By Jon Christensen
So this is what it feels like to be in the throes of a paradigm shift. It turns out that much of what we think we know about species and ecosystems is wrong.
That’s a strong word: wrong. But it’s the word that James H. Brown uses to describe the current state of biogeography, the study of the distribution of species and ecosystems on Earth, a science at the heart of conservation.
“Much current biogeographic theory is either wrong, too simplistic, or relevant to only specific instances,” Brown told the inaugural meeting of the International Biogeographic Society two years ago, and he’s been talking about it ever since.
And Brown would know. A professor of biology at the University of New Mexico, Brown has had a distinguished career recognized with top awards from his peers in the Ecological Society of America. He has come at biogeography from both ends. His research has been nose-to-the-ground in a long-term experimental study of a small patch of Chihuahaun Desert to tease out microscale ecological relationships. And it has been head-in-the-clouds theoretical research in biological scaling and macroecology, crunching massive databases in search of the universal patterns of biodiversity.
When Brown talks about biogeographic theory, he’s not talking about something irrelevant to conservation. He’s talking about the basic rules that seem to explain either the survival or extinction of species, the resilience or unraveling of ecosystems.
A year ago, in Frontiers of Biogeography, Brown presented seven assertions that challenge current theory and are based on recent research.
1. Species diversity of most taxa inhabiting islands and insular habitats is far from a dynamic equilibrium between opposing rates of colonization and extinction.
2. Much, perhaps most, speciation is not allopatric.
3. Different taxonomic groups living together in the same place usually do not have congruent biogeographic histories.
4. Range shifts in response to major geological and environmental changes have not been unidirectional and coincident across different species, lineages, and functional groups.
5. Diversity of most lineages cannot be explained simply by a difference between speciation and extinction rates.
6. Latitudinal and elevational patterns of diversity are often different.
7. The current rate and magnitude of human-caused global extinctions are not the greatest in Earth history.
Now, a few of these points are more arcane than others. And there may be those who wonder why we should care about theory in a world crying out for practical conservation. The reason is that these are the theoretical underpinnings of much practical conservation of island-like habitats of diverse species in a changing world. If we get the theory wrong, all of the predictions we make and actions we take also stand a good chance of being wrong.
Brown and other biogeographers have been saying all of this in professional circles for a few years now, but the word hasn’t really gotten out to the broader conservation community. Why? That seems to be the nature of paradigm shifts. Even as the support for current paradigms is undermined to the point where the entire edifice is about to collapse, most conservationists soldier on, doing the best they can with the theories they’ve got. Not Brown. He wants the debate to begin now, before it’s too late.
Jon Christensen is a research fellow in the Center for Environmental Science and Policy at Stanford University.
The Uneasy Chair is named in honor of Bernard DeVoto, who, from 1935 to 1955 wrote “The Editor’s Easy Chair” column for Harper’s magazine-a perch from which he often sallied forth in defense of conservation. Wallace Stegner’s biography of DeVoto was more aptly titled The Uneasy Chair (Doubleday, 1974), from which this column takes its name and its challenge.
