Transcript Invasive species on islands

Invasive species on islands:
consequences and management options
Thomas Elmqvist
Swedish Biodiversity Centre
Rapa Nui
“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).
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)
Polynesian co-voyager
Rattus exulans
•seed
•bird
predator
predator
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
Island factsinvasions 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
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 Hawaii´s
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
Island vulnerability
• Evolutionary isolation, restricted genetic
diversity
• Ecological release
• Crossroads for intercontinental trade
• Anthropogenic impacts on high proportion
of landscape
• Species poverty?
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”
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
Miconia calvescens
Melastomataceae
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
Myrica faya (Myricaceae)
• Indigenous to the Azores,
introduced to Hawaii, late
1800s
• Shade-tolerant, nitrogenfixing, dispersed by introduced
birds
• Invades all types of habitats,
threatens native species on
nutrient-poor soils, favours
other alien species
• Today cover > 40.000 ha on
Hawaii
Introductions to the Azores
Gunnera
Hedychium garberianum
Invasions after disturbances
Mikonia micrantha
Introduced from South
America
Covering regeneration
after a cyclone and fire
Disturbances after invasions
Alterations
• Fire regime
Example
• Erosion
• Introduced trees increase
• Biotic disturbance
• Pigs increase soil
• Introduced grasses
increase fire frequencies
riparian stream bank
collapse
disturbance
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?
Global Invasive Species Program
1. Global early warning system
•
Global data base
2. Trade as vectors for invasive species
•
•
White list of organisms
Conflict with WTO
3. New approaches for risk analyses
•
Adopt recent risk assessment models
developed for GMOs
Global Invasive Species Program
4. Assessment of best practice for
management and control
•
develop a toolkit for invasive management
5. New approaches for education
•
target oriented to horticulturists, pet trade,
tourist industry etc.
6. Economic consequences of invasions
•
full economic impact yet to be assessed
7. Legal and institutional framework
Adaptive Management
Implementing policies as experimentsprobe the responses of ecosystems as human
behaviour changes
1.
monitoring – modelling – predictions
2.
tests with appropriate control – evaluation
3.
modifying policies and practices
(Holling 1978, Walters 1986, Carpenter et al.
1999)
Invasive species management:
Management option
• Control of immigration
• Early detection and rapid
•
•
•
•
response
Monitoring
Eradication
Limitation of spread
Rescue operations of
endangered species
Islands
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Continents
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