BIODIVERSITY:Invading Aliens Threaten Native Plants Worldwide

Invading alien species are responsible for a worldwide biodiversity crisis, driving to extinction large numbers of native plant and animal species on every continent. The IUCN, the World Conservation Union, said recently that common species such as the domestic house cat and the starling are part of the problem. They and hundreds of other invasive alien species are moving outside their natural range and threatening the existence of native plants and animals. "After habitat loss, this biological invasion constitutes the greatest threat to biodiversity, and it has already had devastating consequences for the planet," said the Union's chief scientist.

"The economic bill runs into tens of billions of dollars every year. Pests, weeds and pathogens, introduced deliberately or accidentally, reduce crop and stock yields, and degrade marine and freshwater ecosystems," he said.

The United Nations Environment Programme and the Secretariat of the international agreement to conserve the diversity of species, known as the Convention on Biological Diversity, are trying to promote awareness of the perils facing all the world's species. This year they are calling attention to the management of invasive alien species. The IUCN said the world's worst 100 alien invaders include the gray squirrel, the domestic cat, the Indian myna bird, the Asian longhorned beetle, the sweet potato whitefly, the Asian tiger mosquito, the yellow Himalayan raspberry, Koster's curse, the starling, mimosa, the shoebutton ardisia, the red-vented bulbul, the erect pricklypear, and the mile-a-minute weed.

"Some particularly notorious cases are listed, but that does not mean that a species absent from the list is any less dangerous. Our purpose in publishing the booklet is to draw attention to the scale and complexity of the rapidly growing invasive species problem. But it is really only the tip of the iceberg, said an ICUN specialist.

The crazy ant, the brown tree snake, the small Indian mongoose, the Nile perch, strawberry guava, the water hyacinth, the zebra mussel and the brushtail possum are all wonderful species in their own habitats, he continued, but like unwanted house guests they can take over ecosystems to which they are alien species.

Crazy ants, so-called because of the way they move, have invaded native ecosystems and caused environmental damage from Hawaii to the Seychelles and Zanzibar. On Christmas Island in the Indian Ocean they killed three million crabs in 18 months. These red land crabs played an important role in the island's forest ecosystem by eating leaves and seedlings of rainforest trees. Crazy ants also prey on, or interfere with, the reproduction of a variety of reptiles, birds and mammals on the forest floor and canopy. Brown tree snakes lived in Australia, Indonesia, Papua New Guinea and the Solomon Islands until one day in the late 1940s or early 1950s one hitchhiked on a military aircraft to Guam, a previously snake-free island. The lack of natural predators and the presence of ample prey allowed the brown tree snake population to explode. By the 1970s this poisonous reptile had nearly exterminated Guam's native forest birds. This snake threatens the biological diversity of other tropical islands because it can conceal itself in the cargo of ships and planes, or in aircraft wheel-wells. It has reached Micronesia, Hawaii, the mainland US and Spain.

The large purple and violet flowers of the South American water hyacinth make it a popular ornamental plant for ponds. But it is one of the worst aquatic weeds in the world. Now found in 50 countries on five continents, water hyacinth can double its numbers in only 12 days. Infestations of this weed block waterways, interfering with boat traffic, swimming and fishing. Water hyacinth also prevents sunlight and oxygen from reaching the water column and submerged plants. Its shading and crowding of native aquatic plants dramatically reduces biological diversity in aquatic ecosystems.

Dr. Wendy Strahm, the World Conservation Union's plants officer, warns, "The effects on biodiversity are immense and often irreversible, and yet awareness of the problem is alarmingly low." Founded in 1948, the IUCN includes some 10,000 scientists and experts from 181 countries in a worldwide partnership to influence, encourage and assist societies throughout the world to conserve the integrity and diversity of nature. The IUCN website is at: www.iucn.org. For native plants in the Pacific Northwest and related links, go to the Washington Native Plant Society: www.wnps.org.

CONTROL NON-NATIVE PLANTS

A recent newsletter from the Union of Concerned Scientists says people should put only non-invasive species in own gardens. Invasive species can spread by wind, pollen, water and birds. [www.ucsusa.org]

INTACT HABITAT HELPS BIODIVERSITY

(ENS) - While most conservation planners focus on preserving certain areas, new research shows that an area's surroundings may be just as important. A study in the journal Conservation Biology shows that the diversity and abundance of certain animals living in fragmented habitats is higher when they are near intact or less disturbed habitats. The researchers determined the diversity of ground foraging ants in and around La Montanita, a tropical mountain forest reserve in southern Chiapas, Mexico. They used ants as an indicator of biodiversity because insects are the most diverse group of species, and ants comprise most of the insect mass in the tropics. The reserve lies between two types of coffee farms: a shady, organic farm that has been planted with native trees, and a sunnier, conventional farm that uses pesticides and herbicides. The authors found that the number of ant species was similar in the forest fragment and the shady, organic farm - 23 versus 16 species. But diversity plummeted on the conventional farm, which hosted just seven species. They also found that while ant diversity on the farms decreased with distance from the forest fragment, this drop off was much slower on the shady, organic farm. On the conventional farm, ant diversity had already dropped to its lowest level just 65 feet from the fragment. The researchers conclude that rather than connecting fragments with habitat corridors, in some cases it would be more effective to focus on making the area surrounding the fragments more conservation friendly. "Attention to the agroecosystem that makes up the majority of the matrix may be key to conservation at the landscape level," they wrote.