Archive for the 'Links' category

>AAAS Symposium: The Dynamics of Social Extinction

Feb 19 2007 Published by under Conference Blogging, Conservation, Links, [Politics]

>Following Collins' presentation on amphibians as model organisms for observing biological extinction, Dr. Charles Redman from the Global Institute of Sustainability at ASU addressed a more sticky area of extinction, one that hits closer to home: social extinction.

"The biological extinction of a society is rare," said Redman, describing social extinction as more of a cultural rollover - certain social orders become antiquated and irrelevant and tend to be replaced.

"At some point, the old ways just die out. In some cases," he said, "the language still exists, but the society may not."

Redman questioned the importance of the collapse of societies in reference to the central theme of the AAAS meeting, sustainable science. The loss of a species is unequivocally deemed morally important, but is the loss of society? What causes societies to fail? Is there such a thing as a truly sustainable society?

Redman answered himself simply. "The only thing that is certain is that change is ubiquitous."

He detailed briefly and necessarily the Easter Island paradigm of cultural collapse and the succession of regimes in Mesopotamia as examples, following with a concise definition of societal "resilience," the ability of a society, biologically and culturally, to remain in a desirable state or to be able to change in a desirable way. Redman never exactly defined "desirability," but I think we can assume that state generally involves nonviolent shifts in society.

Redman sees two major threats to a society: environmental changes and the capacity for response in problem solving, either through greater mobility, technology or sweeping social transformations. He pointed out that the simplest and often the most effective response, greater mobility, is no longer feasible. People are generally stuffed into particular nations where travel between is at best, a bureaucratic paper race and at worst, absolutely forbidden. This problem is especially puzzling in this time of globalization, where goods are brought to people across the world. Redman would like to see more people brought to the goods, evening things out a bit more.

I think one of Redman's more poignant statements was "sustainability is not always good" when you're speaking from a societal perspective. The longest lived, strongest governments in human history were not democracies, but totalitarian monarchies and theocracies. Redman questioned the power of democracy to create a lasting, sustainable, resilient society. No answer was implied in the statement; he just wondered if there was potential.

He questioned the value of information to a society, wondering if the availability of information was as much a detriment as a boon, offering too many options, leading to indecision and confusion faced with so many choices. Unlike biological diversity, which is essential in prolonged stabilization in evolved living systems, cultural diversity may lead to gridlock on senate floors, each group holding firm to subcultural principles.

So I'd like to throw a couple of questions that Redman asked out to the blogosphere. Please, spread them around if you would, on your blog, through e-mail, asking friends:

  • When a society is on the verge of extinction, are we morally obligated to save it?
  • Do you agree with Redman about diversity and information in today's society?
  • Is a sustainable, "resilient" society possible? Does in involve greater globalization, as Redman suggests?

I would love to hear your thoughts. It might even be neat to compile a series of responses.

One response so far

>AAAS Symposium: Observing Biological Extinction

Feb 17 2007 Published by under Conference Blogging, Conservation, Ecology, Links, Microbiology

>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 responses so far

>Dinosaurs and the Mystery of Body Temperature III: Intertial Homeothermy

Jan 28 2007 Published by under Animals, Evolution, Links, Paleontology, Physiology

>Body size is an important factor in the debate over whether dinosaurs were cold or warm blooded (or something in between). When you have a land animal 42 feet long weighing nearly as much as a blue whale, temperature models tend to break down. If the dinosaurs were ectotherms, relying on the environment for heat, they may lack the surface area to sufficiently heat the blood pumping directly beneath the skin. If dinosaurs are endotherms, and internally heated by its own metabolism, it may not have enough surface area to expel excess heat from the depths of its massive body.

The following chart shows this principle a little more clearly.


As you can see, the second two cubes have the exact same volume (body size), but the surface areas are vastly different. Large animals like dinosaurs and blue whales are like the middle cube with the smaller ratio; it becomes difficult to use surface area to heat/cool its insides. Also, the more massive an animal is, the more heat it produces/requires, generally speaking.

The reason blue whales get away with being the most massive animal to ever live (so far) is that temperature exchange with their environment is rapid. The ambient temperature of the ocean is on average much lower than ambient temperatures on land, allowing the whale to circulate heat through the thinner parts of its body and allowing the cold water to carry away the excess. Plus, the whale's 100 tons is spread out along 100 feet of body as well.

You can see how a creature on land weighing as much as the blue whale, compacted into 40 or 50 feet and lacking the might present a particular problem for scientists to figure out, especially in the absence of direct evidence.

But, the creature did exist. We're just now picking up the pieces, so to speak.

And recently, scientists put those pieces to good use. By simulating the ontogenetic development of eight different dinos using data from recent bone analyses, they were able to determine that the internal temperature of dinos depended on size. Smaller dinosaurs maintained a lower body temperature and probably grew at a rate consistent with extant reptiles, while the larger dinos maintained a higher body temperature, like today's birds and mammals.

The largest animal studied, Sauroposeidon proteles, was estimated to have an internal temperature of 48 degrees Celsius (120 degrees Fahrenheit), a few degrees higher than what was thought to be the upper limit of temperature tolerance for animals. Because of this extremity, the authors believe that temperature may have been the ultimate cap on body size.

Ultimately, this study was transposing a state called "inertial homeothermy," which is observed in ectotherms like crocodiles and the Galapagos tortoise that can maintain their internal temperatures by adjusting their internal physiological conditions, much like endotherms. The researchers performed the same tests on crocodiles of similar size (when they could; there are no crocs alive today to compare with the larger dinos):


Perhaps, if time allows in the near future, I'll detail a bit more about all the thermies: poikilo, homeo, hetero, ecto and endo.

One response so far

>Dinosaurs and the Mystery of Body Temperature II: The Evolution of Endothermy

Jan 19 2007 Published by under Animals, Birds, Evolution, Links, Paleontology, Physiology

>There's a fairly significant problem with the evolution of endothermy from ectothermy, a paradox that has no satisfactory conclusion as of yet: How could well-insulated animals with high metabolic rates producing lots of heat from within their bodies evolve from animals with low metabolic rates and poor insulation, expertly absorbing heat from the surrounding environment?

If these characteristics evolved independently what purpose would they serve? An ectotherm has no use for insulation like feathers or hair since heat exchange needs to be rapid with its surroundings, just as it has no use for a heat producing high metabolism without the necessary insulation.

Raymond Cowles' experiment showed that by putting little fur coats on lizards wasn't keeping heat in, it was keeping heat out. The lizards couldn't warm up.

That's the paradox, the catch-22. The ticket out, however, is the exaptation: An adaptation of a structure that becomes useful for one biological purpose that originally evolved for another.

Feathers are are thought to be derived from the long scales of ancient archosaurs. These reptiles could lift their scales and expose their skin directly to the source of heat, or orient them so that they could block heat absorption. Just as the marine iguanas of the Galapagos Islands are able to trap a layer of air within their scales, these reptiles are thought to have done the same, retaining more metabolic heat, leading to a more active life.

Another theory concentrates on our reptilian ancestors from the synapsid lineage. The synapsids were steadily becoming more active (illustrated by changes in bone structure), and those morphological changes could have been accompanied by higher metabolic rates, leading to more heat in the body. The more hair on the body, the better heat retention.

So which came first, the dino or the egg?

It's apparent that endothermy evolved at least twice; once beginning with an exaptational insulator in the case of birds, and once beginning with exaptational skeletal changes and a needed increase in activity for foraging, in the case of mammals.

Largely, however, the jury is still out. (I heard that there is also evidence that pterosaurs might have been endothermic, leading to a third origin of endothermy; please link research if you know of any.)

Its important to realize that there are in-between states of thermoregulation, and the progression from ectothermy to endothermy (and back again, in some cases) took place in baby steps across millennia. Time and again we're shown that organisms tend not to fit our definitions and molds. It's not like flipping a switch.

More on dinos and thermoregulation for part III.

One response so far

>Dinosaurs and the Mystery of Body Temperature I: Endothermy vs. Ectothermy

Jan 19 2007 Published by under Evolution, Links, Paleontology, Physiology

>This is repost from September of '06. I never had the chance to finish the series because of school, so I will be finishing in three parts this week.

Why have the dinosaurs been relegated to little kid stuff? Why can't I find a purple triceratops t-shirt in XL?

Were the dinosaurs warm-blooded or cold?

I want to talk about dinosaurs and body temp for a couple of posts, but I think the best place to start is with a little discussion of why this issue is important and the evolutionary implications of endothermal/ectothermal states.

Ectothermy is the state of commonly referred to as "cold-bloodedness" (an inaccurate term; it's more about precise regulation) which is observed in most reptiles (though not all), most fish (not all) and basically every animal that is not a bird or a mammal (though not all). Ectotherms rely on heat from outside sources to maintain their body temperature. The sun is the main source of this heat energy (infrared), which can be transferred directly through absorbing the sun's rays, or indirectly through convection - movement of heat between objects (including organisms) and the air.


When a lizard suns itself, its blood vessels just below the skin open up, allowing more blood to flow next to the skin and the source of heat (the sun's radiation). The lizard's blood warms and transmits heat to the rest of the body.

Endotherms, on the other hands, are animals that regulate their own heat, like us. We don't need external sources because heat production is built in to our metabolic machinery. In fact, most endotherms spend more time trying to dissipate heat than acquire it. As you might expect, there is a formal range of classifications (lower lethal, lower critical, thermoneutral, upper critical, etc.) that biologists can use to determine the tolerances of certain endotherms.

The most important thing to remember is the necessity of temperature regulation in animals, the "why." Metabolism is all about burning calories, and the processes that burn those calories are driven by chemical reactions. Chemical reactions within the body are finicky; they depend on enzymes to catalyze which only work within a relatively narrow band of temperatures.

Endotherms have an advantage in this respect. A constant high body temperature increases the activity of the central nervous system, and subsequently neurotransmitter and enzymatic activity. Ectotherms do not have this advantage; on cool days/nights, they lose the ability to be as active. Keep in mind that this does not mean that endotherms are better, just different.

So what does this have to do with dinosaurs?

The main problem in assessing the body temperature of dinosaurs is that we have no direct evidence. There are no extant dinos, so scientists have to look to their descendents, birds and reptiles. But, as we covered earlier, temperature regulation is far from uniform in these animals.

There is one other problem: temp regulation is a special problem in the case of such huge animals.

Next time we'll look into the evolution of endothermy and how it might have arisen from the dinosaurs.

2 responses so far