Tag Archives: alien species

The brown tree snakes (Boiga irregularis) devastated native populations in Guam. Credit: P Krillow.

Invasive species are responsible for most recent extinctions

When a foreign species is introduced into a new environment, it can wreak havoc on the local ecosystem through competition for resources or direct predation. According to a new study performed by the University College London (UCL), invasive species are the main drivers of extinction in the world, more so than human hunting or agriculture.

The brown tree snakes (Boiga irregularis) devastated native populations in Guam. Credit: P Krillow.

The brown tree snakes (Boiga irregularis) devastated native populations in Guam. Credit: P Krillow.

In the 1950s, brown tree snakes arrived on the island of Guam as stowaways from Papua New Guinea. The only native snake species was a small blind worm-like creature that didn’t bother its neighbors at all. In just a decade, the tree snake had expanded to every part of the island and by 1984, populations of rodents and birds were all virtually extinct. Meanwhile, the tree snake population gained a density of over 13,000 per square mile at the expense of species like the Guam broadbill, which became extinct.

UCL researchers analyzed the International Union for Conservation of Nature Red List — the most reliable database of endangered species — in order to investigate the impact of alien species on native ecosystems. Researchers found that since the year 1500, researchers found that invasive species have been solely responsible for 126 extinctions, representing 13% of a total of 953 global extinctions recorded thus far. Alien species were partly responsible for about 300 extinctions.

In total, 261 out of 782 animal species (33.4%) and 39 out of 153 plant species (25.5%) listed aliens as one of their extinction drivers. In contrast, native species impacts were associated with only 2.7% of animal extinctions and 4.6% of plant extinctions. Overall, the number of extinctions due to alien species is 12 times greater than those caused in part by native species.

“Some people have suggested that aliens are no more likely than native species to cause species to disappear in the current global extinction crisis, but our analysis shows that aliens are much more of a problem in this regard,” lead researcher Professor Tim Blackburn of UCL Biosciences, said in a statement.

“Our study provides a new line of evidence showing that the biogeographical origin of a species matters for its impacts. The invasion of an alien species is often enough to cause native species to go extinct, whereas we found no evidence for native species being the sole driver of extinction of other natives in any case.”‘

Besides alien species, the IUCN Red List identifies 11 other broad categories of extinction drivers, including native species, biological resource use, and agriculture. Biological resource use (i.e. human hunting and deforestation) ranked second on the list behind alien species, having been responsible for 18.8% of lost species.

Among invasive species, the worst offenders were black, brown, and Pacific rats and feral cats. Island habitats were the most vulnerable to invasive species since native species have no alternative home or additional populations.

Plants can also easily drive native species into oblivion. Some have been intentionally introduced for plantations or ornaments for gardens, but once in place, they spread uncontrollably. According to the study published in Frontiers in Ecology and the Environment, foreign plants are several times more likely than native to achieve a maximum cover of at least 80%.

Invasive microorganisms can be just as threatening as more complex organisms. The American chestnut once populated 200 million acres of the eastern United States. However, in the late 19th century, Asian settlers introduced the chestnut blight — a fungus which originally infected the Asian cousin, the Chinese chestnut — and in a matter of decades, all 4 billion trees had been eliminated from the country.

The number of extinctions due to invasive species is likely greater since the origin of some species is unknown, so Blackburn and colleagues assumed that they are native.

“However,” he said, “it is more likely that they are alien. Our results are therefore conservative in terms of the extent to which we implicate alien species in extinction. Also, many regions of the world have not been well studied, and there are likely to be further extinctions that haven’t been captured in these data.”

The findings highlight why biosecurity measures are crucial to preventing the introduction of an alien species, which, in some cases, can be impossible to control once an ecosystem is invaded. Previously, researchers from the Senckenberg Biodiversity and Climate Research Centre analyzed 46,000 recordings of alien animal and plant species that span five centuries, finding 16% of all species have invasive potential. And, let’s not forget that most of these invasive species have been introduced to new environments by humans — ultimately, it is us who are responsible for many extinctions.

Antarctica threatened by alien species invasion

First of all, don’t think of alien species as extraterrestrials; if you came here wanting to hear about that – sorry. Thankfully, the sci-fi scenario is not upon us. I’m talking about species which haven’t originated from Antarctica – seeds, fungi, microorganisms, they go wherever they are taken, and wherever people take them. If you have researchers or some tourists, they can carry a significant amount of intruders, which can be extremely harmful to the aborigen environment.

Preventing is better than treating

There have been numerous examples of intruder species harming a local environment, and even destroying an ecosystem, which is why researchers are paying extra attention to the matter, even when it comes to microorganisms.

“We are still at the stage when Antarctica has fewer than 10 non-native species, none of which have become invasive,” said Kevin Hughes, an environmental scientist with the British Antarctic Survey. “Unless we take steps now to minimize the risk of introduction, who knows what will happen.”

Invasive species often fluorish when brought to a new habitat, and when it comes to bacteria or fungi, some of the most resistant and adaptable creatures in the world, this is definitely a problem you don’t want to cause. Hughes and other researchers have set out to find exactly what has been brought unintentionally to the pristine Antarctic lands by some of the international research teams.

In order to do this, they tested more than 11,250 pieces of fresh produce arriving at nine research stations in the Antarctic and the sub-Antarctic islands; the produce, which included everything you would expect in this case, from apples to pawpaw trees to turnips, was shipped from around the world. What came with it was extremely diverse, including at least 56 invertebrates – slugs, butterflies, aphids, twelve percent of them had soil with them, and more than a quarter were rot from bacterial infection.

An alien problem in Antarctica

“Are these numbers surprising, or does it mean this is likely to be a problem? It’s pretty hard to say,” said Daniel Simberloff, a professor at the University of Tennessee, Knoxville, who was not involved with the research. “The upshot is that there’s just enough people going to some parts of Antarctica nowadays that lots of organisms are carried there. I have to think this isn’t good, and some subset of them are going to pose environmental problems.”

The study was actually part of a larger effort to see exactly what arrives in Antarctica; the bad thing is that there is little that can be done to prevent anything from actually entering, all researchers can do is minimize the risk.

“To be quite honest, the only way we are going to stop the introduction of nonnative species is to stop going to Antarctica, to cut off all the pathways,” Hughes said. “What we can do is try and minimize the risk of introduction and we can do that by relatively simple steps.”

He concluded that the best thing which can be done is to pay more attention to where the food comes from, as well as create a more responsible system of disposing of the leftovers.

So far, alien species have had little success in the harsh environment, with only a tiny fly, the black fungus midge, managing to barely survive in Antarctica, but they might get a little more help from global warming, which will cut from the severity and harshness of the environment.