The alligator has some foreign competition at the top of the Everglades food chain, and the results of the struggle are horror- movie messy. A 13-foot Burmese python recently burst after it apparently tried to swallow a live, six-foot alligator whole, authorities said. The incident has heightened biologists' fears that the nonnative snakes could threaten a host of other animal species in the Everglades. "It means nothing in the Everglades is safe from pythons, a top-down predator," said Frank Mazzotti, a University of Florida wildlife professor. Over the years, many pythons have been abandoned in the Everglades by pet owners....