FROM THE VICE PRESIDENT
THE FOSSIL TRAIL
Sidebar: New center lands big grant
WOMEN OF SCIENCE
SCIENTIST Q & A
Cover: UM paleontologist George Stanley holds a rhinoceros jaw fossil in the storage room of the University’s paleontology research collection. Found in Montana, the fossil is from the Miocene epoch, which extended from 23 million to 5.3 million years before the present.
Vision is published annually by University Relations and the UM Office of the Vice President for Research and Development. 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, Alex Strickland, Judy Fredenberg, Erik Leithe, Rita Munzenrider and Patia Stephens. 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.
Exotic species alter Montana's landscape
By Chris Bryant
We call them invaders. We try to get rid of them — sometimes by soaking them with powerful chemicals, by unleashing hungry predators on them or — when you can get a group of volunteers together — by simply ripping them out of the ground. But on a large scale, these management actions against invasive exotic species seem like the proverbial little Dutch boy with his finger in the dike.
They have forever — yes, forever — altered the ecological fabric of Montana. But the scope of the present changes happening across Montana’s ecosystem from a handful of strong invaders is staggering, and certainly not limited to pushing out native plants. They have altered fire regimes, disrupted the feeding patterns of creatures from elk to songbirds to spiders, and done things researchers haven’t even gotten around to studying yet. Worse yet, some of our best intentions in the battle against these newcomers prove to have unintended consequences.
Research now under way by UM scientists and others is beginning to help stitch together a new way to look at invasive species — and may help land managers build strategies to help native ecosystems weather the tumultuous changes wrought by the most aggressive of the newcomers.
The Invaders Database System, a Web site maintained by Peter Rice of the UM biology department, details the history and management of numerous species of exotic plants. There one can find, for example, that leafy spurge, a close relative to the dainty holiday poinsettia, vexes would-be eradicators with a rhizomatous root system hidden beneath the ground up to 20 feet from the plant on the surface. A piece of the root as small as half an inch can grow into a new plant. Or that the first documented arrival of this Russian invader in Montana was recorded in 1923 on the Maclay ranch near Lolo.
The page devoted to spotted knapweed says the now ubiquitous plant was first documented in North America in Vancouver, British Columbia, back in 1893. It’s thought to have arrived in the dirt used as ballast on ships. Knapweed, probably the best known of the hated invasives, made its Montana appearance in 1920 in Ravalli County.
These short historical and ecological curiosities are only a small part of the database, which is used by resource managers to develop strategies or educational programs. The new range of some weeds is striking. One example: Just 60 years after knapweed’s introduction, the aggressive invader had found its way into every county in Montana. Today it infests millions of acres.
The prevailing theory behind the success of some of these exotic species in new territories is fairly intuitive. In their native environment, these plants occupy a place within a well-established ecological niche. The plants share space with predators that eat them and jostle for space with well-known neighboring plants, animals and insects — all competing for limited and relatively predictable resources. In an intact ecosystem, organisms have settled into what ecologists call a “dynamic equilibrium.” While the ecosystem is still in some kind of constant flux, after a disturbance — whether it’s a stand-replacing fire or a logging project -- there is a somewhat predictable order in the way a landscape recovers.
But, the theory goes, once weeds are introduced into certain new environments, far away from their natural system of checks and balances, they are able to out-compete naïve native plants. Sometimes these newcomers achieve success to the point of imposing themselves as localized monocultures — basically taking over an entire landscape and evicting the locals. When that happens, the system is far from any state of equilibrium. The upheaval has brought rapid change to the landscape.
Most of the hundreds of exotic species that have settled in Montana are not household names. These “weak” invaders may not act much different than they did in their native ranges, and they certainly have not displayed the kind of negative impacts for which the “strong” invaders are notorious. But a small percentage of these immigrant species — such as knapweed, spurge, Dalmatian toadflax and about a dozen or so others — thrive in their new homeland. It’s this unusual success of a few exotic invaders that grabs headlines and the bulk of the research dollars.
“Nearly all of the attention given to exotic species research is paid to aggressively successful invaders in their new territories,” says Ragan “Ray” Callaway, a UM ecology professor who specializes in the relationships between plants — especially between native species and exotic invaders.
Callaway decided to visit these disruptive invaders on their home turf in order to learn more about how they behave under “normal” conditions.
“I’d heard that spotted knapweed was not that common in Europe [where it comes from],” Callaway says. “I’d gotten directions from a botanist and drove a lot over there. I’d find a little clump of the plant here and there. It was a very minor plant.” Later travels in other European countries showed that knapweed was always a minor member of the ecosystems there.
All plants have novel biochemical signatures — something unique about them that separates them from other species. For example, knapweed roots emit a chemical called catechin that is toxic to most North American plants tested. This trait appears to help make the exotic plant an incredibly successful invader. For some reason, however, knapweed is a relatively meek member of the ecosystem in its home range.
“There are people who say that invasive plants evolve into monsters after they arrive,” he says, “that they change once they come here.”
Callaway and his colleagues have shown that knapweed plants in North America are bigger than those in Europe. However, Callaway believes that post-introduction evolution is not the reason they outcompete our local plants. Instead he argues that knapweed brings a suite of novel chemicals to North America — chemicals to which native plants, insects and soil microbes have not evolved.
Callaway compares the “novel weapons” used in knapweed invasions in the West to the 13th century invasion of central Europe by the Mongols. The Mongols were in possession of an unknown weapon called the recurve bow.
“The recurve bow fired arrows faster, farther and with greater force than anything the Europeans had ever experienced,” Callaway says. “The chemical secretion may be knapweed’s version of the recurve bow.”
While plant invasions are still relatively new to North America, European ecosystems have seen introductions follow in the footsteps of human travelers for untold centuries. According to Callaway, some botanists in Europe believe that older plants incidentally spread by Roman armies may well have shown aggressive invasive tendencies in the past — but even though they are not native, none of them show the traits of aggressive invaders today. However, some new plants that are introduced can become strong invaders. It is likely that some sort of ecological equilibrium works itself out over time.
Callaway has traveled back and forth between Montana and the Caucasus — where another knapweed species called diffuse knapweed comes from — to compare the behavior of the plant here and there. His assumption is that plants in Europe have evolved immunity to knapweed’s novel weapon, and that perhaps some plants here are resistant as well.
Some of his research has suggested that certain native plants already may be developing a resistance to spotted and diffuse knapweed — and that some native predators may be developing a taste for the plant. He speculates that in as little as 100 years, the native components of the ecosystem — from soil microbes to plants to insects — may evolve some strategies to temper knapweed’s unruly behavior.
could be a rule in ecology,” says Callaway, “that if you become
big enough and important enough someone’s going to come after you.
Because that’s where the
spiders and knapweed
If you venture out into an invaded grassland, Pearson says, one of the things you’ll notice are the woody stems scratching at your legs — stems that persist year round. Most of the native forbs in the system die back, but some of the strongest invaders, such as leafy spurge, toadflax and knapweed, all have different structures that change the system in complicated ways. Some native organisms have taken advantage of this change in the composition of their environment.
“We’re looking at a spider that has gone way up in population because it uses those substrates to build webs — it is basically preadapted to the new conditions,” says Pearson. The spider has taken advantage of the invasion and seen a hundredfold increase in its population, resulting in a big hit for native insects and a rapid, unsettling change in the predator-prey dynamics of the system.
For the spider research, Pearson has had to travel all the way out to the game range by Clearwater Junction (about 30 miles outside Missoula) to find “clean” grasslands — ones that have yet to be invaded.
“Even less than 10 years ago I was looking for areas on Mount Sentinel for study sites,” Pearson says. “I found plots that were pretty pristine native bunch grass up there that now I can’t use because they’ve been completely invaded by knapweed.”
His study also requires him to collect spiders that are genetically and maternally unaccustomed to knapweed. To find spiders not already accustomed to weeds, he had to go to the east side of the Rockies where the weeds are less abundant.
“Look how far you have to go to study native systems now, because they are moving away,” Pearson says.
He compares invasive exotic species to a runaway train. “You can stand in front of the train,” he says, “but you aren’t going to stop it. You can switch the tracks. We have tools that are powerful enough to be like a switch operator, but you don’t get the system back to the starting point.”
As a landowner, UM has struggled for years with how to manage weeds. The school owns about 500 acres on Mount Sentinel and another 100 acres near Fort Missoula. According to Marilyn Marler, UM’s natural areas weed manager, invasive species are the No. 1 problem on the land. State law requires the control of weeds deemed “noxious,” and contention over the methods used to control weeds — such as spraying chemicals — led to more discussion than action. But in the last several years some consensus on a management plan emerged, and a host of methods has been employed on the well-used University land.
“We put a lot of emphasis in involving the public,” says Marler, who has spent countless hours talking to service groups, leading education efforts and organizing community weed pulls. The slopes overlooking the University have responded to the efforts.
“When I first started, it was like an old-growth knapweed stand,” Marler says. “Now you can see native plants.” Bluebunch wheatgrass, silky lupine, arrowleaf balsam root and rough fescue are a few of as many as 100 species of native plants you might find in just one acre of the native ecosystem.
One of the primary methods of weed control involves releasing specific organisms that feed only on exotic invaders. Nature is full of such specialists, and 13 of them are actively used against knapweed in the state. The bugs, known also as “biocontrols,” are carefully tested to make sure that they only eat the target plant.
According to Pearson, the long-held assumption has been that a potential biocontrol is safe to release as long as it is host specific, that is, as long as it only eats what the managers want it to eat. But some of his recent research has revealed another layer of complexity to the issue, and brought the criteria used to judge the safety of biocontrols into question.
Pearson looked at a fly commonly used as a biocontrol agent against spotted knapweed. Gall flies lay eggs in the seed heads of knapweed, causing the plant to form a tumor around the eggs. While the fly has been shown to drastically reduce the ability of spotted knapweed to produce prodigious amounts of seeds, Pearson says it hasn’t had much impact on the ability of the plant to spread. What the insect has done, however, is add a substantial food source to the winter menu of deer mice, which feed voraciously on the larva in the seed heads. The mice are carriers of hantavirus, a disease spread by the mouse’s droppings that can be fatal to humans.
Pearson says biocontrols always are evaluated from the perspective of what the biocontrol is eating — not the other way around. Pearson’s research is the first to turn the question around. The introduction of the gall fly, a biocontrol that has been in use for more than 30 years, has caused an ecological chain reaction that couldn’t have been predicted by using traditional biocontrol safety standards.
Pearson says he thinks biocontrol is still an important strategy in the fight against invasive species, but has his doubts that it has been as effective as some advocates claim.
A dry 2000, when the Bitterroot Valley burned, led him to believe that the timing of rainfall might have as much, or more, impact on the spread of knapweed than the fact that it has become free of its natural competitors. That year, Missoula’s rainfall was about 12 inches, not far off normal. But very little of that rain fell in May or June, when knapweed sends up its flowering stalk.
“What I observed in that year is knapweed crashed all over the place,” says Pearson, “and the natives responded very positively at that time.”
Pearson says that biological control efforts were getting some of the credit for the decline in knapweed, but he thinks it was actually the result of an unusually dry spring. In an attempt to prove his hypothesis, he has set up research plots where he carefully controls the timing and amount of precipitation and measures the effect on knapweed.
This research has not made him well-loved by staunch advocates for biological control. But in the end, he says, the important thing is to figure out why some invasive species can become so spectacularly successful.
“What we do know,” says Callaway, “is that it’s the breakdown of evolutionary relationships that allow the ecological community to be invasible. We know now that evolution is so much more diffuse and rapid than we used to think.
We also know that we have not seen the end of new species coming into the region.
“We live in a world where massive shifts in people occur from continent to continent,” says Callaway.
So time may be the ultimate solution to the invasion of exotic species plaguing Montana and the West — time for the ecosystem to adapt to the newcomers while we do our best with research, spraying, biological controls and weed pulling. But says Callaway, “We need to pick our fights.”
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