+quot;Biosphere Decay?+quot; by Alan McGowen In the past I have posted several articles ab

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================================================================= "Biosphere Decay?" by Alan McGowen In the past I have posted several articles about ecosystem decay and the effects of habitat fragmentation, extinction processes viewed from the standpoint of systems theory, and the like. Here I would like to raise a question which is worrying many conservation biologists today. I have explained how an ecosystem can lose species as a decay response to stresses of various kinds such as loss of habitat area and habitat fragmentation. The question is, are we seeing such a decay process on a planetary scale? The problem is a little bit like global warming. Nobody doubts that injecting greenhouse gases into the atmosphere can change its energy balance in principle, but the details are complex and it is uncertain whether global warming has been observed as yet. In like manner, nobody doubts that loss of habitat and stress on habitat can cause *local* extinctions, and large numbers of these occur every year. But the biosphere as a whole is also an ecosystem; it is conceivable that once a certain amount of damage has been done to it an ecosystem decay process could set in at a *global* level. But has anything of the sort been observed? If it were observed, how could we distinguish it from extinction due to more local causes? There are some alarming trends that have appeared in recent years which look rather like such a process. One of the most alarming is the worldwide phenomenon of amphibian population declines. Amphibians are particularly sensitive indicators of ecosystem condition and have been declining almost everywhere they occur. While many of the declines can be explained by obvious local events such as wetlands loss and pollution, declines are also now well documented in many preserves and areas that are considered extremely isolated and unperturbed, and large enough that ecosystem decay was not anticipated. Yet the declines are occurring. It is impossible to believe that worldwide declines in an entire class can be a coincidence, yet if the declines in the (supposedly) undisturbed preserve areas are not a coincidence, they imply that either our understanding of ecosystem decay is missing something and the phenomenon is easier to produce than we thought, or that possibly some biosphere level decay may already have begun. Since our understanding of coevolved dependencies is only about 20 years old it is unlikely that we know most of what there is to be known about it, and there may be more connections between the local ecosystem level and the biosphere level than we are presently able to account for. Or perhaps some subtle global pollution effect is at work, though no specific agent has been identified. This alarm may not seem as loud or as frightening as ozone depletion or greenhouse warming, but it is potentially far more dangerous than either of those (except insofar as they contribute to further extinction), since the duration of those phenomena is expected to be at most a few centuries, and the duration of biodiversity loss is tens of millions of years -- i.e. forever on socially meaningful time scales. The unexplained loss or decrease of populations is by no means restricted to the amphibia, but it has been most consistently seen in that group. Some university research groups and clearinghouses have been set up to investigate this problem, but it has only recently graduated above the level of awareness of anecdotes traded among herpetology specialists. The entire conservation biology community is now also aware of it, and it is time for the larger scientific and student community to be aware of it as well. Perhaps as thinning eggshells told Rachel Carson that DDT was accumulating in the food web, the worldwide decline of yet another class of vertebrates contains a message of even more ominous import, precisely because no obvious culprit such as DDT has been found. -------


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