What are the problems caused by alien species?  

Non-native, exotic, or alien species are those that do not naturally belong in a particular environment, but have been introduced, intentionally or accidentally, by the activities of humans. In many cases introduced species will not thrive as they are not adapted to their new environments. However, of a minority that can survive in their new home, some can become problematic, in extreme cases becoming serious pests. 

At a global level, the impact of non-native species is a grave issue posing a significant threat to biodiversity. Non-native animals and plants can become problematic in environments where they have no natural predators, allowing them to increase their populations to levels that have severe impacts on native species, ecosystems and even human activities. Non-native species that thrive in their new environments are sometimes referred to as invasive exotics.  Two examples from the amphibian and reptile world are cane toads in Australia and brown snakes on Guam. 

A less apparent problem caused by aliens lies in diseases that they may carry, but to which local species have little or no resistance. Such diseases may be partly responsible for the decline of amphibians globally. The impact of such disease in Britain is not fully understood but a precautionary approach to non-native species may reduce any such risks.

In most cases, non-native amphibians and reptiles are not known to pose significant threats in the UK. In part this may be because our temperate climate limits the reproductive potential of many non-native, cold-blooded vertebrates. However, some are able to thrive in our climate and may be significant predators or competitors of native wildlife. An example is the bullfrog from North America, which is major predator within environments to which it has been introduced.  Globally, it is regarded as one of the most problematic invasive alien species. Therefore all efforts should be made to prevent this species becoming established in Britain. There are also growing concerns about the impact of terrapins on waterfowl and fish.

Climate change could alter the success of non-native species in the UK.  We want, therefore, to keep a close eye on the fortunes of alien amphibians and reptiles, finding out where they occur, whether they are establishing breeding populations and whether they are likely to increase in numbers in the future.

Amphibians and reptiles are not the only aliens you might find in your local pond - there are non-native plants out there too. To find out more, take a look at Plantlife's Plant Invaders reporting scheme, which includes two plants associated with waterways - Indian balsam and New Zealand pygmyweed.

Also see what can I do to help with the problems posed by aliens?