Conservation Paleobiology

By Karl W. Flessa

(excerpt from American Paleontologist, vol. 10, Number 1, p. 2-5.)

Deciphering the biology of once-living organisms isn't just fun, it can be important fun. There is a new applied side to our discipline, an application that I call "conservation paleobiology", Conservation biology is the science that examines the human impact on biological diversity and develops practical approaches to the prevention of species extinction. Conservation paleobiology is the application of paleoecological and geochemical techniques to the analysis of the prehistoric and historic skeletal remains of species threatened with extinction.

Understanding the biology of endangered species is difficult for many reasons. The most obvious reason is that they are rare: individuals may be hard to find and population sizes may be so small that direct experimentation or even observation could have an effect on the species' survival. In addition, the original range of the species may have contracted so much that its present habitat may be neither typical nor ideal. Species now known only in zoos are examples of species whose ranges have undergone extreme contraction.

So the problem is to find an approach that doesn't interfere with living individuals and can be used to examine them under natural conditions - before the species was affected by human activity.

The approaches and techniques of paleontology meet these criteria nicely. Hard part skeletal remains can be found in natural accumulations such as reefs, shell beds, cave deposits, lake sediments and packrat middens. Vertebrate, invertebrate and plant remains can also be recovered from kitchen middens and other archeological sites. Museums often house valuable collections of animals and plants- collections made decades to centuries before large-scale, human-caused changes in habitat.

Of course, the remains of once-living organisms are not the only source of information. Publications, ranging from the notes of early explorers to formal biotic surveys are often important sources of information about the distribution, abundance, and biology of now-threatened species.

A wonderful example of conservation paleobiology in action are the efforts to establish a population of the California Condor in the Vermillion Cliffs area of northern Arizona. This reintroduction of the species was guided by knowledge that the California Condor once occurred in the area - as documented by the bird's skeletal remains in late Pleistocene cave deposits.

There's another frequent problem in conservation biology that can be addressed through the analysis of prehistoric or historic biotic remains. In many circumstances, human activity started affecting natural habitats before any systematic observations were made of those habitats. How can we know what the effect of some human activity has been if we don't know what conditions were like before that activity began? How can we make a "before and after' comparison when we don't know what "before" looked like?

The closely-related discipline of historical ecology addresses these sorts of issues and frequently employs paleontological techniques to construct reference conditions for assessments of environmental impact and goals for ecological restoration. For example, ecologists and paleoecologists have recently used a variety of "retrospective data" (historical, archeological, ecological and paleoecological records) to argue that overfishing since colonization by Europeans caused the collapse of North American coastal ecosystems (Jackson et al., 2001, Science 293: 629-638).

Looking back in time is essential for such purposes. Certainly one of the lessons of the record of life on Earth is that environmental conditions never remain constant for very long. Even short-term climatic fluctuations - especially within the late Cenozoic - can have significant effects on the composition and distribution of biotas.

So a search for a single "baseline", an environmental benchmark of pre-human conditions, is likely to be both frustrating and useless. Should our baseline for conditions in North America be 1491 - the year before Columbus arrived? Or should it be sometime in the late Pleistocene - before the arrival of the ancestors of Native Americans?

Instead of finding a single set of reference conditions to evaluate the subsequent effects of human activity, it makes more sense to use the historic or prehistoric record to estimate the natural range of variability in environmental conditions. If this can be done with some rigor, then a stronger case can be made for human impact if current conditions are demonstrably beyond the range of natural variability.

The record of the past is important for yet another reason. Some natural events and conditions are so rare that they have not been witnessed within human history. For example, asteroid impacts, warm polar regions and stagnant oceans don't lend themselves to direct study today. The only way to find out how biotas react to such conditions is to look to the fossil record.

We employ conservation paleobiology to examine the effects of freshwater diversion on the Colorado River Delta and to provide target parameters for its restoration. See a recent summary of our work here.