Over 10,000 years ago following the Ice Age, plants and animals slowly colonised Britain coming from mainland Europe northwards. As sea levels rose, Britain was cut off from the European mainland and became an island. It is the species that had colonised Britain and established themselves during this period that we call native species.
Since then, we humans have introduced many new species of animals and plants to Britain and these are called non-native species. A minority do have serious negative impacts. These species spread causing damage to the environment, economy and health and are called invasive non-native species.
Natural barriers to the movement of species such as oceans and mountains have meant that unique ecosystems have developed throughout the world. Globalisation has expanded the possibilities, extent and complexity of world trade which along with the growth of tourism has expanded hugely the movements of people, commodities and products. New waterways are being built and link to river catchments across Europe and there is an increase in water-based recreation too. This has increased unintentional and intentional introductions of species outside their natural range, and establishment of FINNS away from their co-evolved competitors and predators.