February 17, 2007

AAAS Symposium: Observing Biological Extinction

The first symposium I attended was yesterday at 8:30 am entitled "The Dynamics of Extinction," which was organized to be an interdisciplinary approach to examining extinctions in natural, societal and lingual systems, and also the ethics involved in preserving - and perhaps necessarily - intervening in these systems.

Ecologist Jim Collins of the NSF and Arizona State University kicked off the discussion with an analysis of global amphibian decline as an indicator of extinction, and also a type of living experiment. It is usually the job of paleontologists to analyze fossil and climate records, correlating extinctions with major environmental change.

"At this moment, however," said Collins. "Extinction is right in front of us. We actually get to peer through the window this time."

And amphibians are the perfect example, a model class, said Collins. It's easy to see why. Thirty-three percent of amphibians are endangered, with 7.4 percent of those considered critically so, compared with 23/3.8 percent of all mammals and 12/1.8 percent of all birds. It is striking that we're talking about an entire class of animals that are being pushed to the brink, not just a particular family or genus.

Collins listed the different threats that may lead to extinction in these animals, including the "historic" threats,
  • Commercial
  • Introduced species
  • Habitat reduction
as well as some newer, less studied threats, labeled "enigmatic":
  • Climate change
  • Toxins
  • Infectious agents
The enigmatic threats became more prominent as biologists noticed declining amphibians populations even within protected lands. Since the enigmatic threats are not subject to arbitrary human boundaries, they persist even when an area is isolated from the first three historical threats.

But commercial harvesting is still a major threat for amphibians, especially frogs. The frog leg industry is especially destructive, concentrating their harvests on only 11 species of frogs, 95 percent of the time harvested from natural habitats, not farms.

Toxins are hard to label as a concrete cause of because of the stratified and highly variable distribution of contaminants in biological systems, especially those bound to aquatic environments. Collins suggested that the deformities caused by parasites in frogs may be due indirectly to an increase in fertilizers, though that idea has not been confirmed.

Collins instead concentrated on his own work with Central American frog populations and the potential for a type of fungus, Chytrid to extinguish about 100 species of frogs in the area. Chytrid attacks the kerotin-rich skin of the frog, and since these animals respirate through their skin, advanced cases cause cardiac arrest and death. Chytrid has also been known to disrupt normal behaviors in frogs.

The idea of a pathogen driving its host to extinction seems contradictory; where's the benefit for the pathogen?

There are a few species of Chytrid resistant frogs in these communities that act as a reservoir species for the fungus. In other words, these frogs show no symptoms of infection, but still maintain the ability to spread the disease (a kind of Typhoid Mary). It's easy to see how this might cause a large extinction of frogs from the constant exchange of Chytrid between susceptible and resistant species.

And the whole bit might be caused by climate change, at least on the local level. As the microclimate shifts, certain pathogens seem to spread more effectively (as in the case of avian malaria in Hawaiian birds).

Collins and company were also able to predict the spread of the fungus to the next location south, more or less confirming the climatic/pathogenic threat of extinction. He has shipped over 100 different species of the most endangered frogs to a zoo in New York (not sure if it was Brooklyn or not) to try to protect and preserve them.

The question is, does this count? If the animal only exists in a zoo, are we truly preserving diversity? More questions were raised in the ethical implications of extinction: When should we intervene? How do we know when the cause of endangerment is natural or artificial? How to define was is natural or artificial?

Collins urged the philosophers of science to step up and engage questions like these, weighing the importance of value systems in ecology, intrinsic value vs. utilitarian value. He feels that we need a more clear philosophy of what should be preserved and how, all the while keeping in mind what exactly our role is in this process.

Back later with more tidbits from this symposium.

2 comments:

  1. Neat stuff. Just one correction: chytrids are phylum of fungi, not a genus. The particular species killing amphibians is Batrachochytrium dendrobatidis.

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  2. Correction noted, Jane. Don't really know why I italicized...

    Zzz...

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