Avoiding Mass Extinction: Basic and Applied Challenges
Rosenzweig, Michael L., The American Midland Naturalist
Preserving the earth's diversity of species requires that conservation biology turn much of its attention to reconciliation ecology, which is the science of sharing our habitats with wild things. Although many reconciliation projects are already working, we can extend our efforts with modern natural history research focused on species we aim to open our landscapes to. Some of this research will utilize what we already know about the principles of community ecology and niche organization and some will teach us more about those subjects. Perhaps most important will be a deeper understanding of the coevolution of niche apportionment. However, lacking perfect understanding is no reason to delay. The ecologist's motto ought to be, "Stop whining and try something."
What produces and controls the number of species? Perhaps that is the classic ecological question. Ecology and evolution have devoted themselves rather continuously and assiduously to it for two centuries (von Humboldt, 1807; thru Darwin, 1859; Wallace, 1876; Dobzhansky, 1941; Simpson, 1944; Mayr, 1963; MacArthur, 1972; Rosenzweig, 1995 and beyond). What an intellectual prize for us all! It is just as exciting to contemplate as our victory if cosmology were at last to succeed in discovering the true history of the physical universe and the mechanisms that produced it.
We practice cosmology largely to satisfy our curiosity. Understanding diversity also has that value. However, it has inestimable practical value as well. What people have done to the land and the waters of this planet threatens it with a great mass extinction, one comparable to only a handful in its entire history. I suspect no one wishes an anthropogenic mass extinction. But if we are to prevent one, we surely must understand what regulates species diversity and how these processes result in its reaching a sustainable level in nature.
Increasingly, the footprint of Man marks the landscape with the enterprises of civilization. Homo sapiens dominates the Earth. We use nearly half of terrestrial primary production. We more than double the global cycling of nitrogen (Vitousek et al., 1997). Some ecologists estimate that we may have expropriated 'only' about 40% of the terrestrial surface of the Earth (Vitousek et al., 1997), others say as much as 95% (Huston, 1993). I actually see the hand of Man everywhere, changing climates, depleting ozone, growing food, wood and fiber, extracting water and minerals. Perhaps none of this is intrinsically threatening to diversity, but it does place a high priority on developing tactics that integrate conservation with human needs.
Our task is epic and dramatic, monumental and clear. People have already engineered the Earth's habitats. The time has come to learn how to do that without endangering most of the world's species. Then we must merely re-engineer the entire Earth, but this time, responsibly.
I believe we can do it and I will explain why.
BASIC PROCESSES THAT DETERMINE SPECIES DIVERSITY-SCALE MATTERS
As all ecologists and evolutionists know, species come and species go. The difference between the rates at which they come and go determines the rate at which diversity changes. Sounds simple, but it is not.
What complicates matters is the question of scale. The dominating processes of origination and extinction depend on the scale of space and time we choose to study (Rosenzweig, 1999).
At the evolutionary time scale, the advent of a species is called speciation. Its disappearance is a global extinction. Often these processes occur at a glacial pace. Species tend to come and go at time scales of 10^sup 5^ to 10^sup 6^ y. An area whose dominating processes of diversity change are speciation and global extinction is called a biogeographical province (Rosenzweig, 1995).
Islands work faster, i.e., at time scales of 10-10^sup 4^ y. At the island time scale, species arrive by immigration from somewhere else. …