Conservation Northwest

Predators and prey Badgers are amazing diggers and voracious hunters of ground squirrels and pocket gophers. © David Moskowitz "What's up with predators?" continued from page 5 sized hind legs and feet to run at lightening speed over snow. Their huge ears magnify the slightest sounds. Most ingeniously from a genetic standpoint, hares have developed a natural camouflage and change color with the seasons—white for winter, brown for summer. With so many things trying to eat them, they need lots of defensive weapons. The hares that live longest and have the most babies pass more of those successful genes to the next generation, refining the traits over time, like camouflaged fur, that allow hares to escape lynx and owls long enough to reproduce, thus ensuring the survival of the species and its competitive "fitness" to adapt to dynamic landscapes and dozens of hungry predators. Lynx are the ultimate hare specialists and as such their fortunes rise and fall with those of their big-footed prey. And they've kept pace in the evolutionary race for survival: their huge furry feet and long hind legs allow them to run and cut on top of snow like an NFL running back on juice. Many animals hunt hares but none with the efficiency of lynx. Yet they still can't kill all the hares. Wild fluctuations In the north of their range, hare numbers have historically "crashed" spectacularly before rising again dramatically. In Alaska and western Canada, hare numbers rise and crash in roughly 10-year cycles, sometimes going from 10,000 to fewer than three animals per square mile in a single year. Female hares can produce two to five litters per year with three to four young per litter. The phenomenon has been a source of scientific scrutiny for decades and was first described by fur trappers in the midnineteenth century. On large scales, scientists think that cyclical sun spot activity affects weather patterns and fire frequency in boreal forests, which in turn affect hare survival and food availability. On smaller scales, over-browsing by the hyper-reproductive hares at their population zenith leads to food shortages that cause starvation and reduced reproduction, which in turn start the population declines. Just as the health of individual hares diminishes and they become more vulnerable to disease, predation from a larger number of hungry hare eaters kicks in and bingo, hares are scarcer than hens' teeth—for a little while. In essence, such wild fluctuations "reset" complex multiple predator prey systems until the next crash, rather like the way our economic and regulatory systems work—or not. Since they're so tightly linked to snowshoe hares for food, lynx 6 Spring/Summer 2011 populations in the north rise and fall with them. Northern lemmings undergo similar population booms and busts. Snowy owls are so tuned in to lemmings that they actually lay fewer eggs when lemming populations are down. But such boom and bust predator prey economies are the exceptions, not the norms. From Arctic to Africa Bees swarm, birds flock, fish school, and ungulates such as elk form herds because they're less likely to become a predator's next lunch special if they do so. Why some predators form groups, on the other hand, like lions in prides or wolves in packs, could have less to do with food sharing and more with defense of territories and rearing of young. Research on the most well-known predator/prey dance partners on earth has shown that Africa's Serengeti lions and wildebeest coexist in relative stability without the dramatic fluctuations in numbers that typify some arctic predators and prey like lynx and hares and lemmings and snowy owls. The niches, or jobs, of each species are crafted over millennia by natural selection. A research team lead by John Fryxell of University of Guelph in Canada and Craig Packer from the University of Minnesota wanted to know why. Their modeling of four decades of data showed that wildebeest drastically reduced lion predation when they kept to groups and large herds. Interestingly, the greater the tendency to form groups, the higher the stability of numbers of both species over time. According to Fryxell and colleagues: "When both the lions and wildebeest formed groups, predation was reduced even more. Compared with no-group ecosystems (all animals strewn across the Serengeti), grouping caused a 90-percent reduction in kill rates for lions." The complex social "cliques" seemed to work as ecosystem stabilizers, not dissimilar to human communities, with "both lion and wildebeest populations remaining relatively level over time." Social cliques among wild animals in the Serengeti are actually the glue that holds the ecosystem together and keeps population numbers stable. Wildebeest thrive in great numbers alongside zebra, Thompson's gazelles, and several other ungulate species, all prey for lions, leopards, hyenas, crocodiles, hunting dogs, and cheetahs. Wolves and white-tails There are 3,000 wolves in Minnesota. They eat on average about 50,000 of the estimated 450,000 white-tailed deer a year. This represents about 11.5 % of the deer population, with minimal supplements of snowshoe hares, beavers, and moose. www.conservationnw.org

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