KEY FINDING 10. Invasive non-native species are a significant stressor on ecosystem functions, processes, and structure in terrestrial, freshwater, and marine environments. This impact is increasing as numbers of invasive non-native species continue to rise and their distributions continue to expand.
Invasive non-native species also called invasive alien species, are species of plants, animals, and micro-organisms introduced by human action outside their natural past or present distribution, and whose spread threatens the environment, economy or society, including human health. Twelve percent of the 11,950 species assessed in Wild Species 2010: the General Status of Species in Canada1 are not native. While only a small percentage of them become established and an even smaller number become invasive, the ecological and economic damage of those few species can be enormous.2, 3 Invasive non-native species harm biodiversity because they can displace native species and compete with them for resources, degrade habitat, introduce diseases, and/or breed with native species to form hybrids. Numerous factors are responsible for the spread of invasive non- native species, including climate change, unintentional introductions from ship ballast and along roads, intentional introductions, and the increased susceptibility of altered or degraded ecosystems. The control of invasive non-native species is expensive and their eradication is seldom possible. They are considered the second greatest threat to biodiversity worldwide, after habitat destruction, and are an emerging threat to northern Canadian ecosystems as climate warms and species intolerant of current northern climatic conditions expand their ranges.