Definition
Invasive species
Invasive alien species are non-native organisms that, when introduced to a new ecosystem, can cause significant harm to local biodiversity.
- Every ecosystem maintains a natural balance developed over thousands of years through ecological succession and co-evolution among species.
- Invasive alien species (IAS) are non-native organisms introduced, intentionally or accidentally, into an ecosystem where they do not naturally occur.
- These species can rapidly outcompete native organisms, disrupt food webs, alter habitats, and lead to the decline or extinction of native species.
While not all introduced species become invasive, those that do often share certain biological advantages such as rapid reproduction, broad diet, and lack of natural predators.
How Alien Species Arrive in New Ecosystems
Accidental introductions
- Through global trade: seeds, insects, or larvae hitchhiking on imported goods, packaging, or ship ballast water.
- Travel and tourism: seeds stuck to shoes or clothing; small animals in cargo shipments.
- Agricultural contamination: pests and weeds transported in crop soil or livestock feed.
- Transportation: ships, planes, and vehicles moving organisms across continents.
Spiders found in fruit shipments or insects carried in wooden pallets can become established in new environments if conditions are favorable.
Deliberate introductions
- Biological control: species introduced to control pests (e.g., cane toads in Australia).
- Aesthetic or commercial use: ornamental plants like Japanese knotweed or animals for aquaculture and farming.
- Recreation or hunting: non-native fish, birds, or mammals introduced for sport.
Japanese knotweed was introduced as an ornamental plant, but now spreads uncontrollably across Europe.
Common Mistake- Assuming that all alien species become invasive.
- In reality, only a small proportion of introduced species establish and spread enough to become ecologically disruptive.
Why Invasive Species Become Successful
- Lack of natural predators or diseases in the new ecosystem.
- Ability to reproduce quickly and in large numbers.
- Generalist diets can eat a wide range of food sources.
- High adaptability to new environmental conditions.
- Aggressive behavior or competitive superiority over native species.
- Invasive species behave like “ecological weeds”.
- Once established, they spread uncontrollably, displacing native flora and fauna
