Planet's Wildlife Growing More Alike, Experts Warn

James Owen
for National Geographic News
November 11, 2005
Big Macs in Bejing, Wal-Mart stores across Brazil, The Simpsons in Arabic on Egyptian TV: Such is the homogenized nature of modern culture.

But it isn't only human society that's becoming increasingly globalized. Biologists say wildlife, too, is growing more alike everywhere you go.

Researchers warn that human impacts on the environment are fuelling the global spread of animals and plants, which are replacing regionally distinct species.

Known as "biotic homogenization," it's a phenomenon that "elicits serious concern among conservationists as a major threat to regional individuality," according to University of Wisconsin biologist Julian Olden.

Olden is among a small but growing number of scientists investigating a process he likens to the "rapid spread of big-box retailers" at the expense of local "mom-and-pop businesses."

"We are just starting to understand the subtle aspects and implications of biotic homogenization," he added.

Natural history writer David Quammen says we're entering an age where "virtually everything will live virtually everywhere, though the list of species that constitute 'everything' will be small."

The list includes rampant weeds, cultivated fish, street-wise rodents, brainy birds, and invasive mollusks.

As a result, scientists say, life on Earth is becoming increasingly impoverished, and we have only ourselves to blame.

Dangerous Waters

Perhaps the most obvious threat to nature's regional variety comes from invasive, nonnative species, which have capitalized on the growth in global transport and trade.

The zebra mussel, for instance, has spread via ships and boats across Western Europe and North America.

Native to Eastern Europe, the hitchhiking mollusk represents a major threat to freshwater ecosystems by disrupting food chains and crowding out native animals.

Last month the species was voted the number one threat to U.K. wildlife at a public debate in London hosted by the environmental nonprofit Earthwatch.

"No one is safe from the zebra mussel," warned zoologist David Aldridge of Cambridge University, England. "They are choking the habitats of our birds and fish and smothering our native mussels."

Zebra mussels also block water pipelines and cause costly damage to boats, harbors, and power plants. U.S. companies now spend around three billion dollars a year trying to eradicate the species.

As for nonnative plant invaders, among the most infamous is kudzu, a fast-growing vine first introduced to the U.S. from Japan in the 1870s.

Kudzu has since spread wildly out of control in the southeastern U.S. Capable of growing a foot (30 centimeters) a day, it smothers and kills other plants, even uprooting shrubs and trees.

Brainier Birds?

A bigger threat to regional biodiversity comes from changes in land use, experts say.

The fragmentation of habitat and ongoing urban development are creating increasingly uniform landscapes that favor the same sorts of animals.

Known as "generalists," such animals include cockroaches, crows, rats, raccoons, red foxes, and various deer.

A recent study of bird population trends in U.K farmlands over the past 40 years linked the intensification of agriculture with the rise of generalist, "brainy" species.

The study suggests birds with relatively larger brains have coped much better with Britain's changing rural environment.

So while partridge populations have fallen 75 percent, farmland magpie numbers have increased more than 70 percent.

"If one set of resources becomes scarce, and you're a small-brained bird, perhaps you aren't able to do much about it, as you don't have much flexibility in your behavior patterns," said study co-author Tim Blackburn, ecology professor at Birmingham University in England.

"A larger-brained bird may have the ability to innovate, so they can switch behaviors or utilize novel foods."

Magpies, a species of crow, have proved equally at home in urban habitats, with the overall U.K. population more than doubling in the past 40 years.

Other birds that have risen to the top of the pecking order in Western cities and suburbs include pigeons, starlings, and feral parakeets.

Julian Olden says birds are key indicators of biotic homogenization caused by urbanization.

"Research suggests the biota of urban centers in distant cities are becoming more and more alike by the increasing occurrence of cosmopolitan exotic birds, like the European starling, and the loss of regional birds that previously defined the uniqueness of these areas," he said.

Standardized Animals

Individual species are also becoming standardized, experts say, with cultivated strains of animals and plants ousting local varieties.

Take the brown trout, a popular quarry with many sport anglers.

Bred artificially to supplement natural stocks, farmed brown trout are wiping out wild European trout populations, according to Michael Hansen, senior scientist at the Danish Institute for Fisheries Research in Silkeborg, Denmark.

Virtually all cultivated brown trout are originally Atlantic in lineage, he says, but "they have been exported and stocked in massive numbers in southern European rivers inhabited by other lineages."

The result, Hansen says, is that endangered strains such as the marble trout of the Balkans region are now vanishing.

"There are now almost no populations left that have not been severely hybridized with stocked, cultivated Atlantic [brown] trout," he added.

There are similar fears over industrial-scale salmon farming in countries such as Norway and Scotland, where large numbers of fish-farm escapees have been found crossbreeding with genetically unique wild Atlantic salmon.

"We are reducing the genetic resources of wild populations," Hansen said. "It is unfortunate that genetic variation is eroded when at the same time global warming and other environmental changes due to human influences make it even more important that populations have the building blocks to adapt to the new conditions."

Julian Olden agrees, saying that biotic homogenization "may compromise the resilience of ecosystems to future environmental change."

And, Olden adds, it's not just wildlife that's becoming impoverished but our own quality of life—especially for people who marvel over, and love to explore, nature's global diversity.

"Greater biological homogeneity will influence not only how we view the world but also our motivation to experience it," he said.

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