In pursuit of tiny black ants, Neil Tsutsui and Andy Suarez have traveled up and down California and as far away as Argentina-keeping their faces close to the ground.

The two UC Davis postdoctoral fellows have collected thousands of invasive Argentine ants, isolated and compared their DNA, observed their intercolony fights and other behavior, and traced the historical paper trail to document their spread across the United States.

The integrative approach to their research-from genes to communities-sums up the wide-ranging work at the UC Davis Center for Population Biology. The Center for Population Biology is one of the few research organizations in the world that focuses on the fundamental biological processes underlying changes in populations.

Faculty members, postdoctoral scholars and graduate students who belong to the interdisciplinary center study a variety of plant and animal species-from flowering legumes to seaweed and from butterflies to native California turtles. They use genetic analysis, mathematical models, laboratory experiments and field studies to conduct their research.

Research by Tsutsui and Suarez determined that a long stretch of the state-from Ukiah to the Mexican border-is essentially one happy supercolony of Argentine ants.

And unlike in Argentina, where competition between rival colonies keeps their numbers in check, most of the California imports recognize each other as family. "In ants, usually their biggest competition is within the same species," says Suarez. "But here, colonies are so closely related they even exchange workers."

The ants' lack of genetic diversity is the result of a population bottleneck, Suarez and Tsutsui found. Their close-knit sisterhood and the fact that their colonies have multiple queens have allowed the Argentine ants to displace native ants and become one of California's leading household and agricultural pest.

Argentine ants first arrived in this country in New Orleans around 1891, unintended imports that probably hitchhiked on shipments of coffee and sugar cane, as well as soil used as ballast on cargo ships.

Their descendants traveled with humans across the country, thriving in Mediterranean climates wherever people irrigate their lawns, gardens and farms. They were first noticed in California around 1908.

The collaboration between Tsutsui, an ecologist and evolutionary biologist, and Suarez, an ecologist in the Department of Entomology, illustrates the cross-disciplinary nature of the Center for Population Biology. Their research also reflects the level of independence of the center's postdoctoral fellows and graduate students, says Rick Grosberg, an evolution and ecology professor who directs the center.

"I think the hallmark of our program is that our graduate students work on their own research projects," Grosberg says. "They don't piggyback on their professor's research. Same for our postdocs."

"It's been incredibly successful. As a result, labs often collaborate. Students often work together with the postdocs as a team."

Grosberg's own research focuses on the evolution of kin recognition and social organization in sea anemones and other aquatic invertebrates. He and Tsutsui are collaborating using genetic techniques to analyze ant family ties, and manipulations of family units to understand ant recognition systems. They are also working to understand an unusual system of parental care and cannibalism in a marine snail, where once again, recognition of close from distant relatives is at the heart of the establishment of complex, and sometimes violent, social arrangements. And one of Grosberg's graduate students, Sarah Gilman, is studying how climate change influences abundance of shore populations.

Over the past five years, the population-biology graduate students have brought in a total of $2.6 million in their own grant funding, Grosberg said. Each of the 14 postdoctoral fellows to go through the center since 1993 have gone on to tenure-track faculty jobs at top-level universities.

Maria Servedio, a postdoctoral fellow at the center for the last two years, said she got four offers for faculty positions. She will spend the next year at UC San Diego working on a research project funded by the National Science Foundation before joining the faculty at the University of North Carolina, Chapel Hill.

Servedio's research combines mathematics and biology to develop theoretical models of the genetic mechanisms that discourage one species from interbreeding with another. With a bachelor's degree in biology from Harvard University and a doctorate in zoology from University of Texas, Austin, she turned down a grant from the National Institutes of Health to take her position with the Center for Population Biology in 1999.

She said it was the chance to work with the center's faculty that drew her here, particularly Michael Turelli, chair of the Section of Evolution and Ecology and "one of the best theoreticians" in the field. "There are so many good people here," Servedio said. "There's so much breadth."

The Center for Population Biology is based in the Division of Biological Sciences' Section of Evolution and Ecology, but its membership is campuswide.

The center unites about 35 faculty members, close to 20 postdoctoral scholars and more than 40 graduate students from nine departments: agronomy and range science, entomology, fisheries and wildlife conservation biology, evolution and ecology, environmental science and policy, environmental horticulture, environmental design, geology, and philosophy.

All of the center's faculty members and many of its graduate students also belong to the Population Biology Graduate Group, one of UC Davis' three highly regarded graduate programs focusing on ecological and evolutionary questions.

These graduate programs, which also include ecology and animal behavior, ranked fifth in the nation in the most recent evaluation by the National Research Council in 1995. A study published in the October 1999 Bulletin of the Ecological Society of America found that UC Davis' faculty members in the ecology, evolution and behavior programs lead the nation in the volume and prestige of scholarly journal publications in their fields.

"Even on paper, there's no place that compares to Davis for its scientists in ecology and evolution,"said postdoctoral fellow Tom Near, who uses both gene sequencing and fossil records to calculate rates of evolution in turtles, North American freshwater fish and Antarctic icefish.

Since joining the Center for Population Biology a year ago, Near said he's had the opportunity to interact, on a collegial basis, with a number of faculty members and to collaborate with some "highly motivated, very sharp and very ambitious" graduate students.

e described the atmosphere as "casual but rigorous" with few of the traditional barriers of academic social strata that can isolate faculty members, postdoctoral fellows and graduate students from one another.

"You can rest assured that if you present an idea that it will be scrutinized," Near said. "Feedback will always be presented in a positive fashion. That rigor obviously pushes and challenges you. But the creative atmosphere allows you to be expressive and to take a chance.

"I know that no matter where I end up, I'm going to bring a part of Davis with me," he said. "I think that the philosophy and the attitude, both in terms of how you do science and how you treat other people, is really positive here."

By conducting basic research on populations, the center contributes to the development of sound environmental, public health, and agricultural programs.

Don Strong, an evolution and ecology professor, is part of a team studying Atlantic cordgrass, an invasive plant species threatening West Coast marine estuaries.

At an open house held for some of the center's supporters this spring, Strong described how postdoctoral fellows and graduate students are studying whether native insects or ergot, a fungal disease that damages seed, could be used as biological controls. However, Strong told tour participants that researchers are taking care not to adopt cures that could be as bad, or worse, than the cordgrass. "We're not going to do anything slap-dash or quick. We want to know what's going on."

This year, the center embarked on a campaign to build an endowment graduate-student and postdoctoral fellowships. "The goal is to foster financial independence for research so that our students and postdocs can do the most creative and independent research possible," Grosberg said.

Suarez and Tsutsui, for example, hope to continue their research in some of the other areas around the world invaded by Argentine ants, such as Bermuda and the Pacific Islands. The ants are also problems in the Mediterranean, Hawaii, Southern Australia and South Africa.

Argentine ants cause significant damage in California. In Southern California, they are the leading household pest, ahead of fleas and roaches, Suarez said. They also pose costly problem for farmers because they shepherd aphids for their sweet "honeydew" excretion. The invasive ants also cause ecological damage, killing native ants that are a major food source for native horned lizards and other animals.

Suarez said an ecological balance could ultimately be restored because the Argentine invaders, with so little genetic diversity, might not survive a major climate change. "If you don't mind waiting a few thousand years, there's a lot of hope," he said. "Unfortunately, we don't work on those kind of time scales."

In the meantime, there's another worry. Suarez said Argentine ants, by displacing native species, could pave the way for another destructive invader from South America-the red fire ant, which is common in Florida and Texas and has been found in areas of Southern California.

back to top