An invasive species is a species which has been introduced to an area outside its natural range and can cause a multitude of ecological, economic and public health problems within the new habitat as its population grows. Invasive species may belong to any taxonomic group, with mammals, reptiles, birds, amphibians, plants, invertebrates, fish and viruses all having invasive populations around the world. The extinctions of numerous species around the world can be attributed to the negative effects of invasive species.
When a species is taken out of its natural range and placed into a new habitat it is removed from its natural predators and any pathogens which help to control its population. Without these, population growth may become out of control and the invader can rapidly colonise its new habitat. The characteristics which enable an invasive species to outcompete native species include fast growth, a short life cycle and the ability to tolerate a wide range of habitat types and environmental conditions. Successful invasive plant species often have high rates of seed production and very adaptable reproductive techniques. The degradation of various habitats around the world has made invasions by non-native species a much simpler process, as it is much easier for them to colonise a disturbed area.
In the UK, populations of invasive species have been introduced from every continent in the world apart from Antarctica. Invasive non-native species can be transported and introduced through a multitude of methods, some intentional and some accidental.
There is a correlation between the increase in global trade and the increase in invasive non-native species introductions. Mountains and oceans serve as natural barriers which prevent the long distance transport of fauna and flora out of their native range, although these barriers have been broken more frequently as transportation has improved. Ships, planes, trains and trucks are used to transport goods throughout the world, and this unwittingly transports fauna or flora into a new area where it may subsequently become invasive. One of the main transport methods of aquatic non-native species is in the ballast water of ships, with three to five billion tonnes of water being transported around the world each year. Non-aquatic species are mostly transported within the cargo of vehicles, especially within wooden packing material which can support populations of damaging plant pathogens and insects. As well as trade, the increase in tourism has also facilitated the spread of many invasive species by enabling them to travel large distances to areas outside of their native range.
Many UK invasive non-native populations have become established in the wild due to individuals escaping from captivity. This is especially prevalent within the horticultural industry where exotic plants have escaped from private gardens into natural areas. Many exotic pets have also escaped or been purposefully released, and a wild population has become established.
As well as accidental introductions, many UK invasive species have been introduced purposefully without consideration for the future ecological consequences. Many fish species have been introduced to aquatic habitats outside of their native range to improve angling conditions, although this has devastated many water systems around the world and has been responsible for eliminating numerous native UK fish species.
The introduction of invasive species can have devastating impacts on an ecosystem and may even lead to the local extinction of native species, especially if they are already endangered. When a non-native species is introduced to a new ecosystem it disrupts the natural food web and may begin to outcompete native species for food, as well as directly predating them. When natural food webs are disturbed, there are very complex and varied consequences, which will ultimately lead to a reduction in biodiversity within the habitat. Competition may also occur between native and non-native species for nesting areas. Hybridisation between native and non-native species can also occur, which results in the reduced fitness of offspring and could ultimately lead to the extinction of the species.
Non-native species can introduce unknown pathogens into their new habitat, which can spread to the native population which has not experienced the disease before and will have no immunity to it. As well as disease being transmitted to fauna and flora, many diseases can also be transferred to nearby human populations.
Many ecosystem processes can be altered by invasive species, including nutrient, water and fire cycles, succession and habitat modification, which can ultimately lead to a decline in biodiversity. Altered water cycles can also increase the risk of flooding in nearby areas.
As well as having large-scale ecological impacts, invasive species can also have economic implications, and £1.7 billion is spent annually in the UK on their control. Direct economic loss may occur from invasive species causing damage to infrastructure or goods, as well as indirect losses resulting from decreased tourism and recreation in affected areas.
The negative effects of invasive species are most evident in island ecosystems, which are much less resilient than mainland areas when affected by invasive species.
There are many techniques being used worldwide to attempt to control the spread of invasive species, including preventative, chemical, biological and legislative methods, as well as education and research.
One of the biggest obstacles with invasive species control is lack of research, and there are large gaps in scientific knowledge. The government in the UK has been researching invasive species for many years in an attempt to control their impacts and investigate strategic methods of eradication. One of the most important methods for controlling invasive species is to raise awareness and educate the public to help them understand the risks involved. This may be achieved by promotion from key organisations and industries to their stakeholders and members. As more members of the public become aware of the harmful effects of invasive species, accidental introductions will hopefully be reduced.
There are many methods already in place to prevent the further spread of invasive species, although they may not be adequate. It is recommended that all imports are inspected to detect non-native species, and this is thought to be one of the most effective approaches to blocking this pathway for invasive species. To reduce the translocation of non-native species through shipping, the International Maritime Organisation (IMO) adopted the International Convention for the Control and Management of Ships’ Ballast Water and Sediments in 2004, which provides two performance standards for the discharge of ballast water. The two standards ensure that appropriate volumes of ballast water are exchanged during the ships’ journey and that the water is treated to remove any organisms.
In the UK, the Great Britain Non-native Species Secretariat (GBNNSS) was formed, which developed a strategy for controlling invasive species. They aim to create public awareness, promote a shared sense of responsibility and provide a national framework for mitigating, controlling and eradicating UK invasive non-native species. The IUCN Species Survival Commission’s (SSC) Invasive Species Specialist Group (ISSG) has developed the Global Invasive Species Database (GISD), which aims to increase awareness of and promote prevention and management techniques for invasive non-native species. The organisation reviewed their strategy after five years to assess its success and develop new ideas. There are also many action groups throughout the UK which are working towards eradicating damaging invasive species from their area. Integrated Pest Management (IPM) is thought to be the most effective form of controlling invasive species. It is used worldwide to prevent the negative effects of invasive species, and usually involves a combination of a few recognised management techniques.
Although many countries involved in international trade have legislation in place to prevent the transport of invasive species into their country, such measures are inadequate. It has been recommended that all countries involved in international trade should attempt to develop satisfactory legal frameworks to protect their native biodiversity from invasive species introductions. There is legislation already in place including the Convention on Biological Diversity (CBD), which is a global agreement covering all aspects of biodiversity and highlighting its importance. Collaboration between international stakeholders is extremely important to address this international problem and ensure it does not destroy global biodiversity.
Preventing the establishment of invasive species before it has happened is the best method for protecting global biodiversity against the harmful ecological impacts of non-native species. Early detection, monitoring and a rapid response are vital to prevent an invasive species from establishing a wild population. If an invasive species is detected before it becomes established it can be extremely simple to remove, although once it has been properly introduced eradication becomes much more difficult and expensive.
Preventative methods are the most economic and ecologically beneficial techniques, being used to eradicate an invasive species before it has had the chance to become established. Eradication of invasive species is extremely costly and difficult, and prevention and fast-action techniques are more successful and cost-effective than any which involve removing established populations. It is extremely rare that risk assessments of species are done before they are introduced into a country, although this preventative measure would be highly beneficial and would prevent the introduction of dangerous invasive species before they have left their native habitat.
Building awareness and educating key groups about invasive species is vital when preventing their transport and introduction. Information on the negative impacts of invasive species needs to be shared throughout the world to help the public to take appropriate action and protect international biodiversity. This may be achieved by the development of new legislation and research, which can then be shared using an appropriate medium depending on what resources are available in the area.
Many measures are currently being taken to prevent the spread of invasive species in the UK, including the Check, Clean, Dry campaign, which is aimed at recreational water users. The guidelines encourage the public to be more active in ensuring that they are not translocating invasive non-native species with their equipment. Be Plant Wise is another campaign which was launched by the Department for Environment, Food and Rural Affairs (DEFRA) and the Scottish Government, which aims to raise public awareness and give advice on disposing of non-native plant species.
Invasive species are a global threat to biodiversity and action must be taken worldwide to control the spread of invasive fauna and flora. There are many ways in which everyone can help:
More information on the impacts of UK invasive species:
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© Mark Boulton / www.ardea.com
Ardea wildlife pets environment
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Tel: +44 (0) 208 318 1401
ardea@ardea.co.uk
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