The 1988 arrival of viral hemorrhagic disease (VHD) in Spain devastated that country's European rabbit (Oryctolagus cuniculus) population and, in the process, possibly doomed the local species most adapted to hunt rabbit, the Iberian lynx (Lynx pardinus).

The wildcat is now critically endangered, with an estimated 100 to 200 animals remaining in the wild. That makes them the world's most endangered feline species. The species numbered 4,000 animals in 1960.

One of the few areas where Iberian lynx still reside is Spain's Doñana National Park. According to research published in the March 2011 issue of Basic and Applied Ecology, the lynx was the only predator in the park not able to adapt to eating other prey when the rabbit population crashed.

"All the carnivores reduced their consumption of rabbits following the arrival of VHD, although this reduction varied from one species to another," lead author Pablo Ferreras, a researcher at the Research Institute on Cynegetic Resources in Ciudad Real, Spain, said in a prepared statement.

According to the research, predators such as the badger (Meles meles), fox (Vulpes vulpes) and Egyptian mongoose (Herpestes ichneumon) all turned to other small mammals, birds and ungulate carrion for food when the rabbits became less plentiful. Badgers, for example, reduced the amount of rabbit in their diets from 71.8 percent to 26.2 percent.

But the Iberian lynx was not able to make that switch; it still relies on rabbits for 75 percent of its diet.

Why was the lynx unable to adapt? Ferreras told me that the lynx evolved on the Iberian Peninsula during the Pleistocene epoch glacial periods at the same time as the European rabbit. "The body size of the Iberian lynx, smaller than its evolutionary ancestor, is a result of its adaptation to preying upon rabbits, smaller than the ungulates, which constituted the main prey of its ancestor," Ferreras says. "Also the hunting behavior of the Iberian lynx—by ambushing and stalking—is an adaptation to hunting rabbits in patchy Mediterranean shrubs, where large rabbit densities originally occurred."

According to Ferreras, the lynx uses Mediterranean scrubland more than any other habitat, and relies on the presence of both rabbits and shrubs to thrive. "Lynx cannot survive in areas with high rabbit densities but without Mediterranean shrubs," Ferreras says. Much of the lynx's former scrubland habitat has been lost to human development.

The shrinking supply of its major prey source has not only affected the lynx's ability to feed itself, it has altered the species's social structure. Ferreras and his team found that female lynx increased the size of their territories, whereas juvenile lynx did not disperse from their nesting areas the way they used to. The researchers are calling on managing the rabbit population either through restocking or habitat improvement in order to save the cat from extinction.

Ferreras says that restocking the park with rabbits would not present an ecological problem, as most famously happened when rabbits were introduced to Australia, because the species is native to the region and there are so many other predators to help control their numbers. The Iberian Peninsula is "a large community of 30 to 40 natural predators, from reptiles to raptors and carnivores," Ferreras says. "The few places where rabbits are perceived (probably subjectively) as a pest in the Iberian Peninsula are mostly agricultural areas, where predators are very scarce. This is not the case of the landscapes where lynx can be recovered and where we propose to increase rabbit numbers."

VHD is the second plague to hit rabbits in Spain. The first was myxomatosis, a rabbit-specific disease that was purposefully released in France in 1952 by a doctor who wanted to keep rabbits out of his garden. It spread to Spain a couple of years later, where it killed 95 percent of the country's rabbits and kick-started the precipitous decline of the Iberian lynx. VHD, which also only affects rabbits, was first observed in China in 1984. Its origins are unknown.

Photo by José María Alvarez. Used under Creative Commons license