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 5,614km 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 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 McInturff. 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 (角马) migrations.
Not every creature fares badly. Hawks (鹰) 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 (啮齿类动物) have suffered as a result. Some have been brought to the edge of extinction.
