Rocky Mountains Separate Canadian Lynx, Study Says

John Roach
for National Geographic News
September 3, 2003
The Canadian lynx (Lynx canadensis) may creep for miles through dense, debris-strewn forest for the chance to pounce on a scarce snowshoe hare (Lepus americanus), but the stealthy feline is apparently seldom bothered to weather a crossing of the Rocky Mountains to find a mate.

Evolutionary ecologist Nils Chr. Stenseth together with geneticists Kjetill Jakobsen and Eli Rueness at the University of Oslo in Norway, and colleagues from Canada and Sweden, performed a large-scale genetic analysis of the elusive cat throughout its North American habitat and found populations of genetically distinct animals.

According to the study, published in the September 4 issue of the journal Nature, the Rocky Mountains appear to constrain east-to-west and north-to-south mixing of Canadian lynx populations in the western portion of its North American habitat, and an invisible barrier constrains north-to-south mixing of populations in eastern North America.

"What does come out very clearly in our study is that the genetic differences between the regions…are clearly significant, although small," said Stenseth. The differences suggest that some mixing of populations occurs but not at the levels required to make all populations similar.

Blocked Gene Flow?

Researchers and conservationists are trying to determine the geographic range of the Canadian lynx populations so that they know the extent of habitat conservation required for the species. Should efforts be focused on isolated pockets or continuous stretches of land?

The historic range of the Canadian lynx is from Alaska across Canada and into much of the lower 48 continental United States, but researchers have been uncertain as to how much cats from different parts of the species range interact.

While still abundant in Alaska and Canada, the feline is now scarce in the lower 48, where viable populations are known only in Maine, [Minnesota, Montana, Washington, Wyoming, and Colorado. In March 2000, the U.S. Fish and Wildlife Service listed the lynx as threatened in the lower 48 under the Endangered Species Act.

Scott Mills, a wildlife biologist at the University of Montana in Missoula, co-authored a genetic study published in the January 31, 2002 issue of Nature that compared Canadian lynx populations from various regions throughout its western range and found them to be genetically similar, suggesting high gene flow throughout the entire region.

Based on this research, Mills and colleagues suggested that corridors of land linking one population with another, even on either side of the Rocky Mountains, are needed to protect the species.

Mills said the genetic data collected by Stenseth and colleagues is an important and solid contribution to this field of research, but that their interpretation of the data is problematic.

"The data are not consistent with a conclusion that the Rocky Mountains are a barrier," he said. According to Mills, the data show very little genetic differentiation among lynx populations, "which implies considerable gene flow."

Stenseth, however, said the differences between the populations are distinct enough to suggest the populations do not fully mix. He said this is particularly clear when comparing eastern populations, which are separated by distance and not a topographic feature such as a mountain range.

"Distantly located populations are typically different because of them being distantly located from each other," said Stenseth. "In our case they are clearly more different, hence the observed differences are clearly real."

Lynx Conservation

According to Stenseth and colleagues, the genetic differences among the lynx populations correspond to ecological divisions between the populations. For example, populations in the wetter regions west of the Rocky Mountains are different than those in drier regions to the east. In turn, these populations are distinct from those in cold, snowy Maine.

"Our study suggests that the Canadian lynx is genetically structured following ecological differentiation, which seems to be due to large scale climatic factors," said Stenseth, who was part of a team that published a paper in the August 13, 1999 issue of Science that found Canadian lynx populations were divided into three separate climatic regions.

Based on the analysis of the genetic data, Stenseth concludes that conservation efforts for the Canadian lynx ought to be focused on these three distinct regions, classified as Pacific-maritime, Continental, and Atlantic-maritime.

Mills, however, said that the data collected by Stenseth and colleagues "reflects high gene flow on a range-wide scale, underscoring the conservation recommendations that he and his colleagues made in 2002.

"This data set is similar to ours in showing that connectivity is an important process for lynx," he said. "Therefore, in the U.S., it may be at least as important to focus on maintaining connectivity with the northern populations as it is to manage areas where lynx are currently found."

Lori Nordstrom, a biologist with the U.S. Fish and Wildlife Service in Helena, Montana, said the agency is required to use the best scientific information available when making conservation management decisions under the Endangered Species Act. The new study, she said, is a welcome contribution.

"There is so little information on lynx genetics at this point that it is all new information," she said. Resources on Big Cats

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