Langendorf Ryan E, Estes James A, Watson Jane C, Kenner Michael C, Hatfield Brian B, Tinker M Tim, Waddle Ellen, DeMarche Megan L, Doak Daniel F
Department of Environmental Studies, University of Colorado, Boulder, CO 80309.
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309.
Proc Natl Acad Sci U S A. 2025 Mar 11;122(10):e2413360122. doi: 10.1073/pnas.2413360122. Epub 2025 Mar 3.
Sea otters are an iconic keystone predator that can maintain kelp forests by preying on grazing invertebrates such as sea urchins. However, the effects of sea otters on kelp forests vary over their geographic range. Here, we analyze two 30-y datasets on kelp forest communities during the reintroduction of sea otters along the west coast of Vancouver Island, BC, Canada, and around San Nicolas Island, CA. We developed a community model to estimate species interactions as dynamic rates, varying with community state. We find evidence of a classic trophic cascade off Vancouver Island; the arrival of otters quickly led to depletion of urchins and recovery of kelp. However, this cascade was muted around San Nicolas Island, with otters, urchins, and kelp all coexisting at intermediate densities for multiple years. Our models show that this difference came from a pulse of strong otter impacts on urchins following recolonization off Vancouver Island, but not off San Nicolas Island. The mean effects of otters on urchins and urchins on kelp were not stronger in the north, indicating that interaction dynamics and not average interaction strength are key to explaining differences in community trajectories. We also find stronger multistep interaction chains in the south, arising from competitive interactions that indirectly buffered otter effects. These findings shed light on long-standing hypotheses about how interspecific interactions can alter the function of keystone species across community contexts. More broadly, we show how community change can be more accurately predicted by considering dynamic interaction strengths.
海獭是一种标志性的关键捕食者，它可以通过捕食诸如海胆等食草性无脊椎动物来维持海带森林。然而，海獭对海带森林的影响在其地理分布范围内有所不同。在这里，我们分析了两个30年的数据集，这些数据集是关于在加拿大不列颠哥伦比亚省温哥华岛西海岸以及加利福尼亚州圣尼古拉斯岛周围重新引入海獭期间海带森林群落的数据。我们开发了一个群落模型，以估计物种间的相互作用，将其作为随群落状态变化的动态速率。我们发现温哥华岛外存在经典营养级联的证据；海獭的到来迅速导致海胆数量减少，海带得以恢复。然而，这种级联效应在圣尼古拉斯岛周围并不明显，海獭、海胆和海带多年来一直以中等密度共存。我们的模型表明，这种差异源于温哥华岛重新定殖后海獭对海胆的强烈脉冲式影响，而圣尼古拉斯岛没有这种情况。海獭对海胆以及海胆对海带的平均影响在北部并不更强，这表明相互作用动态而非平均相互作用强度是解释群落轨迹差异的关键。我们还发现南部存在更强的多步相互作用链，这是由间接缓冲海獭影响的竞争相互作用产生的。这些发现揭示了关于种间相互作用如何在不同群落背景下改变关键物种功能的长期假设。更广泛地说，我们展示了通过考虑动态相互作用强度可以更准确地预测群落变化。
