If the Po`ouli does not recover, it will become another statistic giving force to an increasingly accepted notion among biologists that the Earth is on the verge of a massive species meltdown. And, according to this notion, the oceanic islands, such as the Hawaiian archipelago, are taking the first hits.
Hawai`i’s avifauna has already suffered tremendous losses. Before human contact, the Hawaiian chain had more than 100 species of birds found no place else on Earth, as known from the fossil or subfossil record. Nearly half of them became extinct after the first humans arrived. Of those that remained by the time of Western contact, “we have chopped off a big block,” says Paul Banko, a biologist with the Biological Resources Division of the U.S. Geological Survey in Volcano, Hawai`i. And, Banko notes, as scientists discover more birds through the fossil records, “the numbers will only get worse.”
Over the last two decades, the record of fossils (mineralized bones) and subfossils (non-mineralized bones) has contributed greatly to scientists’ understanding of the relative abundance and range of Hawaiian birds in ancient times. Some species that are now limited (including the Po`ouli) were more wide-ranging, while many of the nectivores that are now among the most common native forest birds (`I`iwi, `Apapane, Amakihi) were rare.
In a talk delivered two years ago to the Cooper Ornithological Society, meeting in Hilo, Storrs Olson noted that this change in abundance should make scientists think twice about what their goal is in species and habitat restoration. “There’s a good chance that large areas of `ohi`a,” which supports the nectivores, “may be man-caused, except on the Big Island,” Olson told Environment Hawai`i. On the other islands, he said, the forests may likely have been dominated by koa trees and insectivorous birds. “Clearing and burning may have led to the alteration of the forest,” and with it, the change in relative abundance of nectivores and insectivores, he said. Olson’s views on `ohi`a are viewed skeptically among many scientists. There is little disagreement, though, on his idea that we have today only a scant inkling of what a forest unaltered by human-induced changes might resemble.
“Hawai`i is not unique in any of this,” says Peter Vitousek of Stanford University. “Islands aren’t even unique. A very strong sense is that the combination of things that people are doing in almost every locality, and other things that are global in extent, are causing change in the way almost every organism on Earth must live.”
In 1997, Vitousek and several colleagues authorized an article in Science that provided an overview of the ways in which human actions had affected the Earth’s ecosystems. “Extinction is a natural process,” they wrote, “but the current rate of loss of genetic variability, of populations, and of species is far above background rates; it is ongoing; and it represents a wholly irreversible global change.” *
In a conversation with Environment Hawai`i, Vitousek recounted the many dramatic changes resulting from human activities, including climate change, alterations of the natural nitrogen cycle, and the like. “Compared to loss of species in particular, they’re transient things. All of it is short-term. Really, if we stopped burning fossil fuels, stopped emitting carbon dioxide, the effect of that wouldn’t linger much past a couple of centuries. The same with the alteration in the nitrogen cycle and a similar time scale for most of the things we do. But species — genetically distinct populations that we drive to extinction — are truly irreplaceable. That’s a truly irreversible act, in a way that most things we do environmentally aren’t at all. Even chemical compounds that we regard as persistent in the environment — and there are some nasty things out there: DDT, PCBs, and others — they have lifetimes of decades, even a hundred years.
“We’ve probably already exterminated a quarter of the birds on Earth. The consequences are far past any chemical compound or any climate change we make.”
David Quammen, author of Song of the Dodo, describes the idea of impending mass extinctions in “Planet of Weeds,” an article in the October 1998 issue of Harper’s Magazine. “The concept of mass extinction implies a biological crisis that spanned large parts of the planet and, in a relatively short time, eradicated a sizable number of species from a variety of groups,” he writes. Five periods in particular stand out: The Ordovician, Devonian, Permian, Triassic, and Cretaceous — the best known, perhaps, but not the worst (only about three-quarters of all species were lost then, as against the Permian, when 95 percent of all known animal species were wiped out).
“The consensus among conscientious biologists is that we’re headed into another mass extinction, a vale of biological impoverishment commensurate with the big five,” he continues. According to ecologists Stuart Pimm and Thomas Brooks of the University of Tennessee, 50 percent of the world’s forest bird species will be extinguished by deforestation over the next 50 years, Quammen notes.
Nature won’t come to an end, of course. But, Quammen observes, it will certainly be different: “Virtually everything will live virtually everywhere, though the list of species that constitute ‘everything’ will be small… My label for that place, that time, that apparently unavoidable prospect, is the Planet of Weeds. Its main consoling felicity, as far as I can imagine, is that there will be no shortage of crows.”
* Peter M. Vitousek, Harold A. Mooney, Jane Lubchenco, and Jerry M. Melillo, “Human Domination of Earth’s Ecosystems,” Science, July 25, 1997.
— Patricia Tummons
Volume 9, Number 5 November 1998
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