Pathways of unintentional introduction and spread of invasive alien species in general
Why is the introduction and spread of invasive alien species a problem?
These days, beside the loss, decrease and degradation of different habitats, invasive alien species represent one of the main threats to biodiversity and related ecosystem services. Invasive alien species always get outside of their natural habitats via human intervention (direct or indirect) where, if the conditions are suitable, they settle (create reproductive, self-sustaining populations), then spread aggressively, eventually transforming the native flora and fauna of the site. Having become invasive, rapid spreading of the species in the new environment is enabled by biological characteristics like quick reproduction rates, wide tolerance against environmental conditions and competitiveness. These species originate primarily from the temperate regions of North America and Asia. The threat to biodiversity and related ecosystem services that invasive alien species pose takes different forms, including severe impact on native species and the structure and functioning of ecosystems through the alteration of habitats, predation, competition, transmission of diseases, replacement of native species throughout a significant proportion of range, and through genetic effects by hybridisation.
Apart from the decrease of biodiversity, the spread of invasive species has also significant health and economic consequences. Transforming habitats, decreasing biodiversity and the degradation of ecosystems (habitats and their communities) have negative effect on the quality of life of mankind. Goods and services offered by the ecosystems and supporting the basic needs of mankind are called ecosystem services. These do not only comprise material welfare; the presence and adequate state of ecosystems (natural species composition, biodiversity) determines the quantity and quality of services they can offer for mankind. Ecosystem services affect our health through the quantity and quality of accessible food, our security (for example by decreasing flood risk) or our state of mind with possibilities of recreation (hiking, resting).
Purposeful and accidental introduction of species to new sites has been known since antiquity but due to the effect of globalization in the last century its extent has grown significantly, causing more and more serious effects. Due to globalization, the scale of the transport of goods is becoming increasingly large. Booming trade and tourism make access to goods easier, but at the same time raise the probability of species being transferred outside their natural habitats. These activities provide a pathway for plants and animals to overcome natural geographic barriers bordering their habitats.
Pathways involve those geographical routes that the species spreads from, as well as the physical routes - such as routes along lines (e.g. road, railway) that the invasive alien species use. But it also involves the mechanisms of spread from the typical activities of different sectors (such as fishery, forestry), which can result in a species becoming invasive. Pathways are closely linked to the activity through which invasive alien species arrive and spread, and their identification is a prerequisite for effective management against the introduction and spreading of invasive alien species.
How do people contribute to the spread of invasive species?
Due to globalization, the scale of the transport of goods is becoming increasingly large. Booming trade and tourism make access to goods easier, but at the same time raise the probability of species being transferred outside their natural habitats. These activities provide a pathway for plants and animals to overcome natural geographic barriers bordering their habitats. One in a thousand introduced species becomes invasive; despite this, along with the constantly growing extent of trade of goods, the number of invasive species grows at an alarming rate.