Most protected areas face risk of invasion by alien animal species living less than 10 kms away, finds study

Over 95% of the protected areas around the world were found to be environmentally suitable for the establishment of at least some of the alien species under investigation

                            Most protected areas face risk of invasion by alien animal species living less than 10 kms away, finds study
Brown rat (Professor Tim Blackburn, UCL)

Protected areas across the globe are aimed at keeping invasive animals at bay, but the large majority of them are at risk of invasions, according to researchers. For most protected areas (PAs), an invasive animal species is living less than 10 km away that is well suited to the protected area's environment, says a report by University College London (UCL) and the Chinese Academy of Sciences. 

An invasive species can be any kind of living organism that is introduced accidentally or intentionally from outside their natural geographic range into an area where they are not naturally present. They can harm the environment, the economy and even human health. These species may kill or compete with native species and destroy habitats among other impacts.

"Invasive alien species are the most common threat to amphibians, reptiles and mammals on the International Union for Conservation of Nature (IUCN) Red List (of threatened species, which is an indicator of the health of the world's biodiversity). They may lead to changes in the structure and composition of ecosystems detrimentally affecting ecosystem services, human economy, and wellbeing," says IUCN. According to IUCN, the movement of people and goods around the world increases the opportunity for the introduction of invasive animal species.

Globally, terrestrial protected areas cover about 15% of the Earth’s land surface. In the current study, published in Nature Communications, researchers investigated 894 terrestrial animal species (including mammals, birds, reptiles, and invertebrates) that are known to have established "alien populations" somewhere in the world. They then assessed whether these species occurred within, or near, the boundaries of 199,957 protected areas across the globe, as defined by the IUCN, including wilderness areas, national parks, and natural monuments or features.

"One of the most harmful ways that people are impacting the natural environment is through the introduction of 'aliens' — species that do not occur naturally in an area but have been taken there by human activities. Invasions by alien species are regarded as one of the top five direct drivers of global biodiversity loss, and aliens are establishing themselves in new areas at ever-increasing rates,” says co-author Tim Blackburn, professor at the Department of Genetics, Evolution & Environment, UCL, in the analysis.

The team found that less than 10% of the protected areas are currently home to any of the invasive species surveyed, suggesting that protected areas are generally effective in protecting against invasive species. But almost all of those areas could be at risk of invasion, as an invasive species was found within 100 km of the boundaries of 99% of the protected areas. For 89% of the protected areas, there was an alien species resident within 10 km of the boundaries. More than 95% of the protected areas were found to be environmentally suitable for the establishment of at least some of the alien species under investigation.

American mink was found in 1,251 protected areas. (Professor Tim Blackburn, UCL)

“We find that more than 58% (520/894) of alien animal species have become established in PAs, but in only 9.1% (18,110) of the 199,957 PAs, even though more than 95% of all PAs are environmentally suitable for establishment by at least some of these species. Moreover, our analyses reveal that most PAs are at risk of further incursions by aliens: 89.4% of PAs have populations of alien animals established within 10 km of their boundaries (58% of the alien species), while 99.0% of PAs have populations established within 100 km,” say researchers in their analysis. 

The largest proportion of invaded protected areas was colonized by alien birds (4.7% PAs, 252 species), followed by mammals (3.7% PAs, 91 species), invertebrates (2.2% PAs, 63 species), amphibians (0.5% PAs, 48 species) and reptiles (0.4% PAs, 66 species). The most invaded parks were all found in Hawaii, which includes Volcanoes National Park (80 species), Hakalau Forest National Wildlife Refuge (63 species), and Kipuka Ainahou (62 species).

"Protected areas are a cornerstone of biodiversity conservation, but aliens don't know where their boundaries lie. It's important to know whether these areas might protect against the spread of invasive species. If alien species continue to spread — and we would expect many to do that — many more protected areas will have their boundaries reached, and potentially breached, by these alien species," says Professor Blackburn, who is also affiliated with the Institute of Zoology, Zoological Society of London.

Alien species commonly found in protected areas (Nature Communications)

Researchers investigated common factors among protected areas that are already home to alien species. They found that protected areas tend to have more alien animal species if they have a larger human footprint index, due to factors such as transport links and large human populations nearby. The analysis also shows that larger, and more recently established protected areas, tend to have more alien species. Older protected areas tend to be in more remote areas, so they are less exposed to human impacts, say experts.

Based on their findings, the research team recommends increasing efforts to monitor and record invasive alien species that people may bring into protected areas, deliberately or by accident, especially damaging species like the American bullfrog, brown rat, and wild boar.

"Our results demonstrate that more actions are needed to mitigate established alien species and to maintain core functions of protected areas in protecting native biodiversity. Routine monitoring of new introductions from visitors and vehicles entering parks is a key task to prevent the arrival of alien species. Increasing efforts to monitor, identify and eliminate early propagules in PAs and nearby areas are also needed. There is an urgent need to integrate efforts from the scientific community, governments, NGOs, landowners and local stakeholders to develop more effective biosecurity strategies to pre-empt potential further invasions in protected areas under ongoing global change," say experts.

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