Invasive alien species (IAS) are plants, animals or micro-organisms outside of their natural geographic range whose introduction and or spread threatens biodiversity, food security, human health, trade, transport and or economic development. They pose the second biggest threat to biodiversity globally, and in certain ecosystems notably islands, the greatest threat to biodiversity. IAS have reached all corners of the globe and impact biodiversity in many ways. The cost of damage caused by invasive species is estimated as US$ 1.4 trillion per annum – close to 5% of global GDP.

 A pressure-state-response model was used in which four indicators were developed and expressed for the purpose of assessing progress towards the 2010 Biodiversity Target for this threat to biodiversity:

Three of the indicators are measured at a country scale and aggregated up to global scale. As a result they can be disaggregated to examine the status of invasion and trends in international and national policy at regional and national scales. The Red List Index is expressed globally, but may be applied nationally.

Future development for the indicator will include increasing the number of countries and taxa for the invasion pressure indicator (and expression of trends therein) as well as updating the policy and Red List indicators. As more national scale information becomes available, response indicators that directly reflect on-the-ground action against IAS (management effectiveness) should be developed (e.g. control of pathways, operational management plans, extent of invasion) (McGeoch et al. 2010).