Department of Integrative Biology, Oregon State University, Corvallis, OR 97331;
US Geological Survey, Western Ecological Research Center, Santa Cruz, CA 95060.
Proc Natl Acad Sci U S A. 2022 Feb 22;119(8). doi: 10.1073/pnas.2103483119.
The factors that determine why ecosystems exhibit abrupt shifts in state are of paramount importance for management, conservation, and restoration efforts. Kelp forests are emblematic of such abruptly shifting ecosystems, transitioning from kelp-dominated to urchin-dominated states around the world with increasing frequency, yet the underlying processes and mechanisms that control their dynamics remain unclear. Here, we analyze four decades of data from biannual monitoring around San Nicolas Island, CA, to show that substrate complexity controls both the number of possible (alternative) states and the velocity with which shifts between states occur. The superposition of community dynamics with reconstructions of system stability landscapes reveals that shifts between alternative states at low-complexity sites reflect abrupt, high-velocity events initiated by pulse perturbations that rapidly propel species across dynamically unstable state-space. In contrast, high-complexity sites exhibit a single state of resilient kelp-urchin coexistence. Our analyses suggest that substrate complexity influences both top-down and bottom-up regulatory processes in kelp forests, highlight its influence on kelp-forest stability at both large (island-wide) and small (<10 m) spatial scales, and could be valuable for holistic kelp-forest management.
决定生态系统为何会发生突然状态转变的因素对于管理、保护和恢复工作至关重要。海藻林就是这样一个突然发生转变的生态系统的代表，世界各地的海藻林正越来越频繁地从海藻主导状态转变为海胆主导状态，但控制其动态的潜在过程和机制仍不清楚。在这里，我们分析了来自加利福尼亚州圣尼古拉斯岛附近每两年监测一次的 40 年数据，结果表明，基质复杂性控制着可能存在的（替代）状态的数量以及状态之间转变的速度。群落动态与系统稳定性景观的重建相结合，表明低复杂性地点的替代状态之间的转变反映了由脉冲干扰引发的突然、高速事件，这些事件迅速推动物种跨越动态不稳定的状态空间。相比之下，高复杂性地点则表现出单一的抗逆性海藻-海胆共存状态。我们的分析表明，基质复杂性会影响海藻林中的自上而下和自下而上的调节过程，突出了其对海藻林稳定性的影响，这种影响既体现在大尺度（全岛范围）上，也体现在小尺度（<10 米）上，对于全面的海藻林管理可能具有重要价值。
