June 12 (UPI) -- Where are alien, or invasive, species most abundant? Where do they have the most success?
According to new research by an international team of scientists, foreign invaders -- both plants and animals -- most frequently take root on islands and among the coastal regions of continents.
In an effort to identify geographical patterns, scientists mapped the distribution of different types of invasive species, including mammals, birds, amphibians, reptiles, fishes, spiders, ants and vascular plants. Their analysis identified 186 islands and 423 mainland regions with high concentrations of alien species.
Scientists measured the largest number of invasive species -- from all groups -- in Hawaii and New Zealand.
"Both regions are remote islands that used to be very isolated, lacking some groups of organisms altogether -- such as mammals, for instance," Franz Essl, an ecologist at the University of Vienna in Austria, said in a news release. "Today, both regions are economically highly developed countries that maintain intense trade relationships. These have a huge impact on the introduction and naturalization of non-indigenous species."
The study -- published this week in the journal Nature Ecology & Evolution -- showed invasive species were most common in regions with dense human populations and high levels of economic activity.
"These factors increase the likelihood of humans introducing many new species to an area," said Dietmar Moser, another Vienna ecologist. "This almost invariably results in the destruction of natural habitats, which in turn allows non-indigenous species to spread. Islands and coastal regions seem to be particularly vulnerable because they occupy leading roles in global overseas trade."
Researchers say stronger conservation programs and trade regulations are needed to protect islands from the ecological degradation caused by the proliferation of alien species.