Invasive Species on Islands: Consequences and Management Options

1. Invasive species on islands:consequences and management options Thomas Elmqvist Swedish Biodiversity Centre

2. Rapa Nui

3. “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).

4. 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)

5. Polynesian co-voyager Rattus exulans • seed predator • bird predator

6. 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 Invasive species:

7. 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

8. 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

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

10. 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”

12. 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

13. Miconia calvescensMelastomataceae

14. 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

15. 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 > 40.000 ha on Hawaii Myrica faya (Myricaceae)

16. Introductions to the Azores Gunnera Hedychium garberianum

17. Invasions after disturbances Mikonia micrantha Introduced from South America Covering regeneration after a cyclone and fire

18. Alterations Fire regime Erosion Biotic disturbance Example Introduced grasses increase fire frequencies Introduced trees increase riparian stream bank collapse Pigs increase soil disturbance Disturbances after invasions

19. 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?

20. 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

22. 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

23. 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)

24. Management option Control of immigration Early detection and rapid response Monitoring Eradication Limitation of spread Rescue operations of endangered species Islands Continents ++ + ++ + ++ + ++ 0 ++ 0 +++ 0 Invasive species management: