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Living With Invaders

Updated Tuesday 24th August 2004

The impact that the invasion of exotic plants and animals has had on the British Isles - living with invaders

Impossible to eradicate, many invaders are here to stay. Learning how to manage them so that they do as little damage as possible has been helped by studies of the ecology of invaders. Biological research is important in determining how we manage current invaders, and which exotics will become the invaders of the future.

Managing Invaders

With eradication often impossibly expensive and time consuming, management is the next best thing. This involves reducing the numbers of the invader to levels where they do minimal harm. Management is usually expensive, laborious and has to be repeated continuously so understanding the biology of invaders is vital in creating management plans that work.

Bringing in pests and diseases from the invader’s native habitat can be one way of reducing populations of invaders. Known as biological control agents, these additional introduced species can be very effective. However, introducing one exotic species to control another is not without dangers. The life history and habits of the biological control agent have to be carefully researched or you may end up with two invaders instead of one.

One man’s invader is another man’s friend

Invaders are defined as being pests. Being a pest is a subjective distinction and whilst some species are unanimously thought of as invaders, there can be contention whether many species are invasive pests or not. Some of our oldest invaders, such as the rabbit (Oryctolagus cuniculus, L.), have established important roles in our native communities. Although still a pest to agriculture, rabbits provide an important food source for native predators such as buzzards (Buteo buteo, L.) and foxes (Vulpes vulpes, L.), and their grazing actually helps maintain plant biodiversity.

Behind the times – Invaders waiting in the wings?

Most invaders in the British Isles today were introduced a century or more ago. Muntjac deer (Munaticus spp.) introduced at the turn of the century, were thought to be harmless for 90 years and it is only in the last decade or so that they have been regarded as a pest species. The ring-necked parakeet (Psittacula krameri, Scopoli, 1769), established in 1969 after escaping from captivity. A study of its population in England, showed that it is currently increasing at rates of more than 20% a year, with numbers in 2002 estimated at 6000 individuals. Could this be an invader of the future?

Invaders and a changing climate

A change in temperature or the amount of rainfall can make the difference between an exotic species being able to survive and breed or not. Rapid changes in environmental conditions could also mean that native species no longer have ideal conditions, and could make communities more vulnerable to invasion. Whilst it is difficult to predict how many of the exotic species currently in the British Isles could become invasive if conditions changed to their advantage, we can be sure that whatever the the future holds, invaders are certain to remain a part of it.

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