October 9, 2012
Researchers Find Cougar Migration Patterns Not What They Expected
Alan McStravick for redOrbit.com - Your Universe Online
In a recent study that appeared online in the August early-view edition of the journal Molecular Ecology, researchers looked at DNA in tissue samples that had been collected from 739 mountain lions over a period of seven years. The purpose of the study, the first to be conducted on such a large scale, was to discover population structures and history and to identify “sinks” and “sources” in the region.
A “sink” is a habitat to which animals move at a greater rate than the area from where they have dispersed. Conversely, a “source” would be an area from which animals leave to live elsewhere at a greater rate than they come.
The authors of the study were Alyson M. Andreasen, a doctoral candidate from the University of Nevada, Jon P. Beckmann of the Wildlife Conservation Society (WCS), and Matthew L. Forester, William S. Longland and Kelley M. Stewart of the University of Nevada.
Prior to culling data, researchers believed that the mountain lions had a fairly steady eastward movement. The fact that the mountain lion can be hunted in Nevada and not in California led researchers to assume that populations would migrate eastward to take over lands left available after hunters would have killed the native mountain lions.
What they found, however, was quite different. The mountain lions moved in a mostly northern and southerly direction following the topography of the mountain ranges in the region. This resulted in distinctly different genetic populations. East or west directional movement showed that more mountain lions moved west from Central Nevada to the mountains of the Sierra Nevada. The new assumption is that mountain lions migrated to California to take advantage of better habitat quality.
Lead author of the study, Alyson Andreasen, said, “The results are surprising and telling in that in most situations where you have hunting, the animals move in the direction of the resultant vacant territories. While this appears to be occurring in other areas of the state, habitat differences between the Sierra Nevada and the arid Great Basin may be attracting dispersal age mountain lions west into California whereas the abrupt ecotone may act as a barrier for lions residing in the Sierra Nevada.”
An ecotone is a transitional area of vegetation between two different plant communities like a forest and grassland. Ecotones have some of the characteristics of each bordering biological community, but they may also have species not found in the overlapping communities.
The study´s co-author Jon Beckmann stated: “In this case, a hunted population is the source for the non-hunted/protected population. This is somewhat counterintuitive: Some might think that in remote mountainous terrain of Nevada, the impacts of hunting on lion populations would outweigh those associated with more people and roadways in the Sierra of California but this appears to not be the case.
“We predicted we would have more lions coming in from California. We were surprised the Sierra itself was a net importer,” Beckmann continued.
"It may just be more attractive to move into the Sierra Nevada," said Alyson Andreasen, a University of Nevada doctoral student and a lead researcher in the study.
"It's just conjecture at this point, but that's what we think might be going on."
Researchers believe the lusher habitat and greater prey selection of the Sierra region was more attractive than the arid mountains of Nevada.
Populations of mountain lions in the area, according to estimates reported in the San Jose Mercury News, range between 4,000 to 6,000 in California compared to about 3,000 in Nevada.
Following multiple generations, the study has provided information that will be particularly useful when it comes to managing cougar populations and will serve as a launching point for future studies to determine how mountain lions interact with other species and how they select habitat in the region.