One hundred of the worst Invasive Alien Species have been identified in the Global Invasive Species Database. These have been selected at a global level according to two criteria: their serious impact on biological diversity and/or human activities, and their illustration of important issues surrounding biological invasion.
Among the one hundred worst global species, some negatively impact Europe. A recent report by the European Environment Agency, in partnership with IUCN ISSG, presents a number of species which affect Europe’s biodiversity, economy, health and ecosystem services.
A first example is the Rabbit (Oryctolagus cuniculus), a highly successful colonizer native to Southern Europe (Iberian Peninsula) and possibly Northwest Africa now widely spread throughout Europe. Rabbits are an excellent example of the complex effects that an introduced mammalian may exert on the ecosystems to which it has been introduced. By overgrazing, they manage to deeply degrade the habitat they live in, which in turn results in the alteration of the composition and local abundance of animals and plants. Introduced rabbits impact on native fauna, both directly and indirectly, via a range of differing mechanisms (such as competition for food and shelter) which may combine and result in population crashes or extinctions of native species.
The Grey Squirrel (Sciurus carolinensis) introduced in the British Isles and Italy from North America and currently widely spread both in Italy and in Great Britain, as in many other parts of the globe. Originally, the animals were imported and deliberately introduced for ornamental purposes into parks, woodlands and estates. Today they represent a well documented case of alien species impacting both the agriculture sector and the forestry industry, as well as the forest ecosystem. In Italy, the species can have significant economic impact on maize, hazelnut crops, poplar plantations and, potentially, vineyards. While, in the United Kingdom, damage to forestry is huge, with an estimated reduction of the value of tree crops by about 25 % or GBP 10 million per year, while the estimated current annual control cost for timber protection is over GBP 5 million per year. Besides economic damages, the Grey Squirrel competes with the native Red Squirrel for food, causing a dramatic decline of range of the native species in all invaded areas.
The Chytrid Fungus (Batrachochytrium dendrobatidis), better known as the Bd fungus, has had grave impacts on amphibians. The spread of Bd has driven and will continue to drive amphibian species to extinction at a rate unprecedented in any taxonomic group in human history. Bd can apparently be transmitted simply by a combination of animal‑to‑animal and environment‑to‑animal transmission affecting the ability of infected amphibians to respire or osmoregulate through their skin, resulting eventually in cardiac arrest. It is estimated that about 92 % of amphibians considered 'Critically Endangered' by the IUCN Red List of Threatened SpeciesTM are undergoing declines that might be linked to Bd. Human movement of the Bd-infected amphibians is known to contribute to the introduction of the pathogen on the European continent, where it is now spread in at least 17 EU Member (read more on the BiodivERsA Policy Brief "Wildlife diseases on the increase").
Invasives in EU Overseas
The European Union's mainland is made of its 28 Member States, yet the EU also includes 34 overseas territories. Found in every ocean, from polar to tropical latitudes, they are home to a unique diversity of species and ecosystems of global significance, which are also threatened by Invasive Alien Species (IAS). The following species of Lion Fish are not listed among the 100 worst IAS in the world, yet their impacts on the biodiversity of the Caribbean region are particularly severe.
Two species of Lion Fish (Pterois miles and P. volitans) native to the Indo-Pacific region were introduced in the Caribbean Sea as a consequence to accidental and deliberate releases happened in Florida in 1985. Both species are highly invasive and today they are spread all over the Caribbean region. The Lion Fish is a generalist predator and is on top of the food chain in the region which means that its population can reach high densities (500 animals/hectare). By predating other species and/or competing with others for resources, the Lion Fish has severe direct impacts on native fishes and crustaceans. However, this introduced species not only causes ecological issues, but it also affects economic and social aspects of the Caribbean region. In fact, the Lion Fish can directly decrease fish stocks of species of high economic value, with great consequences on commercial and subsistence fishing. Moreover, as it is a venomous species, it can also affect the diving tourism market, which in the region is estimated to value 2.1 billion US dollars.
Later this year, IUCN will publish a new paper on IAS in Europe's overseas to present their impacts on threatened species. The paper will also look into policy options and will give recommendations for possible action.
Information on more IAS can be found in the One Hundred of the World's Worst Invasive Alien Species list, developed within the Global Invasive Species Program (GISP) with the help of IUCN’s ISSG, and in the EEA report. Some case studies of IAS affecting European urban areas can be found here.