Tiny gardeners may help spread invasive species

Tiny gardeners may help spread invasive species
Leaf-cutting ants are the gardeners of the insect world, cultivating fungus on the leaf pieces they bring back to the nest. And like their human counterparts, the ants have to deal with garden waste. After they harvest and feed the fungus to the colony, leaf-cutters often discard the organic debris in piles. Refuse dumps like these might seem innocuous or even beneficial, the equivalent of a backyard compost heap. But researchers in Argentina report that leaf-cutter refuse piles can contribute to the spread of invasive plant species. Alejandro G. Farji-Brener and Luciana Ghermandi of the National University of Comahue studied the abundance and growth of two nonnative thistle species along roads in a national park in northern Patagonia. Roadside colonies are abundant in the region, perhaps because there is bare soil for queens to establish nests.
The researchers found that refuse piles had up to nine times more nutrients than normal soils farther from nests. Those nutrients enabled the thistles to thrive: Plants were up to six times as abundant on refuse piles than elsewhere, seedlings were far hardier and adult plants produced up to three times as many seeds. The findings were reported in The Proceedings of the Royal Society B: Biological Sciences.

Made a mindless goof? Blame your brain
A new study8212;by Tom Eichele of the University of Bergen in Norway and collaborators including Vince D. Calhoun of the Mind Research Network in Albuquerque8212;used functional magnetic resonance imaging to look at what goes on in the brain before an error. Participants played a simple game that involved responding to arrows on a computer screen while the fMRI machine measured blood flow and oxygenation in parts of the brain. The idea, Eichele said, was to see if there were 8220;brain activity patterns that would predict whether or not a response would be erroneous.8221;
As he and his colleagues report in The Proceedings of the National Academy of Sciences, no single 8220;blip8221; or event signals an error. Rather, brain patterns start to change about 30 seconds before an error is committed. The changes were seen in two brain networks. One, called the default mode region, is normally active when a person is relaxed and at rest. When a person is doing something, like playing the game, this region becomes deactivated. But in their experiments, the researchers found that in the time leading up to an error, the region became active again 8212; the subject was heading toward a relaxed state. Another network in the right frontal lobe gradually became less active, the researchers found. This is an area in the brain thought to be related to cognitive control, Eichele said, to keeping 8220;on task.8221; Dr. Eichele said it might be possible someday to develop a warning system8212;perhaps by monitoring the brain8217;s electrical activity8212;to alert users when they are heading for a harmful or costly, not to mention mindless, mistake.

Mercury migrating out of rivers to the shore
Mercury contamination can be a big problem in rivers, as it moves up the food chain accumulating in top predators. But what goes into the river largely stays in the river, or in creatures that feed in it 8212; aquatic insects, fish and fish-eating birds. In the South River in Virginia, however, the mercury has moved from the river to the shore, according to a study by Daniel A. Cristol and colleagues at the College of William and Mary.
They report in Science that some nonaquatic bird species not feeding on fish but that breed within 50 yards of the river have high mercury levels in their blood. The South, a Shenandoah tributary, was heavily contaminated with mercury sulfate from a DuPont factory from 1930 to 1950. Fish and aquatic birds on the river have long been known to be contaminated. But most of the 13 terrestrial birds tested had levels similar to or higher than the aquatic birds. Researchers say the main culprit is spiders, which in some cases make up 30 percent of birds8217; diets and have high levels of mercury. The spiders obtain mercury from their prey, either aquatic insects that are contaminated or terrestrial insects that develop in areas contaminated by flooding.