A weekly series by UPI investigating potential connections of human activity to global climate change.
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BOULDER, Colo., July 12 (UPI) -- The Canadian lynx is a 3-foot-long cat with Frisbee-like feet that allow it run atop snow in pursuit of its favorite prey, the snowshoe hare.
The lynx is rare along much of its range, but it is cute and furry and relatively popular with people -- if not with snowshoe hares -- because it does not impinge much on human economic activity. The lynx is solitary and secretive, rarely seen. Some travel like Jack Kerouac. Researchers have documented individuals moving nearly 400 miles seeking if not a mate, then food, adventure or a better life -- whatever lynxes search for.
The researchers studying the arctic feline have found something else -- it seems to be benefiting from changes in climate. Global warming is making it a little easier for the lynx to catch its dinner.
University of Alberta biologist Stan Boutin, part of a research team that studies lynx-hare interactions in boreal forest ecosystems, has found that snow quality can affect the predator's hunting success.
The critical issue, Boutin reports in the current issue of the Proceedings of the National Academy of Sciences, is the hardness of the snow surface. Those Frisbee-like feet are designed to keep the lynx from sinking into the snow when it is running.
When the weather stays cold, the snow stays fluffy and the lynx sinks in a little more -- allowing the fittest and fastest hares to escape. When warmer spells are interspersed with frigid weather, however, the snow surface tends to form crusts, allowing the lynx to stay atop better, making its running -- and hunting -- more successful.
Boutin has collected more than 10 years of data on snow conditions and predator success.
"This lynx-hare cycle is an amazing phenomenon and it has proven a very robust relationship," he said. "If we start to get climate warming and a crusting of the snow without long, deep cold spells, it could change the interaction."
As in much of life, however, what is good for the lynx now might be bad for the lynx later. Over time, if the lynx's more robust predation suppresses snowshoe hare numbers, the lynx will begin to starve if it cannot find something else to eat. This would be extremely difficult, because its diet consists almost entirely of hares.
Meanwhile, reduction of the hare population -- the boreal forest's major herbivore -- also would substantially alter the structure of the plant community.
Climate change often requires adaptation by plants and animals, and the proverbial graveyards are littered with the bones of those that could not adjust quickly enough. Among previous extinction events attendant with climate change, scientists have found it can take up to 5 million years for an ecosystem's biodiversity to recover to pre-extinction levels.
If climate change occurs gradually, however, some studies indicate species can survive by migrating from one habitat to another.
Gregory Retallack, a geologist at the University of Oregon in Eugene, found that a slow cooling about 35 million years ago apparently caused substantial extinctions in the Pacific Northwest. He has written about the event in the July-August issue of the Geological Society of America Bulletin.
"Sixty percent of plants and 32 percent of marine invertebrates went extinct across the Eocene-Oligocene boundary," Retallack told United Press International.
The cooling took quite a while, perhaps 6 million years, he said, and amounted to about 12 degrees Fahrenheit (7 degrees Celsius) -- dropping from a global average of 67 degrees F (19.7 degrees C) to 55 degrees F (13 degrees C).
"The peak of the temperature was about 34 million years ago, then it declines with a few ups and downs, and doesn't really stabilize until you get to 28 million or 29 million years ago, at a level that is not amazingly different from today."
This cooling may have been carbon dioxide-related, Retallack said.
"There is evidence for a decline of CO2 levels, from something like three times the present concentration to very close to the present concentration," he said. "This does support the idea of a greenhouse mechanism for climate change."
For that amount of cooling to occur -- and be related to CO2 decline -- there must have been some mechanism that increased carbon sequestration. There are several candidate mechanisms, including the uplift of mountains and a change in ocean currents. The mechanism Retallack himself favors is the evolution of grasslands, a new type of continent-wide ecosystem, to absorb CO2.
"The extinction was not a big bang extinction like the Cretaceous-Tertiary extinction that wiped out the dinosaurs," he said. "What happened to the thermophilic taxa (cold-adverse animals) in our area was not that they necessarily died, but that they went south with the cooling climate. The modern relatives of the species that were here in Oregon -- both the marine organisms and the vegetation -- are still living in tropical regions."
Whether climate-adapted species will be able to migrate in the face of changing temperatures today is a major issue among biologists. The work of Retallack and colleagues indicates some adaptability over long timescales, but the more rapid change anticipated by the current warming trend -- on the order of 100 or 150 years -- leaves considerable uncertainty.
Russell Graham, curator of the Earth & Mineral Sciences Museum at Penn State University in University Park, Pa., said climate change seems to be the culprit behind the extinction of North America's large mammals around 11,000 years ago, at the end of the Pleistocene era, when mammoths, mastodons, giant sloths, giant beavers, camels, giant tortoise, horses, saber-toothed tigers and other monsters of the continental midway disappeared.
"In all," Graham told UPI, "North America lost 32 different mammal species."
North American climate toggled from cooler to warmer and back throughout the Pleistocene, which began about 1.8 million years ago.
"That caused the geographical ranges to become smaller," Graham said.
As food diversity diminished with colder climate, it restricted ranges for large animals and forced them to narrow or adjust their diets. When warmed climate toggled back, many found themselves locked into specific ecosystems.
"As the geographic range decreases, the probability of extinction goes up," Graham said. "Range is a function of body size. A mouse doesn't need a large area, (but) an elephant needs a large geographic space."
Extinctions at the end of the Pleistocene appear to be related to warming, he said, but what drove them was the climate fluctuation. Today, he added, climate change is again causing habitat destruction.
"The future problem is compounded by humans, because we have become a major driving force," Graham said, "and climate change will heighten the probability of extinction for animals that have small geographic distribution and large body size."
Climate change is not the only candidate for the Pleistocene extinctions. Other scientists suspect overhunting by humans, who migrated into North America around that time with new technology -- Clovis-point weapons. Still, Graham said though humans may be implicated in the extinction of mammoths and mastodons, the hypothesis cannot explain the loss of the other large animal species.
"There are lots of other things taking place at the time," he said. "Many animals reduced their body size. That's probably related to climate, and not to anything that humans were doing."
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Dan Whipple covers the environment for UPI Science News. E-mail [email protected]
