Nowhere is completely safe from invaders, but some environments have been more affected by them than others. Understanding why some places are more vulnerable to invasion can help us understand the processes involved in invasions and to work out which areas are most at risk.
Are places with lots of species less likely to be invaded?
Biodiverse communities, or those containing lots of species, were once thought to be more resistant to invasion than communities with only a few species. When this idea was tested, by studying the number of invaders in biodiverse and non-biodiverse communities, scientists found that the opposite was true. So why do biodiverse communities have more invaders? We do not know the answer for certain, but biodiverse communities thrive where there is diversity in the habitat. It seems likely that this habitat diversity also provides more opportunities for invaders to find the right conditions to live.
Habitats disturbed by humans usually have high numbers of invasive species. Farmland and areas around cities have been shown to have more invaders than nature reserves or areas of wilderness. Scientists have found relationships between the number of people visiting an area and the number of invaders present. Not every exotic arrival is successful, even for the most invasive of species. So, the more times a species is introduced the higher the chance it will find the conditions it needs to become invasive.
Disturbance can also open up many routes into habitats for invaders. In disturbed areas there can be changes to nutrient levels, grazing, ploughing or even the removal of native species, such as shrubs, that can make the area less favourable for native species. This may give invaders a better chance to establish in these areas.
Next: Can you stop invaders?