Gray wolves are a premier example of how predators can transform ecosystems through trophic cascades. However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned. We demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. Beavers are ecosystem engineers that generate most wetland creation throughout boreal ecosystems. By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers.

灰狼是捕食者如何通过营养级联改变生态系统的首要例子。然而，狼是否会像之前所说的那样剧烈地改变生态系统，这一点越来越受到质疑。我们展示了狼如何通过杀死分散的海狸来改变湿地的形成和重新殖民化。海狸是生态系统工程师，它们在整个北方生态系统中创造了大多数湿地。通过研究海狸池塘的创建和重新定殖模式以及狼对海狸的捕食，我们确定 84% 的新创建和重新定殖的海狸池塘一直被占用直到秋天，而 0% 的新创建和重新定殖的池塘在被狼杀死后仍然活跃殖民那个池塘的海狸。通过影响海狸设计生态系统的地点和时间，狼改变了所有的生态过程（例如，由于海狸造成的蓄水池而发生的蓄水、养分循环和森林演替）。我们的研究展示了捕食者在杀死生态系统工程师时如何对生态系统产生巨大影响。