Invasive species impacts
Invasive species are a major cause of biodiversity loss – declines and extinctions of indigenous species – around the world. On islands invasive species are considered to be one of the main causes of on-going environmental change.
New Zealand – a tragic illustration
New Zealand, an isolated archipelago of more than 700 islands, provides many dramatic and tragic examples of the ecological effects of alien species invasions. In just a few hundred years more than 40% of New Zealand’s land birds have become extinct – many as a direct result of predation by invasive mammals such as ship rats, feral cats and mustelids (stoats, ferrets and weasels).
In the absence of effective predator control many New Zealand forests have fallen silent and still – the birds, reptiles and large invertebrates have gone. The implications of these changes are only now becoming apparent.
While much of the New Zealand focus has been on invasive animals, alien weeds will threaten over half a million hectares of our high priority conservation land within 10-15 years, mainly by out-competing and smothering native plants. In the longer term, weeds may alter our hydrological regimes, disturb the flow of energy and nutrients, and change the structure and composition of native communities.
Economic and social implications
In addition to their ecological impacts invasive species also have serious economic and social implications – especially in New Zealand where our economy is largely based on farming, forestry and horticulture. Millions of dollars are spent annually controlling agricultural pests like rabbits and ragwort.
Biosecurity measures to prevent incursions of high risk organisms such as the painted apple moth and foot and mouth disease are also prioritised in recognition of the economic and social implications of their becoming established.
