Gary Belovsky <> Eugene Cittadino <> John Haught <> Larry Rasmussen <> Elspeth Whitney

Stuart Pimm

From the "Balance of Nature" to the "Flux of Nature"
Abstract

     Since the time of Darwin, there has been tension between the religious and scientific communities. Be a scientist in the wrong place - such as the United States - and at the wrong time - any time in the last century - and there is an ever-present threat of legislation being enacted that would terminate one's career. Some states have implemented such statutes, while others have failed by slim margins. Without wishing to add to the voluminous literature on this battleground, some points warrant attention.
     First, both sides expend considerable resources to ensure victory. Less obvious are vital efforts at reconciliation. The result is a stalemate, with no perceptible change in the attitude of many voters in a century or more. Second, those scientists targeted for special attention are generally those concerned with the variety of life on Earth, for at issue is how that variety arose. (Certainly, geologists and astronomers are in the cross hairs, too.) Third, and based almost entirely on my own personal experiences, is that those with religious or deep ethical concerns seem to suffer particular abuse. (Given the long, bloody history of inter-denominational conflict, it would be surprising if it were otherwise.)
This is a most unfortunate backdrop to the issue at hand: Not how the variety of life arose, but how fast it is disappearing. Most of us who study that subject came to it from a background of "evolutionary ecology" - the birth of species as it were. Study such a subject even superficially and it becomes immediately obvious that the variety of life is shrinking rapidly. Studying - and preventing - this unnatural death of species becomes an inescapable career shift, particularly for those who have "religious or deep ethical concerns." While there are well-founded economical arguments for saving life's variety, few believe humanity can apply them to every circumstance or with sufficient urgency. The loss of species is fundamentally an ethical issue.
     The scientific position asks: Is there anything special about the present, compared to half a billion years of change? Haven't species always gone extinct? The dinosaurs, at least, are no longer with us; their resurrection in the movies tells us they were many and varied. Isn't Nature always in flux? Isn't humanity an integral part of all natural ecosystems, so denying attempts to separate us from them?
The scientific consensus is that human impacts are driving species to extinction hundreds to thousands of times faster than expected from the natural background rate. An equivalent question to ask is: How often has life disappeared at the rate we project? Only five times in life's history is the answer: This is the Sixth Extinction. And it was the last comparable event, 60 million years ago, that eliminated the dinosaurs. This perspective allows a follow up: How long did it take life to recover after previous mass extinctions? The answer is roughly ten million years.
     Critics challenge this consensus. Perhaps giving them more credit than they deserve, I examine four concerns. First, that the extinction crisis is not real. It is and high rates of extinction are the rule, not the exception. The second criticism dismisses the problem as one restricted just to islands. ("The dodo went extinct" - as the Oxford English Dictionary puts it, suggesting the dodo was responsible for its own demise.) Island species have special vulnerabilities, but they are far more locally abundant within their ranges than are continental species with the same range size. There are large numbers of locally-rare, continental species with small geographic ranges that are threatened by human impacts.
     A third criticism argues that there have been too few species go extinct following the clearing of forests. The favoured case history is eastern North America and critics argue that it casts doubt upon the relationship between habitat loss and species loss. Analysis of this case history shows that exactly as many species of birds were lost as expected. The region had very few species to lose. Extensions to species-rich areas confirm the expected calibrations with an interesting caveat. Forest losses predict the number of threatened species - those on the verge of extinction - not the number of extinctions. This leads to the final criticism: that there have been too few recent extinctions. The reply is that species do not go extinct immediately; some doomed species can linger for decades. More than 10% of species are already in serious trouble.
     While I can contemplate battling another century over how species are born, we do not have that long for species' deaths. Perhaps we do not need to do so. The scientific position is that there is nothing normal in the current state of our planet. The changes are not part of a natural flux in the affairs of life on Earth. To those who prefer "God's Creation" to "biodiversity" and posit only a short history to life on Earth, the position is simpler. Unless we change our current actions, we will likely commit a third or more of all Creation to an inexorable path to extinction within the next few decades.