Scholarship & Creativity

Updated 10:00 AM Sept. 5, 2006

Scholarship & Creativity

Invasive species alter habitat to their benefit

When scientists study habitats that alien species have invaded, they usually find predictable patterns. The diversity of native species declines, and changes occur in natural processes, such as nutrient cycling, wildfire frequency and the movement of water through the system. But simply observing such changes doesn't prove that the invaders are responsible.

U-M researchers Emily Farrer and Deborah Goldberg have developed a way to tease out the cause of environmental changes in northern Michigan wetlands where invasive cattails have taken hold. They found the cattails alter the environment in ways that hinder native species but benefit invaders.

"When you have an invasion, you typically see three things happening at once: the invasion, the change in environment and the decrease in diversity," says Farrer, a graduate student in Goldberg's laboratory group. "But they're all happening concurrently, so you can't really tell which is causing the other." Other factors may include the use of fertilizers and road salt, and the suppression of natural wildfires. "My question was, are humans causing the changes, or are the invaders?" she asks.

Farrer surveyed marshes and found that hybrids were more common than native cattails. She also noted that the areas of each marsh with lots of hybrid cattails had higher nutrient levels and heavier mats of dead stems than areas with only native wetland plants. Plants growing in invaded areas also were different, with fewer classic wetland species, such as bulrushes, rushes, and sedges, and more typical land plants like grasses, asters, and goldenrods.

The results suggest that invasive cattails set in motion a feedback loop that helps them gain a stronghold. "As the environment changes, the cattails get more abundant and change the environment even more, resulting in even more cattails," she says. "It's interesting—and sobering—to think that it's not just humans that go out and mess up the habitat; invasive species can actually initiate that cycle."
—Nancy Ross-Flanigan, News Service

Diverse pre-cancerous cells can cooperate to produce cancer

If two nearby pre-cancerous cells work together, they have a better chance of surviving and becoming cancer, according to a new analysis.

A diverse collection of tumor cells sometimes can overcome a body's natural defenses more effectively than any one type alone, says Robert Axelrod, a professor at the Gerald R. Ford School of Public Policy and the Department of Political Science.

Axelrod and his colleagues were inspired by game theory, which is a perspective widely used in social science to study the results of interaction between diverse individuals. Their analysis regarding how pre-cancerous cells cooperate with one another raises new questions about how different treatments succeed or fail.

"This analysis does not replace the existing view of cancer as the expansion of one initial cell, but rather this is an additional way of thinking of how cancer develops over time," says Axelrod, the paper's lead author.

For cancer to develop, a series of mutations must occur in a cell's genetic structure. The researchers hypothesize that individual cells do not need to accumulate every trait of a cancer cell to develop into a cancer cell. Instead, neighboring cells actually share their resources. Some tumor cells may provide limited resources that other cells require, allowing for the survival of more cells, which in turn allows mutations to accumulate more quickly.

For example, cancer cells produce certain types of growth factors. One cell may produce one kind of growth factor, while a nearby cell produces a different type. The two cells share growth factors, feeding each other as well as other neighboring cells.

"If you can identify the factors supporting the cells that have not made the complete transition to a full-fledged cancer cell, we can stop those cells from developing. That could potentially become one way to treat the cancer," says Dr. Kenneth Pienta, professor of internal medicine at the Medical School and director of Urologic Oncology at the Comprehensive Cancer Center.

Pienta and Robert Axelrod are the paper's co-authors, along with David Axelrod of the Department of Genetics and Cancer Institute of New Jersey at Rutgers—The State University of New Jersey.

The analysis appears in the current issue of Proceedings of the National Academy of Science.
—Jared Wadley, News Service

Tepid growth predicted for U.S. economy

Although U.S. economic growth has been brisk in recent years, expansion will be moderate through 2008, say U-M economists.

In their annual mid-year forecast of the U.S. economy, Saul Hymans, professor emeritus of economics, and colleagues Joan Crary and Janet Wolfe predict economic growth of 2.2 percent during the second half of this year and throughout 2007—the weakest growth rate in five years. The economy will strengthen somewhat during 2008, posting a 2.7 percent rate of expansion, they say.

According to the forecast, payroll job gains will slip from 1.8 million jobs in 2006 to 1.3 million in 2007. Even though job gains will start to pick up in 2008, on a calendar-year basis, the economy will add just 1.1 million jobs that year.

Unemployment will average 4.9 percent over the next two years, up slightly from this year's 4.7 percent, but still below last year's 5.1 percent.

Inflation will be held in check over the next two years, they say. The all-items Consumer Price Index will move down from this year's 3.7 percent to 3.1 percent next year and 2.7 percent in 2008.

With inflation expected to be contained, Hymans and colleagues believe the Federal Reserve Board will hold interest rates fairly steady over the next two years—after raising the federal funds rate by 25 basis points 17 straight times.

Still, this leaves room for mortgage rates to continue upward, the forecast shows. It calls for the 30-year conventional mortgage rate to increase from an average of 6.6 percent this year—the highest rate in four years—to 7 percent next year and 7.4 percent in 2008.

In addition, the rate for three-month Treasury bills is expected to jump from last year's 3.1 percent to 4.8 percent this year and hold steady at 4.9 percent over the next two years. The 10-year Treasury bond rate, which was 4.3 percent last year, will rise to 5.1 percent this year, 5.7 percent in 2007 and 6 percent the year after.

The U-M forecast also predicts that:

• Oil prices will retreat from recent peak levels, but remain relatively high through 2008;

• Private housing starts will fall from last year's 2.07 million units, the most since 1972, to 1.9 million this year, 1.68 million in 2007 and 1.63 million the year after;

• Existing home sales, which set a new record at 6.17 million homes in 2005, will drop to 5.77 million in 2006, 5.36 million next year and 5.27 million in 2008;

• Sales of light vehicles will edge down from last year's 16.9 million units to 16.7 million this year and then improve slightly to 16.8 million in both 2007 and 2008.
—Bernie DeGroat, News Service

Scientists find 'pinwheels' in Quintuplet cluster

Discovery of pinwheel-shaped dust spirals around two of the mysterious cocoon stars in the Quintuplet cluster tells scientists for the first time that they contain a duo of stars instead of just one.

The spiral shape is a telltale sign of a binary system, which means that it is two lighter-weight stars in orbit around each other, rather than one. Although lighter, these stars still are classified as massive, and each will still become a supernova and provide giant energy pulses in this cluster located near the center of our Milky Way galaxy.

The finding puts to rest the debate among astronomers over these dust-enshrouded stars, says John Monnier, assistant professor of astronomy. It also proves that massive stars in this cluster are smaller than previously thought, and it follows that dust cocoons seen elsewhere in the galaxy likely also are harboring two stars instead of one.

The findings appear in the journal Science, in the paper " 'Pinwheels' in the Quintuplet Cluster." Monnier co-authored the paper with lead author Peter Tuthill, a research astrophysicist in the department of physics at the University of Sydney.

Scientists have debated the nature of the Quintuplet cluster stars, named after its prominent five bright red stars, for years. Until now, however, the stars have been tough to view because they are quite distant and each hidden in a shroud of dust. Astronomers used the world's biggest optical telescope, the Keck in Hawaii, to zoom in on the stars, says Tuthill.

Although still unable to see through the dust completely, the researchers benefited from the enhanced resolution enough to see that the dust formed spiral pinwheels, the same type of dust seen in a type of massive star called a Wolf-Rayet star.

Monnier and Tuthill first identified the characteristic dust pinwheels around this type of Wolf-Rayet star in 1999. Wolf-Rayet stars are thought to be immediate precursors to supernova, the explosion at the end of a massive star's life. Supernovae are rare events, but can be identified across the universe because they produce extremely bright objects made of hot plasma that can be millions of times brighter than the star that exploded.
—Laura Bailey, News Service

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