April 7, 2015, by Tim Radford
Finding sufficient grazing has become a serious problem for the Arabian oryx.
Image: Charlesjsharp via Wikimedia Commons
Global warming is the suspected cause of the series of dry years in Arabia that have brought starvation to a desert species saved from extinction. LONDON, 7 April, 2015 − One of conservation’s triumphs – the reintroduction of the oryx to the deserts of Arabia – could be at risk because of climate change, according to a new book. The animal already beautifully adapted by thousands of years of evolution to an arid environment met a problem on its return: even deserts have droughts. The Arabian oryx had been hunted almost to extinction before a handful were captured in 1962 and flown to Phoenix, Arizona, as the nucleus of a captive breeding programme. By 1972, the last wild oryx had been captured or killed in Oman, but the bloodline survived in captivity. The first reintroductions to the wild began in 1982, and numbers began to increase. There were incursions by poachers, but there were more releases. However, there have been so many dry years over the last two decades − according to Malcolm Smith, once chief scientist for the Countryside Commission in Wales, in his new book, Back from the Brink − that many of the newly-wild oryx have not been able to find sufficient grazing.
The animal is one of the most closely monitored in the world. Of all recorded deaths, 19% have occurred in fights between males, 13% have been due to poaching, and 65% have been due to starvation. The succession of particularly dry years in the region might be due to global warming as a consequence of human combustion of fossil fuels. Since climate simulations seem to predict that, in general, moist regions will get more rain and dry regions will experience ever drier regimes as greenhouse gas levels build up in the atmosphere, things don’t look good for the oryx − although captive populations for the time being remain secure. Other recently-rescued species may face even leaner times − once again, because of climate change. Spanish and Portuguese authorities have established safe territories for the Iberian lynx and, by 2013, more than 300 lived wild in Spain, while 150 lynx paced the enclosures in the breeding centres awaiting reintroduction. But the wild rabbit makes up 90% of the lynx’s diet, and rabbit numbers are limited by hunting and by outbreaks of myxomatosis and rabbit haemorrhagic disease. There have been fears too, that southern Spain and Portugal may become too hot and dry to sustain the prey, let alone the predator. Such threats to biodiversity, and to individual animals, are not new. Climate change has in various ways reportedly threatened Arctic marine mammals, creatures of the Borneo forests, and chimpanzees in isolated woodland in West Africa. Whole ecosystems that evolved in geographical climate zones may be doomed to sudden and rapid change. But Malcolm Smith’s book concerns itself only with the choicest last-minute success stories of conservation bodies: with those creatures that were all but gone when the conservationists stepped in. They were hunted, their habitats had been destroyed, and their ecosystems were always precarious. But climate change was, at the time of rescue, the least of their problems.One instance he explores shows just how intricate the living arrangements of charismatic species can be, and illustrates the finely-balanced play of climate and ecological stability in preserving a species. The Large Blue butterfly (Maculinea arion) exists in respectable numbers worldwide, but became all but extinct in the UK − with changes in farming practices and land use the suspected causes.
Until 1972, nobody quite understood the peculiar lifestyle of the Large Blue. It lays its eggs on the flower bud of the wild herb, thyme. A larva hatches and, after an initial vegetarian diet, falls off the plant. Thereafter, its life depends on just one species of red ant, Myrmica sabuleti. The Large Blue grub secretes a fluid that somehow suggests that of a red ant queen grub, so the ants take it home and nurse it. The Large Blue caterpillar turns carnivore and, for 10 months, feeds on red ant larvae. In pupate form, it makes queen ant noises and the ants continue to protect it. It hatches, gets out to the open − still protected by the ants − and flies off. It then has about a week in which to find a thyme flower bud, mate, and lay its eggs. But the complexities multiply. The thyme flower bud that bears the eggs must be within metres of the right kind of red ant nest, or the larva perishes.
Dependent on temperature
The grass above the ant nest must be closely grazed because the ants’ survival is dependent on temperature, and if the grass grows even a centimetre ground is shaded, the nest temperature drops by 2°C to 3°C, and the ant colony is at risk − along with any parasitic caterpillars in the nest. So the thyme has to flower at the right time, very near a red ant nest, the herbage has to be closely cropped, and the temperatures have to stay near the optimum. If anything goes wrong, there are no surviving Large Blue larvae to pupate. If things go well, and too many Large Blue grubs are taken into a colony, the ant larvae are all consumed, and both ants and butterflies perish. And then there’s the climate question − one that affects almost all insects. “Overall, butterfly populations have moved northward by about 75km in the last 20 years as overall temperatures have risen,” Smith writes. “They are likely to move yet further.” – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.