March 7, 2003

Scholars eye non-native species invasions

Research takes scientific, humanistic approaches to common cause of extinctions


A professor of environmental science and policy, Susan Harrison, front right, leads a student group to a bank littered with tamarisk plants that have been treated and burned to eradicate them.

Debbie Aldridge/Mediaworks

By Clifton B. Parker

Under a bright winter sky, a couple dozen students and researchers trek through Putah Creek Riparian Reserve on the edge of the UC Davis campus. They’re here to investigate the aliens among us — invasive plants, animals and pests — that constitute one of the biggest ecological challenges of our day and age.

Peter Moyle, a fish ecologist at UC Davis, peers through a pair of binoculars at a Putah creek that is now receiving increased water flows, which benefit native species.

“We’re surrounded by invasive species,” Moyle says. “We’re trying to understand them better, find out how to cope with future invasions and manage the ecosystems where trouble currently exists.”

Today, alien invasions are second only to habitat loss as a cause of species endangerment and extinction. In the past few hundred years, as humanity has settled North America, thousands of non-native plant and animal species have become entrenched on the continent. It’s estimated that invasive species cost the United States more than $138 billion a year.

Safeguarding diversity

Beyond economics, safeguarding the earth’s diversity is driving the concern about invasive species. Native species are often driven to extinction by competition, and invasive species can cause harm to the economy, environment or even humans — consider the West Nile Virus.

The glassy-winged sharpshooter is another intruder that poses a serious threat to California’s agricultural system, especially its grape and wine-making industry. The sharpshooter can transmit the deadly Pierce’s disease to grapevines, and other diseases to almond trees, alfalfa, citrus and oleanders—endangering more than 100 species of plants.

Then there’s Sudden Oak Death. UC Davis plant pathologist David Rizzo has identified how this fungus-like organism has killed thousands of coastal oak trees and threatens the state’s treasured redwoods.

 California also faces invasions by yellow starthistle — “the plant that ate Calfironia” — red fire ants, “killer algae” or Caulerpa taxifolia, cheatgrass, rice blast, Africanized honey bees, Asian clams, Northern pike, the Chinese mitten crab—and these are only a few.

Salmon dreams

Back at Putah Creek, it’s apparent that environmental changes can favor one species or another. Building a dam or diverting water flow for land-use purposes has consequences for plants and animals.

Moyle points out that decreased water flows along Putah Creek — once an active salmon stream — have made it hospitable for non-native species and less so for salmon. Some of these non-native species, for example, feed on the young salmon. In recent years, the university, the city of Davis and the Putah Creek Council have worked cooperatively with the Solano Water Agency to manage flows in the creek to benefit native fishes and discourage aliens.

“Increased water flows benefit native species such as salmon because they seek waters that run deeper, faster and cooler,” Moyle says. “Relatively small but strategic increases in flow have turned what was once a stream dominated by alien fishes to one dominated by natives.”

Humanity is an issue as well.

“We’re the ultimate invasive species,” he says. “Along with ourselves we’ve brought many favored species into new environments. It’s a form of cultural imperialism that has scientific ramifications.”
David Robertson, an English professor, is leading this trip along with Moyle. Robertson is a faculty member in the Nature and Culture program, an interdisciplinary set of studies allowing students to explore the complex relationships between human cultures and the natural world.

“Our environment cannot be understood without looking at all the ways that human beings have tried to make sense out of the world: literary, religious, social, economic, scientific, political,” Robertson says.

He notes that the humanities and social sciences need to join with the sciences to increase our understanding of complex issues.

“Creative ways to explain this problem exist beyond spreadsheets and data — we have stories to tell to people,” he says.
Robertson motions to some familiar-looking eucalyptus trees on the banks of the nearby Putah Creek. The tree seems as common in California as coastal oaks. But in this Ellis Island of the plant and animal world, common doesn’t equate to native.

“Many Californians are surprised to find out that eucalyptus trees are non-native species from Australia,” Robertson says. “We almost accept alien species as native because they’ve been here so long and are part of the landscape many of us grew up with.”

Robertson and a dozen or so other faculty members are infusing this “holistic” approach into the campus’s new Biological Invasions IGERT or “Integrative Graduate Education and Research Traineeship.” Made possible by a National Science Foundation grant, this interdisciplinary program is training students in the ethical, political, legal, economic and scientific issues connected to biological invasion.

Kevin Rice, an ecology professor and co-chair of the IGERT, says, “We’re training students from all backgrounds: the life sciences, social sciences, engineering, physical sciences and the humanities.”

Caz Taylor is studying for her doctorate in ecology and is a participant in the Biological Invasions IGERT. “We have to engage the public and explain why it’s important to care about native species,” she adds. “I’m not sure if we’ve reached that critical mass yet where it becomes a societal priority—though it needs to be.”

Toward the South Fork of Putah Creek, Moyle and Robertson lead their group to “Restoria,” which is the product of a restoration effort led by Dan Leroy, (M.S. ’01), when he was a graduate student. Though it recently suffered a fire, the site includes native trees and shrubs planted by volunteers and students. Before this project, Restoria was just a litter-filled area marred by off-road vehicles and dominated by non-native species.

Restoration of such a site, Robertson says, requires much dedication and work in watering and weeding. “It’s about making a vision of native species come true.”

McLaughlin Reserve

A similar vision is at work a hundred miles north at the Donald and Sylvia McLaughlin Reserve.

A few weeks after the Putah Creek trip, UC Davis researchers and students headed to the reserve, which at 6,800 acres is the largest of 34 such reserves in the UC system.

Susan Harrison is an environmental professor and campus director of the Natural Reserve System. During spring, she makes the long, winding drive a couple times a week from Davis around Lake Berryessa to the reserve.

“The reserve offers students in this program a unique opportunity to actually manage native and exotic species and thus to examine the real-world applications of their academic knowledge,” she says. “The IGERT students are designing an invasive species management plan that will be implemented by the reserve’s managers, Paul Aigner and Cathy Koehler.”

Doctoral students Kara Moore and Sarah Elmendorf are conducting an experiment to understand the establishment and spread of invasives.

On a large hill created by the rocks pulled from the mine and now covered by non-native grasses, Moore and Elmendorf have planted 100 small patches of mustard seeds to see how much the plant spreads and how much its invasion success depends on “initial conditions.” That means determining how many mustard seeds arrive at a site and how disturbed the site was when those seeds arrived. Also, they will introduce another batch of seeds one year from now.

“We’d like to know if the game is over once the invasive species settles in,” says Elmendorf. “In other words, how much does repeated invasion matter?”

Tough questions

Research on invasive species occurs throughout campus by faculty from the Division of Biological Sciences, College of Agricultural and Environmental Sciences, School of Veterinary Medicine, College of Letters and Science and even the School of Law.

Holly Doremus is a professor specializing in environmental law. Originally a research scientist before her law career, Doremus has explored how legislators can use scientific information to bolster laws like the Endangered Species Act.

The legal implications of trying to control invasive species raise intriguing issues.

“How do we decide if it’s worth the effort?” she says. “And who sets the standards on controlling invasive species? Clearly, this issue can overlap into international, national and state areas of concern.”

 Defining which species belong in an ecosystem is sometimes based less on science than on historical, cultural, moral, geographic or theological arguments. Some scientists question the scientific wisdom of trying to roll back exotic species.

They even contend that alien species often fit into their environments.

Michael Rosenzweig, a professor of evolutionary biology at the University of Arizona, says that the distinctions between exotics and native species are artificial.

“You can’t roll back the clock and remove all exotics or fix habitats,” Rosenzweig told the New York Times.

“Both native and exotic species can become invasive, and so they all have to be monitored and controlled when they get out of hand.”

Of the country’s 7,000 alien species — out of a total of 150,000 species — only about 10 percent are invasive. The other 90 percent have fit into their environments and are considered “naturalized.” Still, some ecologists would say appearances are deceptive, and many of these aliens may be considered acceptable only because no one has documented their harmful effects.

Peter Moyle agrees that society cannot get rid of all invasive species. Rather, it’s a matter of degrees, and that means using science and policy to prevent or diminish future invasions and managing the environment to favor natives over non-natives.

He points to the Chinook salmon as one example. “If we lose the salmon, we lose part of ourselves.”


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