Hybrid "Superpredator" Invading California Ponds

Christine Dell'Amore
National Geographic News
June 29, 2009

Mating between the rare California tiger salamander and the introduced barred tiger salamander has created a monster—at least for animals that dwell in the ponds of California's Salinas River Valley. (See a map of the region.)

The new hybrid "superpredator" grows larger than either of its parent species, and its bigger mouth enables it to suck up a wide variety of amphibian prey, said lead study author Maureen Ryan, of the Center for Population Biology at the University of California, Davis.

Mostly on the menu are smaller pond species, such as the Pacific chorus frog and the California newt—both of which were "dramatically reduced" in population by the hybrid in the experiments.

This may be the case in natural ponds as well, Ryan said.

"[The hybrids] seem to be more voracious and a little more aggressive," Ryan said. "Just watching their behavior, they'll go after each other and the other prey."

Cannibal Ambush

Barred tiger salamanders were introduced to California in the 1940s and '50s from Texas.

Hybrids of the invaders and native salamanders now occupy about 20 percent of the indigenous amphibian's range in the Salinas Valley.

The native California species is listed as endangered in Sonoma and Barbara Counties and threatened in the rest of its range under the U.S. Endangered Species Act.

(Related: "Interspecies Sex: Evolution's Hidden Secret?")

To find out how the hybrid is impacting local ponds, Ryan collected tadpoles (juvenile frogs), larvae (juvenile salamanders) and eggs from various species from various sites within the valley and observed them in outdoor experimental ponds.

She and her team found that the hybrid larvae not only ate other amphibians, they also preyed on the native species' larvae.

Continued on Next Page >>




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