Yup, even our sweet house cats are a destructive invasive species. Photo via Lincolnlog via Flickr CC
Invasive alien species have been measured for the first time in a large scale study that included 57 countries across the globe. The Global Invasive Species Programme (GISP) has released a report showing that, on average, each country has 50 non-native species that are harming the biodiversity in that country. From invasive rats causing the extinction of bird species, to the spread of chytridiomycosis - a pathogenic fungus - causing a radical drop in frog populations, the results of the study are illuminating, and worrisome. The report, entitled "Global indicators of biological invasion: species numbers, biodiversity impact and policy responses," found that, "The number of documented IAS [invasive alien species] per country ranged from 9 (Equatorial Guinea) to 222 (New Zealand), including 2871 country by species records. There was a total of 542 species that were documented as invasive aliens across the 57 countries examined, including 316 vascular plant, 101 marine, 44 freshwater fish, 43 mammal, 23 bird and 15 amphibian species"
The report warns that the number of documented invasive species is actually severely underestimated and when factoring in the damage caused by the species on local biodiversity, the negative impact is increasing. While the number of policies put in place by governments to combat invasive species has increased, only half of countries that have signed on to the Convention on Biological Diversity have national legislation in effect.
"Although IAS pressure has apparently driven the policy response, this has clearly not been sufficient and/or adequately implemented to reduce biodiversity impact."
Edie names a key example: "The Yellowhead, a bird endemic to New Zealand, has suffered considerably in recent years due to a surge in the number of rats.
Two populations of the Yellowhead are now extinct and three more are significantly falling in number, leading to the species to move up from vulnerable to endangered on the IUCN Red List of Threatened Species."
Invasive species aren't the only threat to biodiversity. Agriculture, loss of habitat, hunting and other human activities are also significant factors. However, the two problems impact different species. the report states, "Agriculture was a more important driver for [negative impacts on] birds and mammals, with hunting and logging also more significant than IAS [invasive alien species] for mammals, but for amphibians, IAS were by far the most important driver."
Invasive species are a common topic of debate in the US, with Asian carp and zebra mussels hitting the news most recently, and underscoring how policies are slow to develop. The shipping industry is a common cause of the spread of invasive species, and more effort is going into studying, and eventually minimizing, how cargo ships and tankers spread species from one area to another.