Study: Black bears returning to Great Basin
November 26, 2017
A new study finds that conservation efforts have resulted in successful re-colonization of black bears into portions of their historic ranges in Nevada's Great Basin. The animals had been absent from some of these areas for more than 80 years.
The Wildlife Conservation Society and Nevada Department of Wildlife teamed with the University of Nevada, Reno, to use hair and blood samples from bears to examine the genetic consequences of this natural recolonization in a large-bodied mammal, and this is one of the few empirical examples to do so.
While unregulated hunting and conflicts with settlers' domestic livestock contributed to the bear's local extinction, also known as extirpation, from the Great Basin in the early 1900s, landscape changes due to clear-cutting of forests throughout western and central Nevada during the settlement era likely played an important role as well. But as fossil fuel replaced timber as a heat and energy source, forestry and grazing practices evolved, and reforestation and habitat regeneration occurred in parts of the black bear's former range.
In addition to habitat regeneration, the study authors attribute the successful recolonization to conservation efforts conducted by WCS and NDOW over the course of more than 20 years. These included public education, investing in bear-proofing communities, reducing conflict rates between carnivores and people, and reduced human-caused carnivore mortality rates.
As a result of the efforts, a once negative population growth rate for bears in more-populated areas became an average annual growth rate of 16 percent for more than a decade, and re-colonization of historic ranges in the mountains of the Great Basin ensued. More than 500 black bears have now recolonized these areas.
In addition to the demographics of the recovery, the scientists studied the impacts of this loss and subsequent recovery on the genetic makeup of the population.
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Genetic analysis demonstrated that the population has indeed undergone an extirpation followed by a re-expansion. The re-colonizing bears originated from a source population in the Sierra-Nevada Mountains and expanded in a west-to-east pattern back into the Great Basin.
"This study represents a great partnership between wildlife management and geneticists," said Jason Malaney, lead author of the genetic study. "Wildlife managers deploy long-term field-surveys of black bears, collect tissue samples along the way,that are then used to better understand the complexities of re-colonization. This results in improved management outcomes."
The authors of the study conclude that based on their results, black bears in the western Great Basin appear to currently maintain levels of connectivity between various mountain ranges that are sufficient to prevent genetic bottlenecks following recolonization. Further, black bears in the western Great Basin best represent a genetic metapopulation (a group of populations separated but of the same species with individuals that interact with other populations).
Finally, they note that as the human-footprint expands over time in the region, this level of genetic connection among various mountain ranges may not last without conservation efforts to maintain connectivity.
"The recovery of large carnivores is relatively rare globally yet this is the goal of conservation," said WCS conservation scientist Jon Beckmann. "Understanding the mode of recolonization and its genetic consequences is of broad interest in ecology and critical to successful conservation programs."
"Natural rewilding of the Great Basin: genetic consequences of colonization by black bears (Ursus americanus)" appears in the current edition of Diversity and Distributions.
Co-authors include: Jason Malaney of UNR; Carl Lackey of NDOW; Jon Beckmann of the WCS; and Marjorie Matocq of UNR.
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