In early September this year I spent a few days in Norway, staying on the beautiful Hardangerfjord with my brother and his wife. One day, we drove to the village of Kinsaruk, and hiked up to see the Husedalen waterfalls. Kinsaruk is right on the edge of a vast rocky mountain plateau called Hardangervidda, the largest such environment in Europe and Norway’s largest national park.
One of the many reasons that Hardangervidda is ecologically important is because it is home to the largest population of wild reindeer in Europe, with a winter population of up to 7000 individuals). Historically, these animals roamed across Europe but today suitable habitat has become much more fragmented: in Norway there are 23 reindeer sites, but at 3500 miles2 Hardangervidda is the only area large enough to allow herds to roam freely, and for this reason supports the greatest number of Norway’s 30 000 or so wild* animals.
A shock then, to learn that only the week before my visit, 323 individuals were discovered dead on Hardangervidda. There had been a brutal storm, and it is thought the unlucky animals’ tendency to huddle together in bad weather may have backfired: this, together with the ground being waterlogged, meant that when lightning struck its deadly current rapidly spread through the surrounding ground and into the clustering animals. Not only that, reindeer morphology (large enough for current to flow between their legs) makes them ideal electrical conductors. Photos of their bodies littering the hill showed the chilling reality of this chance event.
Wild reindeer are the European equivalent of North American caribou: they are the same species, Rangifer tarandus, with subspecies reflecting local adaptation. In the latest IUCN Red list of Threatened Species, Rangifer are classified as ‘Vulnerable’, due to a 40% decline in populations over three generations. While the recent freak event seems like a mass event to us (probably because they are a large, charismatic mammal), it isn’t likely to impact their conservation level.
But it got me thinking about the influence of chance events on animal populations. The most destructive had to be the asteroid impact which wiped out the dinosaurs. A recent study concluded that it was a colossally unlucky event, not just because the planet was blasted by a massive lump of rock hurtling through space, but because it was a particularly bad time for this to happen. According to experts, dinosaurs were already struggling with rising sea levels and increased volcanic activity, so the asteroid hit while they were at their most vulnerable; it was, according to one expert, a “perfect storm of events” that wiped them out. Had it hit a couple of million years earlier or later, the dinosaurs would have been in a much stronger position to cope. So that’s bad luck for the dinosaurs, but good luck for us – had the asteroid not hit when it did, there’s a chance that dinosaurs would still roam the earth and mammals may never have been able to diversify and evolve as they did.
On a smaller scale, I remember a final year lecture on conservation biology, in which we learned about the plight of the unfortunate Stephens Island Wren, said to be the only species wiped off the planet by a single individual – in this case, a cat called Tibbles. Flightless, nocturnal little birds, the Stephens Island Wrens had evolved to fill the niches of mice and other small rodents that did not exist on the island. They also lacked anti-predator adaptations, so overall were a stupendously easy target for a predatory animal. The story goes that Tibbles, a pregnant female, was set free on the island after a ship was forced to dock in a storm in 1894. A lighthouse had just opened on the island so Tibbles started associating with the keepers and their families, and in due course depositing ‘gifts’ of the island’s wildlife at the door. One of the keepers, David Lyall, was interested in birds, and intrigued by the presence of a small wren among the cat’s victims. He sent it to a naturalist friend, who confirmed it was a new species. But in the meantime, Tibbles had been busy: she is said to have brought 11 individuals back to Lyall which, with an estimated breeding population of just 10 pairs on the island, was catastrophic. It may not have been just Tibbles, for remember she was pregnant, and the feral cat population on Stephens Island soon spiralled out of control (by 1912, when a cat eradication scheme was in place, 700 were shot), but she certainly made easy prey of this unusual bird.
Chance events don’t just negatively impact nature. Take the case of Père David’s Deer, a long-tailed, semi-aquatic species native to China that was on the brink of extinction in the nineteenth century. The only viable population existed inside the Emperor’s 200 km2 Nanyuang Royal Hunting Garden, which had been walled off from the outside world since the 13th Century, and was closely guarded. The chance event was the visit and tenacity of Père Armand David, a French naturalist who heard of the deer and travelled to see them. Persuading the guards to have a look (something which should have been forbidden), he realised the deer were unlike any known to Western science, and arranged for skins and skeletons to be sent to Paris. The species was named Père David’s Deer in 1866, and subsequently some deer were introduced into private collections across Europe. Here’s where the chance event became really important. Because by the end of the nineteenth century the Nanyuang herd was in serious trouble, the result of a massive flood in 1895 demolishing the outer wall of the garden and enabling many animals to escape (and be hunted). Only 20–30 animals survived in the garden, but these were finished off in 1900, during the Boxer rebellion, when soldiers occupied the garden and shot them for food. Wiped out in their native China, that should have been the end of Père David’s deer. But those animals that had been shipped to Europe still survived so, realising the perilous position in which the species found itself, in the early 20th century the Duke of Bedford gathered the last 18 animals together to form a breeding herd at Woburn Abbey Estate in England. Only 11 of these were capable of reproducing, but incredibly, they did reproduce and the species started to recover, seemingly escaping the potentially severe consequences of their extreme genetic bottleneck. The first animals were sent to Beijing Zoo in 1956, and although the species is listed as ‘Extinct in the Wild’ by the IUCN, it is possible that one day free-ranging animals may once again roam the marshes of China.
Chance events are essential for evolution; they provide the basis for variation upon which natural selection can act. But it is when populations dwindle that chance events take on a more significant role, and they can make or break a species’ chance of surviving. The Hardangervidda’s reindeer population will rebound and recover, but with many species on the brink of extinction, the effects may be severe when fate next deals the chance card.
*This number includes semi-wild animals too. For more precise figures on reindeer population estimates check out the IUCN’s page: http://www.iucnredlist.org/details/summary/29742/0