A WORLD OF BARRIERS

In 2015, construction began on more border walls worldwide than at any other time in recorded human history. Barriers between Russia and Ukraine, Burma and Bangladesh, Mexico and Guatemala, Turkey and Syria have all gone up in the past few years, largely motivated by fears of terrorism and increasing human migration. A total of 63 walls were built or under construction by the end of 2015, compared with fewer than 20 when the Berlin Wall came down in 1989. Here are four examples of how barriers are affecting wildlife in Europe, Asia and Australasia.

1 CZECH REPUBLIC/GERMANY 815km fence

Reason for border: During the Cold War, the Iron Curtain was heavily guarded and electrified. Impact on wildlife: The Iron Curtain fell over 25 years ago but red deer on the border between the Czech Republic and Germany still do not cross the divide, which is now forest and open land with no barrier. A study of 300 deer found the animals on each side of the border maintained old boundaries and were completely separate populations.

2 MONGOLIA/CHINA 4,710km fence

Reason for border: The original fence was built following a border treaty in 1962. In 2008, the Chinese built a 100km fence to protect livestock from wolves. Impact on wildlife: Khulan, or Mongolian wild asses, were fitted with GPS collars in a 2013 study, which demonstrated that the fence presented an absolute barrier in the south-east Gobi Desert. While the barrier restricts wild ass movement and migration between countries, the border area has become a grazing refuge for the animals in harsh winters.

3 CROATIA/SLOVENIA 670km razor-wire fence

Reason for border: Reduce flow of asylum seekers from Syria and Iraq. Impact on wildlife: 349km of the fence cuts through the Dinaric Mountains that contain one of the most important wolf populations in Europe. Out of 10 wolf packs, five have their home ranges in both countries. While some wolves have shown an ability to cross, there is no guarantee they will remain connected with their core population in the south. There is a chance the populations will become isolated and inbreed.

4 AUSTRALIA 5,531km fence, Queensland

Reason for border: To protect domestic sheep from dingo predation. Impact on wildlife: The north-western side of the fence habituates a larger dingo population and subsequently kangaroo and emu numbers have fallen due to predation. But fewer dingoes on the southern side has led to an increase in kangaroos there. Where dingoes have been exterminated altogether, a rise in numbers of red foxes (an introduced species) has led to a reduction in small native mammals, including bandicoots.