Biological communities are enormously complex. Every species, native or alien, vies for limited space and resources. If one species runs amok, unexpected things can happen.

When spotted knapweed was introduced into western Montana, the normally benign plant took over the grassland community, crowding out other species. When scientists brought in a native enemy of knapweed in an effort to control its spread--the gall fly--the knapweed population continued to thrive. And then the mouse population exploded.

Dean Pearson, a research ecologist with the U.S. Forest Service, helped untangle the mess with his discovery that dear mice were feeding on the gall fly larvae in the seed heads of the plants.

Pearson's training in wildlife biology and ecology was, of course, essential to his insight. But his background helped too. “Socioeconomically, my family was very poor. But in terms of the environment, Montana is a rich and amazing place. That was really a big factor for me growing up,” he says. He spent lots of time hiking river bottoms and canyons in the Bitterroot Mountains, "just watching nature. I was always looking, always watching things, and being very inquisitive about who was doing what and why."

For years, Pearson struggled to carve out a niche for himself in his community, dropping out of school, fathering a child while still very young, experimenting with drugs, and moving from low-level job to low-level job. The natural environment was always a lifeline, and in time its study provided direction. Today, as a wildlife biologist for the National Forest Service and a presidential award winner, he travels the world studying the complex interactions that play out in ecological systems.

Lost in the woods

Pearson grew up "in a trailer on the side of a dirt road." Raised by a single mother, he and his siblings moved frequently. He attended three grade schools before landing in the Bitterroot valley region. His mother worked hard as a switchboard operator, a motel desk clerk, and a clerk at a second-hand store. "I was often catching fish to help put food on the table and doing odd jobs to help us get by," Pearson says.

The family's moves in and out of small, close-knit communities made it difficult to make close friends. He spent his time wandering the river bottoms and mountains. He remembers walking through the Cottonwood gallery forest, listening to birds. "I was acutely aware of how poor we were," he says. "But I was just as aware of how nourishing and nurturing for me it was to get out in nature. It was very nonjudgmental and very honest."

He fled high school, dropping out shortly after turning 16. "I just didn’t feel like I was getting anywhere. I didn’t feel productive."

Having no particular dream or direction, he worked a number of odd jobs--drilling water wells, cleaning carpets, working in a gas-station diner. He got into "various sorts of trouble." He became a father at 17. He experimented with drugs. "I was just lost," he says. "Lots of teenagers are disillusioned, but I guess I got myself into a hole by that point in time."

With his mother's encouragement, he signed up for a summer program for troubled youth. There, he painted school buildings and curbs and helped build an obstacle course for firefighters. He received $600 for his work. He gave the money to his mother to help pay bills.

Through the program, he met a counselor who pointed him toward an alternative high school that offered an accelerated learning program. He went back to school.

The program was "stripped down," Pearson says. "Basically, we focused on English, history, and math and tested our way through those subjects until we hit whatever level the state standards mandated." He graduated--with a real diploma and not a GED--several months before his old high school classmates. At his counselor's urging, he enrolled at a local community college.

A scientific niche

"I had been involved with some rough characters and involved with drugs. ... I was hooked up with people who were ending up in jail, and eventually some of them died," he says. In retrospect, he sees enrolling in community college as a milestone, but "I really didn’t know what I was doing at that point," he says.

One day, Pearson sat down with his college adviser to choose a major, going down the list alphabetically. There were no majors that started with x, y, or z, so his search ended at w, with wildlife biology. He spent several quarters at the Flathead Valley Community College in Flathead, Montana, "doing mostly prerequisite stuff," then transferred to the University of Montana, Missoula.

It didn't take him long to discover that he "was miles behind your average entry-level college student. I was way out of the loop there and way behind, and realized I had a lot of work to do," he says. So he did a lot of work, including odd jobs on the side to help support his mother and his child. He soon caught up--and surpassed--his schoolmates. He graduated with honors in 1992, receiving the Outstanding Senior Award and the President's Recognition Award from the university’s president.

Stumbling on knapweed


(Courtesy, Dean Pearson)

Dean Pearson at Calf Creek Falls in Escalante National Park, Utah

He also received a scholarship to attend graduate school, but instead of wildlife management, he studied zoology. "It took me a while to realize [that] the classic management of wildlife wasn’t really my thing," Pearson says. "I was much more interested in the science and in learning how animals interact with their world."

He obtained a master’s degree in zoology in 1995 and switched fields again, from animals to plants. His interests migrated toward systems and how species come together and create a community. "Finding my path in science was a bit like the Darwinian natural selection process," he jokes. "I think that’s the case for many people: You figure out best what you want by figuring out what’s not quite right and then getting more and more specific about your direction."

He stumbled, almost literally, onto the knapweed system while working on his master’s degree. He had taken a group of undergraduate students up a hillside behind town to measure the local flora. While the students were busy with their task, Pearson did what he does best: wandering about, observing. He examined a patch of spotted knapweed and noticed seed heads scattered on the ground in small piles. "I was doing work with small mammals, and to me the piles looked like signs of rodent activity, as if small animals had been eating on the seed head," he says.

It was widely believed that nothing ate spotted knapweed; that’s why it had become so invasive. Pearson set out some traps. He caught some mice and looked in their stomachs. They were full of gall fly larvae, which live in the knapweed seed heads.

The discovery led to his Ph.D. work, which determined that mice numbers had tripled because they were feeding on the gall fly biocontrols. Deer mice carry hantavirus, a viral infection spread by the critters' urine and droppings. Hantavirus can cause a pneumonia-like disease that is sometimes fatal to humans.

For years, scientists assumed that as long as a biocontrol agent didn't directly attack anything it wasn't supposed to attack, it was safe for the ecosystem. Pearson showed that even if a species interacts with its intended target as planned, it still may cause unforeseen disruptions.

Pearson was recognized earlier this year with the Presidential Early Career Award for Scientists and Engineers.

The big picture

Today, Pearson is a research ecologist with the U.S. Forest Service at the Rocky Mountain Research Station in Missoula. His studies on spotted knapweed take him to South America and Turkey to study "what allows a species that is a mild-mannered plant in Europe to become a sort of monster in North America or South America." There are applications for ecological management, of course, but for Pearson, it's personal. "To watch a species that has never been in a particular system get tossed into the system, where the organisms in those communities have been sorting things out for the last 10,000 or 11,000 years, is incredible. You get to watch ecology happen before your eyes and see how communities arrange themselves."

"I’m still wandering around and observing. But now, thanks to my training, I’m able to get in there and tease the system apart and do something about it," he says.

Helping others find a healthy niche

Earlier this year, as he was flying to Colorado to accept an award from the Forest Service for a paper he wrote, Pearson struck up a conversation with the young man seated next to him, who was returning home from school for troubled teens.

"I could tell him my own story, which was ... not dissimilar from his story. I was able to talk to him and tell him that he really did have decisions to make," Pearson says. Pearson saw how eagerly the young man "ate up what I had to say." The event made him realize that he was in a unique position to advise young people who are struggling.

He's planning a trip back to Missoula, where they have a number of these schools for troubled youth, to talk to the students. "Knowing those people and having grown up around those people, I know that you can’t come in with a Ph.D. and a fancy title and convince them of anything," he says. "But if you come in and tell them that you started out in the same place, you can ... make them realize that it really is just a matter of decisions and choices that they make themselves. I think that you can get pretty far."

Susan Gaidos writes from near Portland, Maine.
10.1126/science.caredit.a0900142