News / USA

Alien Species Not Always Welcome Visitors

Some non-native species are harmless, but others wreak havoc on other species, human health and the economy

Sea lampreys attach to fish with a suction cup mouth ringed with sharp teeth.
Sea lampreys attach to fish with a suction cup mouth ringed with sharp teeth.


Rosanne Skirble

Not all non-native species are created equal, says ecologist Mark Davis. He wants to do away with the popular view that divides the natural world into two opposing camps - native species and non-native species.  

In an essay in the journal Nature, the Macalester College biology professor joins 18 other scientists to argue that action to protect ecosystems should be based on species impact and not species origin.  

He urges conservation managers to order their priorities around how non-native species impact other species, human health, waterways and the economy.  

“What we should focus on is what is the species doing?" he says. "What are its functions within the community and then (decide) to keep or not."  In some cases those would be non-native species and in other cases, not native.

Davis and his colleagues do not deny that real problem species exist.  “Some of them are native. Some are non-native.  The ones that are non-native we should try to keep them out from countries in which they are not currently inhabiting.  But once the species are in, you often have to learn to live with them.”  

But that’s not always an option. Jennifer Nalbone is director of Invasive Species Navigation with Great Lakes United. The U.S. Canada coalition is dedicated to keeping aggressive invaders out of the lakes, and controlling those already there.  

She points to the on-going struggle with zebra mussels. They arrived in the mid-1980’s in ship ballast water from the Black and Caspian Sea region, and have become a major threat to wildlife, navigation, and boating.  “You could look back in history to the (19)80s and (19)90s in Monroe, Michigan when a power plant and the city’s water supply were shut down because its intake pipes were clogged with zebra mussels. Mussels contributed to a valve problem in the 1990s at the Nine Mile Nuclear Power plant in Lake Ontario.”

Each year zebra mussels cost the region between $100 million to $200 million.

Sea Lamprey is an eel-like fish native to the U.S. Atlantic coast that is also now found in the Great Lakes. Twenty million dollars are spent each year to fight this parasitic pest. Nalbone says with that in mind, the focus is on stopping the next big invader - Asian Carp. “These are burdens that the Great Lakes are struggling under right now and we don’t want another one in the region.”

Yet, she says, the Asian Carp, which can grow up to a meter long and weigh as much as 45 kilograms, is making its way north.  The voracious eater, imported by Midwestern fish farmers in the 1970s, could end up devastating the region’s 7 billion dollar fishing industry.

All that is holding it back now is an electric fence. Nalbone says keeping carp from Chicago is high on her list.

However, not all non-native species pose such a threat.

The large, bell-shaped Devil's claw, which is native to Central and South America, was introduced into Australia in the 19th century.
The large, bell-shaped Devil's claw, which is native to Central and South America, was introduced into Australia in the 19th century.

Take the Devil’s Claw, a Mexican herb that today grows wild in Australia. The campaign to eradicate the weed has mobilized hundreds of volunteers. Despite those efforts, Devil’s Claw persists and Davis says there is little evidence that the ecosystem is at risk.

“This tendency to jump to conclusions, the assumption of negative impacts, that has cost us a lot of money and resources directed to areas where there really wasn’t a lot of harm which meant they were not available to be used on species which were really causing harm.”

Another example is tamarisk. The shrub was imported from Eurasia and Africa in the mid-1800s to control soil erosion in the American Southwest, but it spread to river systems across the West and up mountainsides, to elevations of 2,000 meters.

After tamarisk removal, some land managers are turning to an innovative grow-out method called long-stems.
After tamarisk removal, some land managers are turning to an innovative grow-out method called long-stems.

While millions of dollars have been spent to suppress tamarisk, Davis, says the shrubs are not all bad.

“In fact (they) are now providing important habitat for some of the wildlife there, and if we eradicate them, we are actually making things worse.”

Stacey Kolegas, director of the Tamarisk Coalition, says tamarisk control is part of a coordinated plan for river health. She agrees with Davis that conservation must be science-based and site specific.  

“A community that has monoculture of tamarisk running through their downtown right where their river runs is going to be managing tamarisk for fire mitigation, whereas a wildlife area is going to be managing tamarisk because they want to increase the berry producing shrubs on their land to enhance wildlife habitat.”

You May Like

Video Americans, Tourists, Reflect on Meaning of Thanksgiving

VOA garnered opinions from several people soon after November 13 Paris attacks, which colored many of their thoughts

Video Thais Send Security Concerns Down the River

In northern Thailand, the annual tradition of constructing floating baskets to carry away the year’s bad spirits highlights the Loy Krathong festival

Video Tree Houses - A Branch of American Dream

Workshops aimed at teaching people how to build tree houses have become widely popular in America in recent years

This forum has been closed.
There are no comments in this forum. Be first and add one

Featured Videos

Your JavaScript is turned off or you have an old version of Adobe's Flash Player. Get the latest Flash player.
Belgium-Germany Border Remains Porous, Even As Manhunt For Paris Attacker Continuesi
Ayesha Tanzeem
November 25, 2015 10:46 PM
One of the suspected gunmen in the Nov. 13 Paris attacks, Salah Abdeslam, evaded law enforcement, made his way to Belgium, and is now believed to have fled to Germany. VOA correspondent Ayesha Tanzeem makes the journey across the border from Belgium into Germany to see how porous the borders really are.

Video Belgium-Germany Border Remains Porous, Even As Manhunt For Paris Attacker Continues

One of the suspected gunmen in the Nov. 13 Paris attacks, Salah Abdeslam, evaded law enforcement, made his way to Belgium, and is now believed to have fled to Germany. VOA correspondent Ayesha Tanzeem makes the journey across the border from Belgium into Germany to see how porous the borders really are.

Video Islamic State Unfazed by Losses in Iraq, Syria

Progress in the U.S.-led effort to beat Islamic State on its home turf in Iraq and Syria has led some to speculate the terror group may be growing desperate. But counterterror officials say that is not the case, and warn the recent spate of terror attacks is merely part of the group’s evolution. VOA National Security correspondent Jeff Seldin has more.

Video Taiwan Looks for Role in South China Sea Dispute

The Taiwanese government is one of several that claims territory in the hotly contested South China Sea, but Taipei has long been sidelined in the dispute, overshadowed by China. Now, as the Philippines challenges Beijing’s claims in an international court at The Hague, Taipei is looking to publicly assert its claims. VOA’s Bill Ide has more from Beijing.

Video Syrian Refugees in US Express Concern for Those Left Behind

Syrian immigrants in the United States are concerned about the negative tide of public opinion and the politicians who want to block a U.S. plan to accept 10,000 Syrian refugees. Zlatica Hoke reports many Americans are fighting to dispel suspicions linking refugees to terrorists.

Video After Paris Attacks, France Steps Up Fight Against IS

The November 13 Paris attacks have drawn increased attention to Syria, where many of the suspected perpetrators are said to have received training. French President Francois Hollande is working to build a broad international coalition to defeat Islamic State in Syria and in Iraq. Zlatica Hoke reports.

Video US, Cambodian Navies Pair Up in Gulf of Thailand

The U.S. Navy has deployed one of its newest and most advanced ships to Cambodia to conduct joint training drills in the Gulf of Thailand. Riding hull-to-hull with Cambodian ships, the seamen of the USS Fort Worth are executing joint-training drills that will help build relations in Southeast Asia. David Boyle reports for VOA from Preah Sihanouk province.

Video Americans Sharpen Focus on Terrorism

Washington will be quieter than usual this week due to the Thanksgiving holiday, even as Americans across the nation register heightened concerns over possible terrorist threats. VOA’s Michael Bowman reports new polling data from ABC News and the Washington Post newspaper show an electorate increasingly focused on security issues after the deadly Islamic State attacks in Paris.

Video World Leaders Head to Paris for Climate Deal

Heads of state from nearly 80 countries are heading to Paris (November 30-December 11) to craft a global climate change agreement. The new accord will replace the Kyoto Protocol on Climate Change that expired in 2012.

Video Uncertain Future for Syrian Refugee Resettlement in Illinois

For the trickle of Syrian refugees finding new homes in the Midwest city of Chicago, the call to end resettlement in many U.S. states is adding another dimension to their long journey fleeing war. Organizations working to help them integrate say the backlash since the Paris attacks is both harming and helping their efforts to provide refugees sanctuary. VOA's Kane Farabaugh reports.

Video Creating Physical Virtual Reality With Tiny Drones

As many computer gamers know, virtual reality is a three-dimensional picture, projected inside special googles. It can fool your brain into thinking the computer world is the real world. But If you try to touch it, it’s not there. Now Canadian researchers say it may be possible to create a physical virtual reality using tiny drones. VOA’s George Putic reports.

Video New American Indian Village Takes Visitors Back in Time

There is precious little opportunity to experience what life was like in the United States before its colonization by European settlers. Now, an American Indian village built in a park outside Washington is taking visitors back in time to experience the way of life of America's indigenous people. Carol Pearson narrates this report from VOA's June Soh.

Video Even With Hometown Liberated, Yazidi Refugees Fear Return

While the northern Iraqi town of Sinjar has been liberated from Islamic State forces, it's not clear whether Yazidi residents who fled the militants will now return home. VOA’s Mahmut Bozarslan talked with Yazidis, a religious and ethnic minority, at a Turkish refugee camp in Diyarbakır. Robert Raffaele narrates his report.

Video Nairobi Tailors Make Pope Francis’ Vestments

To ensure the pope is properly attired during his visit, the Kenya Conference of Catholic Bishops asked the Dolly Craft Sewing Project in the Nairobi slum of Kangemi to make the pope's vestments, the garments he will wear during the various ceremonies. Jill Craig reports.

Video Cross-Border Terrorism Puts Europe’s Passport-Free Travel in Doubt

The fallout from the Islamic State terror attacks in Paris has put the future of Europe’s passport-free travel area, known as the "Schengen Zone," in doubt. Several of the perpetrators were known to intelligence agencies, but were not intercepted. Henry Ridgwell reports from London European ministers are to hold an emergency meeting Friday in Brussels to look at ways of improving security.

Video El Niño Brings Unexpected Fish From Mexico to California

Fish in an unexpected spectrum of sizes, shapes and colors are moving north, through El Niño's warm currents from Mexican waters to the Pacific Ocean off California’s coast. El Nino is the periodic warming of the eastern and central Pacific Ocean. As Faiza Elmasry tells us, this phenomenon thrills scientists and gives anglers the chance of a once-in-a-lifetime big catch. Faith Lapidus narrates.

Video Terrorism in Many Forms Continues to Plague Africa

While the world's attention is on Paris in the wake of Friday night's deadly attacks, terrorism from various sides remains a looming threat in many African countries. Nigerian cities have been targeted this week by attacks many believe were staged by the violent Islamist group Boko Haram. In addition, residents in many regions are forced to flee their homes as they are terrorized by armed militias. Zlatica Hoke reports.

Video Study: Underage Marriage Rate Higher for Females in Pakistan

While attitudes about the societal role of females in Pakistan are evolving, research by child advocacy group Plan International suggests that underage marriage of girls remains a particularly big issue in the country. VOA’s Ayesha Tanzeem reports how such marriages leads to further social problems.

VOA Blogs