Previous research set off alarm bells by showing that mountain lion populations across California are more different genetically than normal for a wide-roaming predator. New findings published Dec. 3 in Frontiers in Ecology and the Environment have provided an explanation. A team of researchers has found that young mountain lions avoid highly developed areas and crossing busy roads as they navigate between populations seeking breeding territories in the Golden State.
The team tracked 87 "subadult" mountain lions with GPS collars to evaluate their ability to successfully move between different populations. Subadults are mountain lions from about 1 to 3 years old, recently independent of their mothers and trying to make it on their own in a difficult world. Through a process ecologists call "dispersal," they often move large distances seeking natural habitat to establish breeding ranges
"Long-distance dispersal by subadults is the key to maintaining connectivity between different mountain lion populations," said Kyle Dougherty, a postdoctoral researcher at the University of Nebraska–Lincoln and lead author of the study. "When connectivity is disrupted and populations become isolated, it can result in reduced genetic diversity and population decline."
Data from young, dispersing mountain lions is relatively rare. As a result, many studies evaluate connectivity by studying movements of adult, resident animals — which do not typically move between populations.
"Our findings suggest that human infrastructure like roads and development are inhibiting the ability of subadults to move through the landscape, access good habitat and connect populations genetically and demographically," Dougherty said. "All of these things are essentially prerequisites for keeping mountain lion populations healthy at the statewide level."
Isolated populations in southern California and along the central coast exhibit much lower genetic diversity than mountain lion populations in most states. The new research confirms what ecologists suspected previously — that this is likely the result of human infrastructure creating barriers to animal movement. The smallest populations in greater Los Angeles are threatened by local extinction due to isolation by large freeways and development. However, California is also home to larger, genetically diverse mountain lion populations in vast stretches of remote natural habitat, like those in the Sierra Nevada Mountains.
"Ideally, populations in the Sierras and northern California should act as sources of dispersing animals that occasionally bring themselves and their genes to distant populations," said co-author John Benson, associate professor in the School of Natural Resources. "Our work suggests that large roads and extensive development limit the ability of large, healthy populations to maintain smaller, isolated populations as occurs in more natural settings."
The new research is a key piece of the puzzle for conserving mountain lions in California. The species is being considered by state officials for listing under the California Endangered Species Act due to concerns about fractured connectivity, which may threaten the long-term viability of populations in southern California and along the central coast. The team generated a detailed map showing the ease, or difficulty, with which dispersing mountain lions move throughout every portion of the state.
"The map is a direct reflection of the decisions that subadult mountain lions make as they move through the landscape," Benson said. "It highlights critical linkages needed to maintain movement of mountain lions and their genes between populations and will inform conservation strategies to restore connectivity to this fragmented landscape."
Some of the findings provided reason for optimism. Young mountain lions were capable of using even small patches of forest and shrub as "stepping stones" that may allow them to eventually reach larger patches of habitat needed to establish a breeding range. This shows the adaptability of these large cats as they navigate highly fragmented landscapes dominated by humans that lie between remote, rugged tracts of natural habitat in California where mountain lions can thrive.
"Our work supports previous suggestions that mountain lions can traverse inhospitable landscapes as long as there are remnant patches of forest that can act as corridors through urban sprawl," Dougherty said. "However, the ubiquity of freeways and other large roads throughout California presents barriers to movement that may require implementation of wildlife crossing structures to maintain movement of young animals between populations."
The new study helps to identify optimal locations for those structures. The team is currently working on integrating these new results, along with many years of behavioral, mortality, reproductive and genetic data, into a larger effort to understand the statewide population dynamics of mountain lions in California.
The research was a collaborative effort involving researchers from the California Department of Fish and Wildlife; University of California, Davis; University of California, Santa Cruz; National Park Service; True Wild; Institute for Wildlife Studies; All Hands Ecology; Victoria University of Wellington; Integral Ecology Research Center; and University of Nebraska–Lincoln.
