Alien Species

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An invasive/alien species is an introduced, non-native species present in an ecosystem.

Intentional introduction - where a species is brought in on purpose e.g. cane toad

Accidental introduction - where a species is brought in by accident e.g. rats/spiders travelling in with food imports

Success of alien species:

Alien species are successful in their new environments because;

they have enhanced survival rates because they are more efficient competitors than native species

as an alien species they lack and native predator

they are not susceptible to indigenous diseases

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Japanese Knotweed:

Introduced to Britain in the 19th century as an ornamental plant

Grows up to 1 meter in 4 weeks (3cm a day) pushing through concrete and tarmac

Can lie dormant underground for up to 20 years and a root can spread up to 7 meters

No natural predator and threatens plants and animals

Can ruin house prices - value can half

In 2003 the cost of eradicating it was £1.5 billion, in 2009 it was £3 billion

Have to use industrial strength herbicides and weed killers

Mitten Crabs:

1 of the worlds top 100 invasive species

Accidental introduction - came from eastern Asia and Europe to north England

They caused damage to fishing gear and competed with native species

Destroyed local freshwater species, burrowing nature of crabs damages embankments

Management is difficult due to abundance

Cane Toads:

Introduced to Australia to eat cane grubs and beetles that were damaging crops

Females lay 40,000 eggs, a large number of which survive

They ate everything except the grubs and beetles

Difficult to get rid of because they are poisonous

Have to deny them access to water. Many people run them over in their cars