One of the less studied positive interactions among organisms is facilitation. Facilitation may have significant impact on diversity of species especially in low productive environments. We studied the effects of well-known facilitator and ecosystem engineer, the North American beaver (Castor canadensis), on small mammal assemblages in the boreal zone. The small mammals, namely voles, mice, and shrews, were trapped over 2 years in ten beaver-modified habitats and in ten control sites. Contrary to our expectations, we did not observe any differences between species or individual numbers between beaver-modified and control sites. However, there were differences in species composition between sites; grass-eating field voles (Microtus agrestis) and invertebrate-eating shrews (Sorex araneus, Neomys fodiens) tended to be more common in beaver sites while forest-dwelling wood lemmings (Myopus schisticolor) and yellow-necked mice (Apodemus flavicollis) were only captured in control sites. The most common species in both habitats was the bank vole (Myodes glareolus), which is a generalist in its habitat requirements. The bank vole’s population structures were similar between the two habitat types. The actions of beavers in water bodies within boreal forests seem to have no effect on the small mammal diversity and their numbers at the regional scale but may have positive effect on them at the larger landscape level as beavers are increasing the overall habitat diversity in the landscape.

促进作用是生物之间研究较少的积极相互作用之一。便利化可能对物种的多样性产生重大影响，特别是在低产环境中。我们研究了著名的促进者和生态系统工程师北美海狸（Castor canadensis）对北方地区小型哺乳动物组合的影响。这些小型哺乳动物，即田鼠，小鼠和sh，在两年内被困在十个经海狸改造的栖息地和十个控制点中。与我们的预期相反，我们没有观察到海狸修饰位点和对照位点之间物种或个体数量之间的任何差异。但是，地点之间的物种组成存在差异。以草为食的田鼠（Microtus agrestis）和以无脊椎动物为食的sh（Sorex araneus（Neomys fodiens）往往在海狸部位更常见，而居住在森林中的林（Myopus schisticolor）和黄颈小鼠（Apodemus flavicollis）只在对照部位捕获。两种生境中最常见的物种是田鼠（Myodes glareolus），这是对生境要求的通才。在两种栖息地类型之间，河田鼠的种群结构相似。海狸在北方森林水体中的活动似乎对区域内小型哺乳动物多样性及其数量没有影响，但可能会在更大的景观水平上对其产生积极影响，因为海狸正在增加景观中总体生境的多样性。