Voles of the genus Microtus are major small mammal species responsible for feeding damage to agricultural crops in Europe and North America. Microtus also occupy non-crop habitats such as field margins, hedgerows, edges, riparian zones, set-asides, and fallow fields where the conundrum of “keystone species” vs. “pest species” arises. We ask if montane vole (M. montanus) populations will occupy small set-asides and potentially move into field margins adjacent to tree fruit orchards during periods of high numbers? In replicated sites in south-central British Columbia, Canada, in 2009–2012, we tested the hypotheses (H) that (H₁) small (0.25 ha) perennial grassland sites would be high-quality habitat for voles and generate a multi-annual population fluctuation in abundance; (H₂) voles will follow the same population pattern in set-asides and field margins; and (H₃) voles occurring in set-aside and field margins will disperse into adjacent tree fruit orchards. In set-asides, voles increased to a mean peak population of 290 voles/ha and then declined to 50/ha thereby providing support for H₁. Montane voles generally followed the same pattern of population changes in set-asides and field margins thereby supporting H₂. A much reduced abundance of voles in field margins was likely owing primarily to the areal versus linear extent of the two habitats as both had similar mean abundance of herbs, thatch, and structural diversity. Vegetation management in orchards contributed to very low numbers of voles, and hence no relationship in population pattern with the set-asides. Movement of voles from set-asides to field margins was low and from set-asides and field margins to orchards was almost negligible, thereby providing no support for H₃. There was no feeding damage to crop production during winter periods. Conservation of even small (0.25 ha) set-asides of perennial grasslands may provide high-quality habitat for fluctuating populations of montane voles without necessarily impacting crop production in adjacent orchards that have appropriate vegetation management. Microtus species may be considered keystone architects of biodiversity in at least some agricultural contexts.

田鼠属的田鼠是主要的小型哺乳动物物种，负责破坏欧洲和北美的农作物。Microtus还占据非作物栖息地，例如田地边缘、树篱、边缘、河岸带、休耕地和休耕地，这些地方出现了“关键物种”与“害虫物种”的难题。我们询问山地田鼠（M. montanus）种群是否会在高数量时期占据小空间并可能转移到靠近果园的田地边缘？2009-2012 年，在加拿大不列颠哥伦比亚省中南部的复制站点中，我们检验了假设 (H)，即 (H ₁) 小型（0.25 公顷）多年生草地将成为田鼠的优质栖息地，并产生多年的丰度种群波动；(H ₂ ) 田鼠在留地和田地边缘将遵循相同的种群模式；和 (H ₃ ) 出现在留地和田地边缘的田鼠将分散到相邻的果园中。在留出的时间里，田鼠的平均峰值数量增加到 290 只/公顷，然后下降到 50 只/公顷，从而为 H ₁提供了支持。山地田鼠在留地和田地边缘通常遵循相同的种群变化模式，从而支持 H ₂. 田地边缘田鼠的丰度大幅减少可能主要是由于两个栖息地的面积与线性范围，因为两者的草本、茅草和结构多样性的平均丰度相似。果园中的植被管理导致田鼠数量非常少，因此种群模式与预留没有关系。田鼠从预留地到田地边缘的运动很少，从预留地和田地边缘到果园的运动几乎可以忽略不计，因此没有为 H ₃提供支持. 冬季期间作物生产没有饲料损害。即使是小面积（0.25 公顷）的多年生草地预留地的保护也可以为山地田鼠数量的波动提供高质量的栖息地，而不必影响附近有适当植被管理的果园的作物生产。至少在某些农业环境中，Microtus物种可能被认为是生物多样性的关键建筑师。