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Invasive Alien Species on Islands

Invasive alien species are the major threat to islands by most metrics, and two open access papers published this week highlight this threat in different ways. In Nature Ecology and Evolution Wayne Dawson and colleagues identify global hotspots of alien species richness, and find islands and coastal continental areas are most strongly invaded. They also determine taxonomic group pairings which occur disproportionately often, such as birds with mammals, or vascular plants with spiders. New Zealand is identified as a particular hotspot for all possible combinations of taxonomic group pairings.

Hotspot and coldspot regions for cross-taxon established alien species richness
Hotspot and coldspot regions for cross-taxon established alien species richness (Source: Nature Ecology & Evolution)

Meanwhile, myself and colleagues from Island Conservation and the IUCN Invasive Species Specialist Group review invasive alien species on islands in Environmental Conservation. Analysing the distribution of invasive alien species on 33 small island developing states we found most invasive alien species are only on a few islands. However, we identify the 15 most widespread invasive alien species on islands. Most of these invasive alien species are plants, and outside of the tropical SIDS they are also widespread on other islands such as New Zealand. We also review the diverse impacts invasive alien species have on islands, and their interactions with other global change threats.

Species Name Type Origin
Leucaena leucocephala White leadtree Tree Central America
Casuarina equisetifolia Ironwood Tree SE Asia to Australia
Paratrechina longicornis Longhorn crazy ant Ant Tropical Africa
Rattus rattus Black rat Rodent India to SE Asia
Adenanthera pavonina Red bead tree Tree India to S China
Psidium guajava Common guava Tree Central America
Gliricidia sepium Quick stick Tree Central America
Kalanchoe pinnata Air plant Herb Madagascar
Tapinoma melanocephalum Ghost ant Ant Tropical Africa and Asia
Culex quinquefasciatus Southern house mosquito Mosquito Tropical Americas
Cyanthillium cinereum Little ironweed Herb Tropical Africa and Asia
Jatropha curcas Barbados nut Shrub Central America
Mus musculus House mouse Rodent Central Asia
Oreochromis mossambicus Tilapia Fish Southern Africa
Portulaca oleracea Purslane Herb Africa and Asia

Both studies highlight the factors which correlate with higher invasive and alien species richness on islands, namely gross domestic product (wealth), population size and density, and island area and coastline. Both studies also emphasise the important role biosecurity must play in slowing the rate of introductions, and eradications must play redressing the impacts of invasive alien species on islands.

Biosecurity for intercepting invasive alien species on islands
Biosecurity for intercepting invasive alien species on islands (Source: Environmental Conservation)

All these topics will be covered in depth at the Island Invasives conference being held in July 2017 in Scotland.

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