For the next 3 weeks, Extinct will be exploring the relationship between paleobiology (and the deep past more generally) and issues in conservation.
Derek Turner writes ...
Picture this: Over a relatively short period of time, huge amounts of CO2 and/or methane get released into the atmosphere. This causes a period of extreme warming that lasts around 200,000 years. Average global temperatures increase by at least 5° C, probably more. There is no ice in the arctic, or anywhere. This might sound like the start of a gloomy forecast, the prophecy of some dystopic future brought about by climate change. But in fact, it’s a description of events that took place between 56 and 55 million years ago, during an episode that Earth scientists refer to as the Paleocene-Eocene Thermal Maximum (PETM). (You can find a helpful overview of what we know about the PETM here.) We don’t know exactly what caused the spike in atmospheric CO2 at that time. But scientists working in the relatively new field of conservation paleobiology think that this moment in prehistory can serve as a model for understanding how nature might respond to human-caused climate change.
Conservation paleobiology challenges some assumptions and stereotypes about historical science. It suggests that the study of prehistory might be both predictive and policy relevant. It can sometimes be helpful to use prehistoric episodes as models for the present. In a recent review of research in conservation paleobiology, Gregory Dietl and Karl Flessa write that “the perspective provided by geohistorical data is essential for the development of successful conservation strategies.”
An important caveat: The Paleocene-Eocene Thermal Maximum is by no means a perfect model for what's going on today. For example, the arrangement of the continents was slightly different 55 mya, and carbon was probably being released into the atmosphere at a much slower rate than today. But no scientific model is perfect in every respect. The interesting question is whether the two episodes might be similar enough, in the right sorts of ways, to help us understand how nature might respond to human-induced changes.
Changing Geographic Ranges on a Warmer Planet
One important question about climate change has to do with biogeography: as average temperatures rise, some species might be able to shift their geographic ranges; others (e.g., those stuck in alpine ecosystems) will have more trouble. Can studying the Paleocene-Eocene Thermal Maximum help us get a clearer sense of how different types of organisms will fare on a warmer planet?
One of my colleagues in the Botany Department at Connecticut College, Peter Siver, works in paleolimnology—the study of prehistoric freshwater lakes and ponds. Siver has looked at core samples taken from the bottoms of ponds in the Canadian arctic. He studies microfossil remains of unicellular siliceous algae—diatoms and chrysophytes. Both are well represented in the fossil record. Diatoms, in particular, have distinctive cell walls made of silica that can be quite beautiful. (He has made some images of diatoms and chrysophytes available online here.) When Siver and a Canadian colleague, Alexander Wolfe, looked at a drill core sample from a site near Yellowknife, Canada, they found diatoms and chrysophytes dating from around 55 million years ago that are morphologically indistinguishable from those living in the tropics today! That result deserves an exclamation point for at least two reasons. First, this is a pretty interesting case of long-term morphological stasis (the topic of an earlier post). But more importantly, this result strongly suggests that the organisms that form the basis of freshwater ecosystems are able to expand their geographic range in response to environmental change. Siver and Wolfe write that “as global climates continue to warm under increased anthropogenic greenhouse-gas forcing, we may predict that warm-water ochrophytes will undergo range expansions”—a lovely example of predictive paleobiology. (“Ochrophytes” is the group that includes both diatoms and chrysophytes.)
Insect Damage to Ancient Forests
Nor is it only microfossils that can teach us how populations might respond to climate change. If you have traveled much in the Rocky Mountains recently, you may have observed the damage done by pine bark beetles, which attack lodgepole and ponderosa pine trees. The beetles are native to the Rockies, where cold winters usually help to keep their numbers down. Warmer winters in recent years have contributed to an outbreak that has devastated forests from New Mexico to British Columbia. This is just one example, but it raises a pressing question: As the planet warms up, what sorts of things can we expect insects to do to trees?
Here again, paleobiologists studying the Paleocene-Eocene Thermal Maximum have something to offer. It turns out that in certain locations, such as the Bighorn Basin in Wyoming, the plant fossil record from the crucial time around 56-55 million years ago is quite good. In one recent study, a team of scientists looked at over 5,000 fossil leaves from five sites in Wyoming. A great many of these fossils display evidence of damage from hungry insects. (Check out the full text of the paper, along with images of fossil leaves with insect damage.) So the scientists came up with a system for classifying 50 different “insect feeding morphotypes”—which is to say, 50 different kinds of leaf damage. They found that both the overall amount of insect damage and the diversity of damage spiked coincidentally with the extreme warm spell right at the end of the Paleocene. The paper concludes with an ominous prediction: “The dramatic rise in diversity and frequency of herbivore attack on all abundant plant species during the PETM suggests that anthropogenic influence on atmosphere and climate will eventually have similar consequences.”
These examples show how paleobiology can yield results that might help inform conservation efforts as we try to figure out how to protect biodiversity on a warming planet. But they also point to an interesting philosophical lesson about modeling in historical science.
Past-directed vs. Past-sourced Modeling
Paleontologists routinely use present systems as models for understanding the past. For example, I once met an experimental taphonomist (someone who studies fossilization processes) whose research involved tossing animal bones—I think mostly from sheep—into a stream. Then he would return months later to see what the stream had done to them: how far had it carried them, and where were they deposited? The idea was to use the present experimental system as a model to help with interpreting fossil remains from the deep past. Those of us philosophers of science who like to think about historical reconstruction have had a lot to say about the ins and outs of this sort of modeling. Let’s call it past-directed modeling. It’s important, though, to avoid the mistake of thinking that past-directed modeling is the only kind that paleontologists do. The examples I’ve related here would be better described as past-sourced modeling. In these cases, the present situation is the target system, and prehistory is the source of models that help us understand the present and project trends into the future.
F.A. McInerny and S.L. Wing (2011), “The Paleocene-Eocene Thermal Maximum: A Perturbation of Carbon Cycle, Climate, and Biosphere with Implications for the Future,” Annual Review of Earth and Planetary Sciences 39: 489-516.
 G.P. Dietl and K.W. Flessa (2011), “Conservation paleobiology: putting the dead to work,” Trends in Ecology and Evolution 26(1): 30-37.
 P.A. Siver and A.P. Wolfe (2009), “Tropical ochrophyte algae from the Eocene of northern Canada: A biogeographic response to past global warming,” Palaios 24(3): 192-198.
 E.D. Currano, P. WIlf, S.L. Wing, C.C. Labandeira, E.C. Lovelock, and D.L. Royer (2008), “Sharply increased insect herbivory during the Paleocene-Eocene Thermal Maximum,” PNAS 105(6): 1960-1964.