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(2023-雅礼十六校联考)Earth's longest artificial structure is usually said to be the Great
Wall of China while the second-longest is not a wall,but a fence.It stretches for 5,614 km
across eastern Australia and is intended to stop the country's wild dogs,the dingoes,from
hunting sheep.
Australia's dingo fence does not stand alone.Millions of kilometres of fences wrap the
world.Some are intended to limit the movement of animals,some the movement of people,and
some merely to mark the boundary.
Until recently,data on the effects of fences on wildlife have been inadequate.That has
changed with the publication of a report by professor Alex MeInturff.One discovery he has
made is that more than half of published fence research focuses on just five countries
America,Australia,Botswana,China and South Africa.A second is that only a third of these
studies examined the impact of fences on anything other than the target species involved,
meaning the animals purposely intended to be kept in or out.
Non-target species,however,are often those that have their fortunes most greatly
reshaped by the appearance of poles and wire.Australian fences intended to keep out dingoes
are also barriers to long-necked turtles,which travel great distances over land when moving
between nesting sites.In Botswana fences built to spare cattle from wildlife-borne disease
result in serious interference with wildebeest (migrations.
Not every creature fares badly.Hawks (in Montana gladly sit on newly built livestock
fences to hunt small animals,while fence-based spiders in South Africa outperform their
tree-based cousins when it comes to catching insects.
Often,though,the winners are creatures that cause trouble for existing ecosystems.
Keeping dingoes out of large parts of Australia has allowed aggressive red foxes to multiply.
Native rodents(W齿类动物have suffered as a result..Some have been brought to the edge of
extinction
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