Invasive species on islands: consequences and management options

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Invasive species on islands consequences and
management options

Thomas Elmqvist Swedish Biodiversity Centre
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Rapa Nui
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• The collapse, before European discovery, of the
  obviously highly technological culture
  responsible for the megalithic remains, details
  of which are not known, may be an example of the
  fate of a people who overexploited their resource
  base. These people had no more wood to build
  boats. They had no place to go and not enough
  resources left to live on
• (Mueller-Dombois and Fosberg 1998).

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Ecosystem vulnerability

• Diverse Australian shrub communities show high
  resistance to plant invasions, but are vulnerable
  to introduced pathogens (Hobbs and Atkins 1988,
  Wills 1993)
• Diverse South African shrub communities highly
  vulnerable to plant invasions (Richardson and
  Cowling 1992)

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Polynesian co-voyager

• Rattus exulans
• seed predator
• bird predator

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Invasive species

• alien species which colonizes natural or
  semi-natural ecosystems and threaten native
  biodiversity
• native species extincions, reduced functional
  diversity, altered dynamics of ecosystems,
  reduced resilience
• the second most important factor causing native
  species declines

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Island facts-invasions and extinctions

• Proportion of extinct species that lived on
  islands
• amphibians and reptiles 93
• birds 93
• mammals 29
• Role of invasive species
• rats, pigs and cats responsible for 64 of frogs
  and lizard extinctions and 75 of known bird
  extinctions on New Zealand

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Island facts-

• On Phillip Island, introduced pigs, goats and
  rabbits caused the extinction of 13 indigenous
  plant species, including two endemics
• On Laysan Island, rabbits caused the extinction
  of 26 plant species during a 20-year period
• Alien species chief threat to over 90 of
  Hawaiis endangered plant species, but only 30
  of US mainland endangered species
• On Galapagos, 8 endemic plants have gone extinct
  or are threatened by Lantana camara and goats

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Island vulnerability

• Evolutionary isolation, restricted genetic
  diversity
• Ecological release
• Crossroads for intercontinental trade
• Anthropogenic impacts on high proportion of
  landscape
• Species poverty?

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C. Darwin 1859, pp.337-338

• If all the animals and plants of Great Britain
  were set free in New Zealand, in the course of
  time a multitude of British forms would become
  thoroughly naturalized there, and would
  exterminate many of the natives... Yet the most
  skilful naturalist from an examination of the
  species of the two countries could not have
  foreseen this result

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One invasive species facilitate the spread of
another

• In Hawaii 47 of invasive plant species are
  primarily dispersed by introduced birds and
  mammals
• Red-whiskered bulbul (Pycnonotus jocosus)
  disperse a large number of invasive plants
• Pigs disturb soil and facilitate spread of e.g.
  Passiflora mollisma, Hedychium garberianum,
  Myrica faya

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Miconia calvescensMelastomataceae
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Tahiti

• introduced as an ornamental in 1937
• today widespread in a variety of habitats,
  including wet native forests, covering 75
• fast growing, high seed production, grow taller
  than native trees
• management concentrated on preventing spread to
  other islands

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Myrica faya (Myricaceae)

• Indigenous to the Azores, introduced to Hawaii,
  late 1800s
• Shade-tolerant, nitrogen-fixing, dispersed by
  introduced birds
• Invades all types of habitats, threatens native
  species on nutrient-poor soils, favours other
  alien species
• Today cover gt 40.000 ha on Hawaii

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Introductions to the Azores
Gunnera
Hedychium garberianum
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Invasions after disturbances
Mikonia micrantha Introduced from South
America Covering regeneration after a cyclone and
fire
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Disturbances after invasions

• Alterations
• Fire regime
• Erosion
• Biotic disturbance

• Example
• Introduced grasses increase fire frequencies
• Introduced trees increase riparian stream bank
  collapse
• Pigs increase soil disturbance

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Are ecosystems becoming increasingly susceptible
to invasions?

• Biodiversity and biotic resistance.
• Are species rich ecosystems more resistant to
  invasions than species poor?
• Invasive mutualisms.
• Does the increased rate of introductions result
  in invasive species facilitating other invasions?

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Global Invasive Species Program

• Global early warning system
• Global data base
• Trade as vectors for invasive species
• White list of organisms
• Conflict with WTO
• New approaches for risk analyses
• Adopt recent risk assessment models developed for
  GMOs

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Global Invasive Species Program

• Assessment of best practice for management and
  control
• develop a toolkit for invasive management
• New approaches for education
• target oriented to horticulturists, pet trade,
  tourist industry etc.
• Economic consequences of invasions
• full economic impact yet to be assessed
• Legal and institutional framework

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Adaptive Management

• Implementing policies as experiments-
• probe the responses of ecosystems as human
  behaviour changes
• monitoring modelling predictions
• tests with appropriate control evaluation
• modifying policies and practices
• (Holling 1978, Walters 1986, Carpenter et al.
  1999)

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Invasive species management

• Management option
• Control of immigration
• Early detection and rapid response
• Monitoring
• Eradication
• Limitation of spread
• Rescue operations of endangered species

• Islands Continents
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