A tale of two voles: The challenge of the commonness-rarity continuum in conservation planning

摘要

Species rarity is often an important driver of conservation priorities in lieu of greater knowledge of extinction risk. Land management agencies often prioritize management based in part on the commonness of a species, yet identifying what constitutes where a species lies on the commonness-rarity continuum is difficult. Given limited resources, incorrect classification may have detrimental effects on species conservation. In a large area of the Northwest Forest Plan, which guides management of 9.1 million ha of federal forests in the Pacific Northwest, USA, forest management is closely tied to mitigation for the red tree vole (Arborimus longicaudus), a species considered uncommon due in part to its association with older forests. I explore the ability to provide insight into where a species lies along the commonness-rarity continuum by a multi-species comparison. I compared the relative distribution, abundance, and extrinsic conservation threats of red tree voles to western red-backed voles (Myodes californicus), a similar species considered common. Both species occur in younger forests with legacy components of older forests, but reach their greatest densities within older forests. Densities of the two vole species were qualitatively similar. If assignment of a species along a commonness-rarity continuum is a goal of species surveys, their value may be enhanced by including in the survey a set of similar species whose level of rarity is better understood. Although management of the red-tree vole was intended to be guided by adaptive management, challenging policy and legal issues have made that difficu rarity as a criterion for prioritizing management is partly responsible.