In the new analysis, the role of the predatory fish was played by Batrachochytrium dendrobatidis, or Bd, a microscopic fungus that lives in water and moist soil that sickens or kills frogs. Bd is called a chytrid fungus from the Greek chytridium, meaning "little pot" because small blisters filled with sperm-like, flagellated zoospores form in the skin of infected frogs.
Smith thought that the pathogen might be altering the frog communities in the same way the predatory fish had altered the pond communities, causing them to lose both alpha and beta diversity.
People had compared the susceptibility of different species to the fungus but no one had looked for changes in the less appreciated beta diversity.
The baseline assumption of the analysis was that the pathogen was causing no change in beta diversity, the result that would be expected if it hit all species equally as it swept across the region.
Bd is an invasive species whose origin is not known.
The fungus is devastating to frogs because it infects the skin, a much more important organ in amphibians than in other vertebrates. Many frogs breath and drink through their skin and use it as we use our kidneys to maintain the proper concentrations of ions such as sodium and potassium in their bloodstreams. As frogs sicken, their skin peels or sloughs off.
Hoping to find a data set appropriate for the kind of analysis he had in mind, Smith got in touch with Lips, a scientist who has monitored amphibian declines in Central America for many years.
"The basis of this paper is her decades of work in this area," says Smith, "and the astonishing data set they produced."
Lips had species lists from six sites both before and after Bd appeared, and she was able to obtain data from two more sites, for a total of eight.
At her study sites, Lips and her graduate students had walked transects during the day and als
|Contact: Kevin Smith|
Washington University in St. Louis