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 humans. In most cases introduced species do not thrive as they are not adapted to their new environments. Of a minority that can survive in their new home, however, some can become problematic, in extreme cases becoming serious pests (or 'invasive').
Specifically, invasive non-native species may outcompete, or prey on locally occurring plants and animals. A less apparent problem lies in diseases that non-natives 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 most 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. So every effort should be made to prevent this species becoming established in Britain.
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.