FROM THE VICE PRESIDENT
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LOST LEWIS AND CLARK
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A HAZARDOUS WORLD
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Vision is published annually by The University of Montana Office of the Vice President for Research and Development and University Relations. It is printed by UM Printing & Graphic Services.
PUBLISHER: Daniel J. Dwyer. MANAGING EDITOR AND GRAPHIC DESIGNER: Cary Shimek. PHOTOGRAPHER: Todd Goodrich. CONTRIBUTING EDITORS: Brianne Burrowes, Brenda Day, Judy Fredenberg, Joan Melcher, Rita Munzenrider, Patia Stephens and Alex Strickland. WEB DESIGN: Patia Stephens. EDITORIAL OFFICE: University Relations, Brantly Hall 330, Missoula, MT 59812, 406-243-5914. MANAGEMENT: Judy Fredenberg, Office of the Vice President for Research and Development, 116 Main Hall, Missoula, MT 59812, 406-243-6670.
Why don't all plants flower and seed every year?
By Joan Melcher
Imagine you’re a Bitterroot milkvetch plant living on a south-facing slope in Southwestern Montana’s Big Hole Valley. Life is good. You’re small in number — in fact you and your comrades in Idaho’s nearby Lemhi Valley make up the entire population of Bitterroot milkvetch in the world.
For a few years, a man appears in the spring to walk through your wildflower blossoms, counting, stopping occasionally to poke around at you. OK, so you’ve been found, but he’s not so bad and he only comes by once a year.
Then she shows up. Pretty soon she’s sticking flags next to you, sitting for hours while bees stop by, taking notes while you’re pollinated, calling you Astragulus scaphoides, watering you like crazy a couple of years — in March no less — and then the final insult: She brings others who do even more, including a woman who actually presses your leaves into an electrical device, scribbling while she crimps.
She would be Elizabeth Crone, a 30-something mathematical brain and wildlife ecologist who is more likely to remind one of a teenager on a lark than a lab-coated professor pointing to an inverse variation equation.
Crone, an associate professor in UM’s College of Forestry and Conservation, became interested in milkvetch while she was teaching at the University of Calgary in the late 1990s. She learned about the work of Peter Lesica, author of “Flora of Glacier National Park,” who had been monitoring milkvetch since 1986. Lesica, an independent consultant known regionally for his work on plant conservation and restoration issues, is working on a book on the flora of Montana.
When Crone became interested in the milkvetch, Lesica turned his data over to her. Crone has a doctorate in botany from Duke University, and her doctoral thesis was on chaotic patterns in plant reproduction.
She suspected she had a species worthy of study with Astragalus scaphoides, which flowers generally every other year and is of a vast family of plants that includes more than 500 species in North America. Moreover, this Astragalus, like many, only grows in a small area of the world.
Crone was interested in solving questions associated with plants that mast seed — that is, flower and seed every other year or every three to seven years. Many plants and trees do mast seeding, but the best known are oaks and pines. Beargrass is a well-known plant found in Montana that is a mast seeder. Generally, it flowers and seeds every seven years.
When Crone began her studies, there were two theories about mast seeders — that they do it because it’s good for them (e.g., pollination is more efficient) or because of climatic conditions (e.g., it’s a wet spring).
Crone decided to test the second hypothesis and did heavy watering of a plot of Astragalus in 2001 and 2002. Her research showed little difference in the plants that received extra water compared with those that didn’t.
Then she learned of the work of Akiko Satake, a Japanese theoretical ecologist. Satake had created a model that showed mast seeding is mathematically chaotic, meaning that the way plants allocate resources causes random-looking fluctuations between high and low years of flower and seed production.
As she relates her work and progress, Crone lets the story unfold like a mystery — with her as the detective. She relates every turn, every setback and every breakthrough in a manner that makes them as exciting for the listener as they obviously are for her.
Discovering Satake’s model was one of those exciting moments for Crone because it was close to what her monitoring of Astragalus had shown for a decade. It also countered theories held by plant ecologists — that mast seeding is tied to weather and climate patterns.
Satake’s model described how stored resources change over time within a plant and predicted how much plants flower and set seed as a function of stored resources and pollen availability. Crone was definitely intrigued, but to test the idea on a milkvetch, she would have to kill it, and dead it would be of no use. So she decided to try to solve an inverse mathematical problem. She assumed the model developed by Satake was true and she worked backward, mathematically — for two years.
She measured the number of seed pods a plant produced, assumed stored resources to predict seed production and from there guessed how stored resources change over time, given changes in seed production.
“One of the things I like most about my job is figuring out how math is relevant to ecology,” she says.
After two years, she had a mathematical equation but was still stymied. Her Astragalus production chart was not yet matching her theory. She was trying to write a computer algorithm with the help of Leo Polansky, a former UM technician, when she noticed that, although most plants flowered every other year, some plants flowered every year and some plants flowered only once every four or five years.
“This is not surprising, because there are lots of reasons some plants might be able to gain more resources than others,” she says. “The problem was the models weren’t fitting because of another principle from mathematics — the average of a function is not the function of an average.”
Uh-huh. The average of a function is not the function of an average. OK, Elizabeth, but could you tell us what you really mean?
“Basically, there are two approaches to modeling resource use in plants,” she says, explaining that the average of a function — the method most commonly used by ecologists — estimates one average rate of nitrogen gain and depletion across all plants. The function of the average model [what she and Polansky used] estimates rates of nitrogen gain and depletion for each plant and then uses these predictions to predict for the whole population.
When she and Polansky used the function of an average in the algorithm, “everything fell into place,” says Crone.
The quintessential scientist, alone so long in her curiosity and yearning, Crone beams as she relates her discovery. “What I didn’t take into account was the variation in nature,” she says. Again she and her theoretical ecologist colleagues had turned accepted science on its ear.
Then Crone learned about the work of another researcher, David Kelly, an Australian studying a New Zealand bunchgrass (Chionochloa pallens). He and his colleagues had developed methods for solving a similar but simpler inverse problem analytically rather than numerically, as Crone had done. His models correspond with Crone’s, with some modification to include effects of pollen limitation and differences among individual plants.
Crone suspects, from her work to date, that nitrogen is a key limiting factor in the biennial flowering of milkvetch. Pollination also plays a key role. When many plants of a species are flowering, the likelihood and success of pollination increase. That means a milkvetch only makes seeds — and only depletes its resources — when it flowers in the same year as other milkvetches.
Today Crone is testing the hypothesis. Her research includes a control group, a press group — where the inflorescence (flower) is removed every year to provide seeding -— and a pulse group, where flowers were removed in 2005, a high-flowering and seeding year in the usual cycle of the milkvetch.
Plants in the press group have had their flowers removed every year since 2005. What this does is allow the plant to store nitrogen because it is not being used for making seeds. If Crone is right, the control group will flower in 2005 and 2007. The press group should flower every year. The pulse group should flower in 2006 and 2007, but not 2008. So far, the milkvetches have followed the predictions.
There are many applications where Crone’s findings could be of use. For instance, they could help Anna Sala, an associate professor in UM’s Division of Biological Sciences and the woman pressing the Astragalus leaves when this story started.
For years Sala has studied the whitebark pine, which is threatened by new and invasive diseases. The whitebark pine is a main, late-season food source of the grizzly bear. Its decline could contribute to grizzlies spending more time in lower elevations and possibly meeting more humans. Study of the tree also has implications when scientists consider delisting the grizzly bear as an endangered species.
Sala uses a $35,000 LI-COR 6400 to measure photosynthesis — the way Astragalus leaves take carbon from the air. That will help her and Crone determine how plants gain and release resources and how that relates to flowering and cone production. Like Astragalus, whitebark pine trees produce cones roughly every other year, with big crops every four or five years. If Sala and Crone can predict mast years in pines, the knowledge will help biologists and rangers who want to gather the cones for propagation.
Crone and Sala have three years left on a research grant of $500,000 from the National Science Foundation to compare mast seeding in Astragalus and whitebark pine. Besides that grant, Crone is the lead researcher in two other ongoing projects and has grants for five projects that are led by doctoral students.
She collaborates with Sala and six other UM professors on various projects and works with nine graduate students and six undergraduates in the field and in wildlife biology and ecology programs.
In addition, she’s went to Finland in August on a Fulbright Scholarship to study with mathematician Otso Ovaskainen and preeminent ecologist Ilkka Hanski.
Alas, milkvetch, she’ll be back in the spring.