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Most countries have made international commitments to tackle this threat, but only half have introduced relevant legislation and even fewer are taking adequate action on the ground. 

Similarly, the pathogenic chytrid fungus, which was entirely unknown until 1998, is thought to be the cause of the decline and extinction of many amphibian populations around the globe. The disease, caused by the fungus, can be spread by humans and a host of other species, ranging from exotic fish to African Clawed Frogs Xenopus laevis.

But the impact of invasive alien species can be successfully controlled. Black-vented Shearwater Puffinus opisthomelas, a seabird native to Natividad Island off the Pacific coast of Mexico, was under threat from cats, goats and sheep. But since they've been eradicated, the status of the bird has been reduced from Vulnerable to Near Threatened on the IUCN Red List. Similarly, the control of the Red Fox Vulpes vulpes in south-western Australia in the last decade allowed the population of the endemic Western Brush Wallaby Macropus irma to recover sufficiently for it to be downlisted on the IUCN Red List to Least Concern.

"It's likely to be more cost effective to prevent the spread of invasive species in the first place than to tackle the biodiversity crisis once they have become established", says Dr Bill Jackson, IUCN's Deputy Director General and Chairman of GISP. "With sufficient funds and political will, invasive species can be controlled or eradicated. This will allow native species to be saved from extinction, but countries need to dramatically improve the way they deal with the problem."