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