introductions

Intentional

Unintentional

Legal

Unauthorised

Directly released into the wild

Introduced into captivity

Escaped or intentionally released


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Agriculture

  • Cheatgrass

    • introduced to North America for forage

    • displaces native grass species

    • increases fire risk

    • harms livestock


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Forestry

  • Cluster pine

    • introduced to South Africa for forestry purposes

    • forms dense thickets that suppress native plants

    • alters hydrological and fire regimes


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photo by Nickolai Kashulin

Fishing

  • Brown trout

    • introduced worldwide as a sport fish

    • can alter trophic structure by predating upon native invertebrates

    • displaces native fish


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Biological control

  • Indian mongoose

    • introduced to many locations, including Hawaii and Fiji, to control rats

    • predate upon native birds, small mammals and reptiles


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Food

  • Feral pig

    • introduced to many parts of the world for food and sport

    • predates upon birds and invertebrates

    • destroys vegetation

    • distributes weed seeds

      in droppings


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Types of introductions

Alien Species Introductions

Intentional

Unintentional

Legal

Unauthorised

Directly released into the wild

Introduced into captivity

Escaped or intentionally released


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Botanical gardens

  • Miconia

    • introduced to a botanical garden in Tahiti in 1937

    • escaped into the wild and now covers over 60% of the island

    • excludes native plants and causes landslides


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Aquaculture

  • Mozambique tilapia

    • introduced to fish farms for aquaculture

    • released into the wild

    • competes with native fish for food and breeding sites


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photo by Alexander Meinesz

Aquariums

  • Caulerpa taxifolia

    • introduced to Mediterranean, possibly as aquarium waste

    • has spread throughout

      northern Mediterranean

    • smothers native sea grasses

    • destroys fish habitat


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Types of introductions

Alien Species Introductions

Intentional

Unintentional

Legal

Unauthorised

Directly released into the wild

Introduced into captivity

Escaped or intentionally released


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Unintentional introductions

  • The most difficult pathway to monitor

  • Harder still to prevent


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Key Point

  • Unintentional introductions potentially pose a bigger threat to the environment than intentional introductions


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Unintentional introductions

  • The rate of accidental introductions is increasing


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Ship cross-section, showing ballast tanks and ballast water cycle

Globallast Programme (http://globallast.imo.org)

Ballast water

  • A major pathway for marine IAS


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Red tide with dead fish

Ballast water

  • Organisms introduced in ballast water include:

    • toxic dinoflagellates (red tide)

    • cholera

    • jellyfish

    • crabs


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Fouled ship hull

Organisms on a propeller

Pacific Ocean shipping routes 2003-2003

Hull fouling

  • Marine organisms that attach to boat hulls are often transported long distances


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Black-striped mussel

Hull fouling

  • IAS introduced through hull fouling include:

    • Japanese brown alga (Sargassum muticum)

    • Asian kelp (Undaria pinnatifida)

    • black striped mussel


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Key Point

  • Ballast water and hull fouling are the most significant pathways for marine bioinvasions


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Activity

  • Using the Best Practice Manual on IAS Prevention, identify what boat owners should do to help reduce aquatic invasive species being introduced via the hull fouling pathway.


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Tents

Hiking boots

Fishing nets

Personal baggage / equipment

  • IAS can be transferred on personal baggage or equipment

    • seeds, plant fragments, fungi, insects


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Parthenium weed

Seed contamination

  • Occurs when weed seeds become mixed with crop seeds

    • parthenium weed

    • serrated tussock grass


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Vibrio cholerae bacteria adhering to a cell

Packaging material

  • The cholera bacterium was introduced into North America on bait worm packaging material


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Asian long-horned beetle

Formosan termite

Timber

  • Timber and other wood products often harbour invasive insects and diseases


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Brown tree snake

Miconia

Dirty machinery

  • Many species hitchhike on used machinery, vehicles, vehicle parts and military equipment


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Activity

  • What can you do to help prevent new invasions:

    • arriving in your country?

    • spreading within your country?


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Dispersal after introduction

  • Once introduced, an IAS can then disperse into surrounding areas by:

    • natural dispersal

      or

    • human-aided dispersal


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Natural dispersal

  • Digestion / excretion

  • On animals

  • Self-propelled

  • Wind

  • Ocean currents


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Dispersal

  • Ruddy duck

    • introduced into the UK from North America

    • naturally spread into Spain, where it hybridises with the endangered white-headed duck


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Summary

  • Invasion pathways are:

    • mostly man-made

    • numerous

    • incompletely understood

    • increasing


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