LTREB Renewal: Experimental tests of alternative states on rocky intertidal shores.

将生态系统从一种类型的群落转变为另一种类型的意外事件，人们知之甚少，但往往会产生严重的生态和经济影响，美国西南部高产草地突然崩溃为沙漠就是一个例子。该项目将调查在缅因湾受保护的岩石海岸上以海藻或贻贝为主的不同群落之间转换的潜在原因。一项独特的长期实验将促进对自然群落对不同规模的生态扰动的恢复力的一般理解，当环境条件恢复时生态过渡是可逆的程度，以及生态群落在受到干扰时的可预测性。研究小组包括一位来自缅因州的高中教师，他长期参与这个项目。每年将有6到8名学生参加实地研究，教师将开发适合高中生和K-12教师的课堂活动。原始数据、试验田全景照片和教育活动将以电子方式提供，调查人员将在YouTube上发布有关数据存档和管理的视频。研究人员将验证以下假设：(1)贻贝床和岩草林的不同群落状态之间的切换是对冬季罕见的大规模冰冲刷的响应；(2)在冰冲刷形成的大片间隙中建立的群落是不可预测的；(3)在重建过程中物种到达的顺序驱动群落发展；(4)替代群落是稳定的。这些假设将使用控制前-控制后-影响（BACI）设计进行测试，该设计包括不同大小的实验清除，1996-97年创建的未清除对照，以及2010-11年再次清除的一半对照。除了收集这些发展中群落演替模式的特征数据外，研究人员还将分析贻贝的捕食率、不同大小贻贝种群的死亡率，以及每年四种关键物种的幼体招募情况。数据分析将比较第一轮实验（1997-2008年）和第二轮实验（2011-2021年）的结果，以检验社区发展是否可预测。重复实验来测试自然生态系统中可选群落状态的方法是独特的，对其他生态系统中可选状态的研究具有广泛的意义。

Unexpected events that tip an ecosystem from one type of community to another are poorly understood yet often have serious ecological and economic effects, exemplified by the sudden collapse of productive grasslands into desert in the southwestern US. This project will investigate the underlying causes of the switch between alternative communities, dominated by either seaweeds or mussels, on sheltered rocky shores in the Gulf of Maine. A unique long-term experiment will advance general understanding of the resilience of natural communities to ecological perturbations of different sizes, the extent to which ecological transitions are reversible when environmental conditions are restored, and the predictability of ecological communities when perturbed. The research team includes a high school teacher from Maine who has a long association with this project. Six to eight of her students will participate in the field research each year, and the teacher will develop classroom activities appropriate for high school students and K-12 teachers. Primary data, panoramic photographs of the experimental plots, and educational activities will be available electronically, and the investigators will post a YouTube video on data archiving and management. The researchers will test hypotheses that (1) switches between alternative community states of mussel beds and rockweed stands occur in response to infrequent, large-scale occurrences of ice scour during winter, (2) the community that becomes established in large clearings made by ice scour is not predictable, (3) the order of species arrival during re-establishment drives community development and (4) the alternative communities are stable. These hypotheses will be tested using a Before-After-Control-Impact (BACI) design consisting of experimental clearings of different sizes, uncleared controls that were created in 1996-97, and half of these controls that were cleared again in 2010-11. In addition to collecting data characterizing patterns of succession in these developing communities, the researchers will assay rates of predation on mussels, mortality rates of mussels in patches of different sizes, and recruitment of juveniles of four key species annually. Analyses of data will compare outcomes from the first run of the experiment (1997-2008) with those from the second run (2011-2021) to test if community development is predictable. The approach of repeating an experiment to test for alternative community states in a natural ecosystem is unique and has broad implications for studies of alternative states in other ecosystems.