Populations of frogs and other amphibians have been declining around the world and biologist Lisa Schloegel believes that she may have discovered why.Schloegel and her fellow researchers concluded that the breeding and farming of bullfrogs in Brazil, Taiwan and China, and the international sales of these live frogs may be spreading a fungus that causes a disease called chytridiomycosis, which is often deadly in amphibians.Although bullfrogs are native to North America part of the natural ecosystem here, their sale, release and multiplication around the world is also creating an invasive species problem in other countries, as the large and aggressive bullfrogs gobble up smaller frogs and amphibians.