Non-native invasive Species – their impact on the environment

How do invasive species cause harm?

Invasive species can be classified according to their activities and the damage they do. The following table shows one possible classification scheme.

Activity	Example	Activity	Example
Benign or Beneficial species?	Harlequin ladybird	Parasites or pathogens	Dutch Elm disease (photo - UK Forestry Commision)
Competitors of native species	Long- clawed crayfish, Grey squirrel	Alterations to the biotic/ physical environment or habitat.	Coypu, Cane Toads
Contributors to overgrazing	Muntjac deer, rabbit	Those which dilute genetic integrity of a species	Ruddy duck
Predators of native species	New Zealand flatworm*

The damage they do will depend on their activities but can broadly be summarised as damage by:

Competition for resources
Predation
Herbivory (act of plant eating)
Habitat alteration
Disease
Genetic effects such as hybridization (Natural hybridization can create genetic diversity and is important in evolution. Hybridization due to introduced species more often than not compromises genetic integrity of an existing species to the point of causing extinction).

N.B. this classification is a guide only and some invasive species, such as the harlequin ladybird, might fit into more than one section. When originally introduced into North America and Europe for pest control, the harlequin ladybird successfully controlled aphids on a variety of crop types but has now become extremely detrimental to native ecosystems. In the UK it has arrived by accident and is likely to have limited beneficial effects. In fact, there is concern over its impact on UK species of ladybird, with which it is likely to compete for resources, and even predate upon. It might therefore fit better into the competitor or predation section.

What can be done about it?

The Convention on Biological Diversity has broadly recommended a three-stage hierarchical approach.

Stage 1 is to give a priority to prevent introductions of invasive non-native species.
Stage 2 concerns the detection of newly-introduced invasive non-native species and, where appropriate, rapid action to prevent their establishment.
Stage 3 concerns the long-term mitigation measures, such as containment or control, for established invasive non-native species.

Some UK case studies.

Use the Global Species Database to find out about some of the examples above or an invasive species that occurs in your area. Produce an information leaflet for a named species of your choice.
Harlequin ladybirds – a paradox of intentions. Look at www.harlequin-survey.org and www.ladybird-survey.org and look for ladybirds in your area and participate in the national survey
Play the Deadly Plant Invaders Game. Have a look at this and see if this helps you to understand the way in which invasive species cause harm. Another variation can be found at - called Battlefield Earth.

Harlequin Ladybird

*Photo by kind permission of Down Garden Services

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Non-native invasive Species – their impact on the environment

How do invasive species cause harm?

What can be done about it?

Some UK case studies.

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