Extinction linked with climate changes:post from VL

[NicoleRussell]

There is no longer a true herpetology forum anymore so I thought I would send this out to the venom group. The fact that the frogs may be dying from a toxin from the fungus is a stretch but I thought many of you would be interested in this topic anyway.


Hello all,
You all have heard about the Nature paper associating Global Climate change with a large number of extinctions in Atelopus species because of the optimal growth temperatures of the chytridimycosis fungus. As I read this paper I realized one major flaw in its reasoning. If temperatures that have been recorded since 1988 or so have also occurred in the recent past, then these frogs should have gone extinct a long time ago if warmer global temperatures causes increases in fungal growth and thus infect frogs more easily is the primary mechanism for their extinctions.

The latest time period when the temperatures were as warm as they are today or warmer was in a period called the Holocene Climatic Optimum, about 5-8 k YBP. The average global temperatures were 0.5-2 C warmer than today and lasted for several thousand years. Even if these temperatures are now too warm for optimal fungal growth one would expect that at some point the temperatures would have been as optimal as they are today resulting in the same pattern of fungal growth.
I think the explanation in this article is too simplistic. There have been several papers suggesting that herpetologists and/or ecotourists have spread the fungus to pristine sites. Perhaps what is happening is a combined impact of the spread of the fungus and increasing temperatures. In all probability the real reason is likely more complex than even this simple explanation.

Below are a few quotes I obtained from the web regarding the Holocene Climatic optimum. There is a lot of material out there on this subject I am not trying to be comprehensive here - just illustrating this time period with examples.

James Ball
jamescball@rc.net
313 845 0634


For Pacific Islands, the period AD 750 to 1300 was a climatic optimum marked by warm temperature, high sea level, and probable aridity (Nunn and Britton 2001; Nunn 2003). This was the period of long-distance Polynesian migrations and colonization across vast oceanic distances. The Pacific climatic optimum during the 12th century is confirmed by tree-ring records of the Huon pine from Tasmania (Cook et al. 1991).

The warming resumed by 8500 BC. By 5000 to 3000 BC average global temperatures reached their maximum level during the Holocene and were 1 to 2° Celsius warmer than they are today.

Climatic Optimum
Warmest period during the Holocene epoch. This period is dated from about 5,000 to 3,000 BC. During this time average global temperatures were 1 to 2° Celsius warmer than they are today.