ARIZONA DAILY STAR (Tucson) 23 January 06 Arizona frog fungus not blamed on warming (Tony Davis)
Tucson, Arizona: Global warming probably isn't triggering the fungal disease killing off Arizona frogs, some Arizona researchers say, despite a new study that concludes warming is causing the extinction of many frog species in Central and South America.
Warming is the underlying cause for the disease killing frogs in Central and South America, but rising temperatures in Arizona are not acting in the same way, two Tucson herpetologists and a State Game and Fish Department biologist in Phoenix agree. Although the chytrid fungus has been a huge problem for Arizona frogs, warming is not a likely cause for it in Arizona because its climate is generally hotter than in Central and South America, say Cecil Schwalbe of the U.S. Geological Survey, Philip Rosen of the University of Arizona, and Michael Sredl of Game and Fish. Paradoxically, the Latin American research says global warming has accelerated chytrid disease there by increasing cloud cover that has cooled daytime temperatures and warmed the nights.
But global warming could threaten Arizona frog species for other reasons, the scientists said. If the state's recent warming trend continues to be accompanied by droughts that have occurred most of this decade, springs, washes and streams that are homes for frogs could dry. That has already occurred in one canyon in Saguaro National Park East, they said. Drying, combined with fires afterward, eliminated a population of lowland leopard frogs early in this decade, Rosen and Schwalbe said.
Even if rainfall stays the same, hotter temperatures will mean increased evaporation that also could dry up the frogs' water sources, researchers said.
"Right now we are in a drought and setting these temperature records. They seem to be hand in hand, although nobody's admitting it," said Schwalbe, an ecologist. "That's why the native frogs are in such trouble. All of these factors acting on the few remaining populations can push them over the edge."
Since 1998, researchers have known that the chytrid fungus is attacking Arizona frogs. They now say it has occurred in 12 Arizona frog species, according to a 2003 Arizona Game and Fish report. About half these species declined significantly because of the disease, while the disease is probably linked to declines in another one-fourth of the species, Rosen said.
On Jan. 12, the journal Nature published a study warning that the chytrid fungus had combined with rising temperatures to drive many species restricted to misty mountainsides to extinction. About two-thirds of more than 110 species of brightly colored harlequin frogs in the American tropics have vanished since the 1980s. Rosen and Sredl, like some other researchers nationwide, expressed skepticism over the conclusions reached by J. Alan Pounds, resident biologist at the Monteverde Cloud Forest Preserve in Costa Rica.
Critics have said there were several layers of remaining uncertainty not eliminated by the analysis. For one, they said it remains unclear whether the lethal fungus, which attacks amphibian skin, has long been in the affected areas and dormant or is a recent arrival. Other researchers have backed Pounds' work.
"In Arizona, die-offs due to chytrids are a wintertime phenomenon. This is a real paradox to any study that links global warming" to the disease, Sredl said. "Global warming, or more correctly global climate change, is not a simple phenomenon. There is no doubt that average global temperatures are increasing. To speculate that this increase in temperature alone will create conditions that will 'benefit' the frog chytrid is premature."
Arizona's climate is so different from the tropics that the Pounds analysis probably doesn't apply at all, Rosen said.
Chytrid fungus and Arizona frogs
Some Arizona frog species probably affected by the chytrid fungus:
- Chiricahua leopard frog, which is listed as a threatened species and lives in Southeast Arizona and in mountains east and south of the Mogollon Rim.
- Tarahumara frog, which disappeared from the state in the early 1980s but was reintroduced in 2004 in a Santa Rita Mountains canyon.
- Northern leopard frog, whose range includes Northeast Arizona.
- Lowland leopard frog, which lives in the Colorado River near Yuma, and Western, Central and Southeast Arizona, south of the Mogollon Rim.
- Ramsey Canyon leopard frog, which lives only in the Huachuca Mountains and may be genetically identical to the Chiricahua leopard frog.
- Plains leopard frog, which lives in the Sulphur Springs Valley.
- Relict leopard frog, which lives in Northwestern Arizona.
- The bullfrog and Rio Grande frog, both introduced species.
Source: Philip Rosen, a University of Arizona assistant research scientist
http://www.azstarnet.com/dailystar/allheadlines/112511.php