Inside Science News Briefs

A collection of brief stories from the world of science

By Jim Dawson
Inside Science News Service
October 20, 2008

For Want of a Tadpole

What happens to the ecosystem of a stream when all of the frogs die and tadpoles (baby frogs) no longer swim through the water? A killer fungus that is decimating amphibian populations worldwide has given researchers at the University of Georgia an unfortunate opportunity to answer that question, and they found that tadpoles play a key role in keeping the algae at the base of the food chain productive. Without the algae, they discovered, bad things happen. "Many things that live in the steam depend on algae as a base food resource," said Scott Connelly, a doctoral student in ecology whose research appeared in the journal Ecosystems. "And we found that the system was more productive when the tadpoles were there." The research reveals the interconnectedness of ecological systems and how even seemingly trivial changes can cascade through the systems. In 2003 Connelly and a team of researchers set up study sites at two streams in Panama. One site had already suffered a catastrophic loss of frogs due to an invasion of the chytrid fungus. Frogs at the other stream were healthy, but in the path of the fungus disease. Experiments on the two sites indicated that, through a series of interactions, streams without tadpoles swimming along the streambed experience a 150 percent increase in sediment, blocking the sunlight the algae needed to grow. In 2004 the fungus hit the healthy frog population, and when the massive die-off began, the changes to the stream were even greater than scientists expected. Populations of other creatures that depended on the algae declined, as did populations that depended on the frogs - such as snakes. "We predicted the direction of the change, but underestimated its magnitude," said ecologist Catherine Pringle. "Once the frogs die, it's like an incredible silence descends over the whole area. It's eerie." Scientists can save individual frogs infected with the fungus, but haven't found a fungicide that works in an entire watershed.

The Stalagmite Warning

In early December, 1990, schools and businesses in four states near the New Madrid region of Missouri shut their doors in fear after Iben Browning, a retired biologist, predicted there was a 50-50 change of a magnitude 6.5 earthquake along the New Madrid fault. He based his prediction on tidal forces - the alignment of the Earth, Moon and Sun. That earthquake didn't happen, but the fear was based in the region's history. Four significant earthquakes struck the area between 1811 and 1812. One of the quakes, a magnitude 8.0, reportedly caused the Mississippi River to momentarily reverse course. Earthquakes of the 2.0 to 5.0 variety remain common in the area. Now researchers working with the Illinois State Geological Survey and the University of Illinois have found an unexpected way not only to trace the history of earthquakes in what is known as the New Madrid Seismic Zone (NMSZ), but to perhaps predict when the next big one will strike. Keith Hackley, an isotope geochemist with the geological survey, said that because the NMSZ is beneath so much sediment, tracing its past movements have proven difficult. Typically the faults can only be found by searching for rare "sand blows" and "liquefaction features," small mounds of liquefied sand that squirt to the surface through fractures during earthquakes. It occurred to the researchers that the stalagmites that rise from the floors of the caves found throughout the region might hold the key to NMSZ's earthquake history. Using dating techniques on stalagmites from two caves in southwestern Illinois, the researchers discovered that some of them began to form just at the time of the 1811-12 quakes. Stalagmites form when water trickles through crevices in the ceiling of a cave and drips onto the floor, building up a pillar of calcium carbonate. When large earthquakes occur, old cracks may seal and new ones open, leading to the formation of new stalagmites. By drilling into the stalagmites, the researchers have found evidence of seven historic earthquakes dating back as far as 18,000 years. By using the stalagmites to fill in the history of quakes, the researchers hope to discern whether there is a regular pattern to the major quakes in the zone, a pattern that can predict future quakes.

A Dinosaur Dance Floor

In the midst of a Sahara-like desert 190 million years ago in what is now the Southwest U.S., there was a water hole that apparently was very popular with lots of dinosaurs. University of Utah geologists have identified at least a thousand dinosaur footprints - and perhaps thousands more - in a wilderness area located within the Vermillion Cliffs National Monument on the Arizona-Utah border. The three-quarter-acre site, called both the "trample surface" and the "dinosaur dance floor" by geologists working the site, has been known for sometime, but those who had seen the remote site though the tracks were just potholes formed by erosion. Marjorie Chan, chair of geology and geophysics at the University of Utah, first visited the site in 2005 with a Bureau of Land Management ranger who was curious about the "potholes." Chan first identified them as potholes, but their high concentration in just one area was inconsistent with what one would expect with pits caused by weathering. In 2006 her colleague, Winston Seiler, visited the site and, "within about five minutes of wandering around, I realized these were dinosaur footprints." The area is thought to have been a watering hole, perhaps one in a network of watering holes, in the vast desert that covered the area during the Early Jurassic Period. Seiler said the tracks indicate there were at lease four dinosaur species that used the waterhole, including adults and their young. "The different size tracks [1 inch to 20 inches long] may tell us that we are seeing mothers walking around with babies," he said. The researchers also found what they believe are the marks left by dinosaurs dragging their tails. "It was a place that attracted a crowd, kind of like a dance floor," Chan said. The research was published in the international paleontology journal Palaios.

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