© Tim Springer
Good-bye Wolf, Hello Coyote
It's a decline heard round the world. Top-of-the-food-chain predators such as wolves, cougars, lions and sharks are disappearing. Silently, smaller "mesopredators" such as coyotes, baboons and rays have stepped in to take their place, causing a new set of problems.
"This issue is very complex and a lot of the consequences are not known," says William Ripple, a professor at Oregon State University who, along with researchers from University of California-Berkeley and New Mexico State University, authored a recent study on the phenomenon, published in the October issue of BioScience. "But there's evidence that the explosion of mesopredator populations is very severe and has both ecological and economic repercussions."
In fact, the disruptions caused by the absence of the "top dogs" may dwarf any problems presented by the original large predators, say the researchers.
Take wolves in the northern Rocky Mountains, for example, which have been killed to appease ranchers who fear attacks on their livestock. The absence of wolves has led to a surge in numbers of coyotes, a smaller predator once kept in check by wolves.
Livestock losses from coyotes are beginning to mount. For example, coyotes killed 5,700 sheep and lambs in Oregon in 2004, where wolves were wiped out by the 1940s. By comparison, mountain lions killed 1,200. Attempts to control coyotes have cost hundreds of millions of dollars.
"The wolves are gone in many places and coyotes are killing thousands of sheep all over the West," says Ripple. Compounding matters, mesopredators naturally occur at higher densities and are more adaptable than top predators. This means they'll be even harder to control, he adds.
Similar scenarios have played out elsewhere in the world. In Africa, where lion and leopard populations have been decimated, populations of crop-raiding baboons have exploded. And the problem is not confined to land. With sharks imperiled from overfishing, some places have seen huge increases in rays. These smaller predators are expanding their range in search of scallops and harming the fishery.
The researchers expect the economic impacts of these smaller predators will exceed those of the apex predators. And in some cases, the cost of controlling mesopredators is so high it would be cheaper and more effective to return the top predators back into the ecosystem.
In other words: More wolves in the West could actually mean more sheep.
Playing it Cool
"Follow my nose, it always knows," says Toucan Sam, the famous Kellogg's Froot Loops cereal mascot.
Researchers, however, don't know the real purpose of the toucan's bill, largest of any bird's relative to body size. Charles Darwin thought it was to attract mates. Other researchers have suggested its length makes it perfect for fruit-picking in trees.
Now there's another theory: It serves to keep the bird's body at a comfortable temperature, much like a car's radiator, says Glenn Tattersall, a biologist from Brock University in Ontario. Using an infrared camera to measure heat flow from the bill, he tested his theory by chasing a toucan around a cage for 10 minutes. Voila! The bill heated up, helping the bird to stay cool.
But does this mean that the bill actually evolved for this purpose? No one really knows.
A Heart-Stopping Discovery
Scientists have found the croaking gun in the case of the fatal fungus felling frogs worldwide: the mechanism by which it kills.
The highly contagious fungus, Batrachochytrium dendrobatidis (Bd for short), causes chytridiomycosis, the skin disease linked to the decline or disappearance of as many as 200 species of frogs in recent years. But how Bd kills has remained a mystery, because its victims appear healthy except for superficial skin lesions.
To crack the case, a group of scientists led by Jamie Voyles of James Cook University in Australia conducted a series of experiments with infected green tree frogs. They discovered that Bd impairs the flow of sodium, chloride and other crucial electrolytes across the amphibians' skin, ultimately leading to heart failure.
More research is needed to determine exactly how Bd disrupts skin function and electrolyte transport. But hopes are high that these findings will lead to the development of new methods to save endangered amphibian populations and halt the frog march to extinction.
Bears on Wheels
It's the stereotypical choice of suburban moms all over the country. But the minivan has another fan: black bears.
Bears at Yosemite National Park have figured out that minivans offer the best opportunity for sating their appetites, according to a seven-year study by the U.S. Department of Agricultural National Wildlife Research Center and Yosemite National Park. From 2001 to 2007, minivans had the largest number of break-ins by bears. Of the 908 reports of vehicles broken into by Yosemite black bears, 26 percent were minivans—even though they made up only 7 percent of the vehicles parked overnight.
The researchers say minivans carting children—who are more prone to spill food—might be more likely to emit enticing odors. It's also possible minivans carry more coolers and grocery-filled bags—although visitors are educated to use food storage lockers and not to leave food in their vehicles overnight. The vans may also be easier for the bears to get inside—most animals gained access by popping open a rear side window.
Whatever the reason, one thing is certain: Bears are adept at adapting to us when it comes to filling their own tanks. And that's more food for thought for us, as we try to figure out how people and carnivores can coexist peacefully.
Consumption of the Conspicuous
When rising ocean temperatures bleach coral and leave reefs looking like unfinished paint-by-number pictures, what happens to the colorful little reef fish that used to blend into the background to evade predators? They become dinner.
Researchers at Australia's James Cook University placed two species of damselfish, one briliant yellow, the other bold black-and-white stripes, in tanks filled with coral in various conditions from healthy to long-dead. They then introduced a predatory reef fish, the dottyback, into the tanks.
Not surprisingly, the damselfish in the tanks with healthy coral fared the best, losing only 25 percent of their numbers. As the condition of the coral deteriorated, it increasingly became a case of damselfish in distress. Predation of the brightly colored prey fish rose as high as 42 percent in tanks with dead, algae-covered coral.
"These results suggest that coral-dwelling fishes are much more conspicuous against the bleached-white background, increasing their susceptibility to predation and contributing to declines in abundance of coral-dwelling fishes after host coral bleaching," says chief investigator Darren Coker. Even if the fish don't die, says Coker, "increased exposure to predators is likely to provide significant motivation for coral-dwelling fishes to vacate bleached coral," leaving nothing but a blank canvas where a vibrant and biologically diverse scene used to be.