ECOLOGISTS LOOK AT RELATIONSHIP BETWEEN YELLOWSTONE'S WILLOWS AND STREAMS

Photo:  Yellowstone Stream.  From: Wikimedia.

FROM:  NATIONAL SCIENCE FOUNDATION 
Earth Week: Whither Yellowstone's willows and the streams they shade?

Yellowstone's water table dropping below riverbank willow trees
Willows and streams. In Yellowstone, where there's one, the other isn't far behind.

On Earth Week, scientists are asking: How far do such connections reach?

New research on water-dependent willows shows that streams and willows may be conducting the music on Yellowstone's ecological dance floor.

Ecologists Tom Hobbs, Kristin Marshall and David Cooper published the results in a recent issue of the Journal of Ecology. Hobbs and Cooper are with Colorado State University (CSU) in Fort Collins, Marshall is at NOAA.

After wolves were extirpated from Yellowstone almost 100 years ago, elk multiplied, says Hobbs. The herbivores roamed across the landscape, nibbling willows to nubbins.

But the story doesn't end there.

With fewer willows to gnaw on, beavers began to decline. Crucially for willows, without the dams beavers build, which slow the flow of water, streams ran faster. Brooks soon became deeply carved into their banks from the force of rapidly-moving water.

Before long, the water table fell below the reach of streamside willows' roots.

Wolves and elk, beavers and willows: carefully choreographed parts

"All the possible interactions among plants and animals in nature are impossible to separately identify and measure," says Henry Gholz, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funds the Yellowstone willow research through its Long Term Research in Environmental Biology (LTREB) Program.

"Yet scientists know these links are critical to the maintenance of functional ecosystems."

Over a 30-year-period, Hobbs and colleagues studied riparian willow (Salix spp.) establishment and stem growth. In Yellowstone's northern range, the scientists reconstructed willows' history from tree rings. The three-decade time-frame covered the reintroduction of wolves in 1995.

"What happens to willows is shaped more by how high the water table is," says Hobbs, "than by any other factor."

The finding shows how complicated ecosystem links can be, says Gholz. "The effects of elk browsing on streamside willows in Yellowstone over the past 30 years are related more to variations in year-to-year climate, age of the willow trees, and changes in streams due to declining numbers of beavers."

The scientists used climate variables such as annual precipitation, stream flow and growing season length; the abundance of herbivores (elk); and landscape elevation and an index of "topographic wetness" (how soggy the ground is) to predict willow growth before and after the reintroduction of wolves.

"Explaining variability in [willow] establishment required models with stream flow, annual precipitation and elk abundance," write the ecologists in their paper.

"The results show that changes in the growth of willows after the reintroduction of wolves," says Marshall, "can't be understood without considering all the variables."

Life as a willow: water required

Picture a willow as it leans over a river or stream. Willows, sallows and osiers form the genus Salix, made up of some 400 species of deciduous trees and shrubs. All are found on moist soils in cold and temperate regions of the Northern Hemisphere.

Most are known as willows, but some narrow-leaved shrub species are called osiers, and broader-leaved species are referred to as sallows, from an Old English word derived from the Latin term salix.

Willows are the dominant riparian, or riverside, woody vegetation in Yellowstone and across the Rocky Mountains, according to Hobbs.

In Yellowstone, willows are found along rivers and streams, as well as near springs, seeps and anywhere water is available.

"As long as willows' roots can reach groundwater," says Hobbs, "the trees can survive--and withstand very high levels of browsing by elk. It all comes down to water."

On Earth Week and every week, the dance of life needs all the partners

Restoring an ecologically complete ecosystem in Yellowstone requires the return of willows--and with them, beavers, says Hobbs.

Once willows have returned, beavers will gnaw down a certain number of the trees to build dams. The dams will slow stream flow, allowing yet more willows to grow.

Willows, streams and beavers; wolves and elk. Willows and streams may have the first dance. But without them all, Yellowstone's ecological music will eventually fade away.

-- Cheryl Dybas
Investigators
Fred Watson
David Cooper
Jennifer Hoeting
Matthew Kauffman
N. Thompson Hobbs
Related Institutions/Organizations
Colorado State University

THE THINGS THAT LIVE WHERE NO THINGS SHOULD

Hot spring in Yellowstone.  Credit:  Wikimeidia Commons.

FROM: NATIONAL SCIENCE FOUNDATION
How to Thrive in Battery Acid and Among Toxic Metals
In the movie Alien, the title character is an extraterrestrial creature that can survive brutal heat and resist the effects of toxins.

In real life, organisms with similar traits exist, such as the "extremophile" red alga Galdieria sulphuraria.

In hot springs in Yellowstone National Park, Galdieria uses energy from the sun to produce sugars through photosynthesis.

In the darkness of old mineshafts in drainage as caustic as battery acid, it feeds on bacteria and survives high concentrations of arsenic and heavy metals.

How has a one-celled alga acquired such flexibility and resilience?

To answer this question, an international research team led by Gerald Schoenknecht of Oklahoma State University and Andreas Weber and Martin Lercher of Heinrich-Heine-Universitat (Heinrich-Heine University) in Dusseldorf, Germany, decoded genetic information in Galdieria.

They are three of 18 co-authors of a paper on the findings published in this week's issue of the journal Science.

The scientists made an unexpected discovery: Galdieria's genome shows clear signs of borrowing genes from its neighbors.

Many genes that contribute to Galdieria's adaptations were not inherited from its ancestor red algae, but were acquired from bacteria or archaebacteria.

This "horizontal gene transfer" is typical for the evolution of bacteria, researchers say.

However, Galdieria is the first known organism with a nucleus (called a eukaryote) that has adapted to extreme environments based on horizontal gene transfer.

"The age of comparative genome sequencing began only slightly more than a decade ago, and revealed a new mechanism of evolution--horizontal gene transfer--that would not have been discovered any other way," says Matt Kane, program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"This finding extends our understanding of the role that this mechanism plays in evolution to eukaryotic microorganisms."

Galdieria's heat tolerance seems to come from genes that exist in hundreds of copies in its genome, all descending from a single gene the alga copied millions of years ago from an archaebacterium.

"The results give us new insights into evolution," Schoenknecht says. "Before this, there was not much indication that eukaryotes acquire genes from bacteria."

The alga owes its ability to survive the toxic effects of such elements as mercury and arsenic to transport proteins and enzymes that originated in genes it swiped from bacteria.

It also copied genes offering tolerance to high salt concentrations, and an ability to make use of a wide variety of food sources. The genes were copied from bacteria that live in the same extreme environment as Galdieria.

"Why reinvent the wheel if you can copy it from your neighbor?" asks Lercher.

"It's usually assumed that organisms with a nucleus cannot copy genes from different species--that's why eukaryotes depend on sex to recombine their genomes.

"How has Galdieria managed to overcome this limitation? It's an exciting question."

What Galdieria did is "a dream come true for biotechnology," says Weber.

"Galdieria has acquired genes with interesting properties from different organisms, integrated them into a functional network and developed unique properties and adaptations."

In the future, genetic engineering may allow other algae to make use of the proteins that offer stress tolerance to Galdieria.

Such a development would be relevant to biofuel production, says Schoenknecht, as oil-producing algae don't yet have the ability to withstand the same extreme conditions as Galdieria.

-NSF-