Marine Science Institute, University of California, Santa Barbara, California, 93106, USA.
Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, 22904, USA.
Ecology. 2018 Nov;99(11):2442-2454. doi: 10.1002/ecy.2485. Epub 2018 Oct 30.
Disturbances often cause the disproportionate loss of foundation species but understanding how the frequency and severity of disturbance to such organisms influence biological communities remains unresolved. This gap in knowledge exists in part because of the rarity of ecologically meaningful studies capable of disentangling different elements of disturbance. Hence, we carried out a long-term (9 yr), large-scale (2,000 m plots), spatially replicated (4 sites) field experiment in which we manipulated disturbance to a globally distributed marine foundation species, the giant kelp Macrocystis pyrifera, and tracked community responses over time. To distinguish the effects of disturbance frequency and severity on the biodiversity and composition of temperate rocky reef communities, we simulated the repeated loss of giant kelp from destructive winter waves across a background of natural variation in disturbance. By following the response of over 200 taxa from the surrounding community, we discovered that the frequency of disturbance to giant kelp changed the biomass, diversity, and composition of community guilds in a manner commensurate with their dependence on the physical (i.e., benthic light and space), trophic (i.e., living and detrital biomass), and habitat (i.e., biogenic structure) resources mediated by this foundation species. Annual winter disturbance to giant kelp reduced living and detrital giant kelp biomass by 57% and 40%, respectively, enhanced bottom light by 22%, and halved the seafloor area covered by giant kelp holdfasts. Concomitantly, the biomass of understory algae and epilithic sessile invertebrates more than doubled, while the biomass of rock-boring clams, mobile invertebrates, and fishes decreased 30-61%. Frequent loss of giant kelp boosted understory algal richness by 82% and lowered sessile invertebrate richness by 13% but did not affect the biodiversity of mobile fauna. In contrast to changes driven by disturbance frequency, interannual variation in the severity of disturbance to giant kelp had weaker, less consistent effects, causing only modest changes in assemblages of sessile invertebrates, mobile invertebrate herbivores, and fishes. Our results broaden the foundation species concept by demonstrating that repeated disturbance to a dominant habitat-forming species can outweigh the influence of less frequent but severe disturbances for the surrounding community.
干扰常常导致基础物种不成比例的丧失，但对于干扰这些生物的频率和严重程度如何影响生物群落，人们的理解仍未得到解决。这种知识上的差距部分是由于缺乏具有生态学意义的研究，这些研究能够理清干扰的不同要素。因此，我们进行了一项长期（9 年）、大规模（2000 米的样地）、空间复制（4 个地点）的野外实验，在这个实验中，我们对一种分布广泛的海洋基础物种——巨藻（Macrocystis pyrifera）进行了干扰处理，并跟踪了随时间推移的群落响应。为了区分干扰频率和严重程度对温带岩石礁群落生物多样性和组成的影响，我们在自然干扰背景下，模拟了破坏性冬季海浪对巨藻的反复损失。通过跟踪周围群落中 200 多个类群的反应，我们发现，巨藻受干扰的频率改变了社区群组成分的生物量、多样性和组成，这与它们对物理（即，底栖光和空间）、营养（即，活体和碎屑生物量）和栖息地（即，生物成因结构）资源的依赖程度相一致，而这些资源是由该基础物种提供的。每年冬季对巨藻的干扰分别减少了活体和碎屑巨藻的生物量 57%和 40%，增加了底层光照 22%，并将巨藻固着器占据的海底面积减少了一半。与此同时，亚层藻类和附生固着无脊椎动物的生物量增加了一倍以上，而钻孔贝类、移动无脊椎动物和鱼类的生物量减少了 30-61%。巨藻频繁的损失使亚层藻类的丰富度增加了 82%，使附生无脊椎动物的丰富度降低了 13%，但对移动动物区系的生物多样性没有影响。与受干扰频率驱动的变化相比，巨藻受干扰严重程度的年际变化的影响较弱，一致性也较差，仅对附生无脊椎动物、移动无脊椎动物草食者和鱼类的群落组成产生适度影响。我们的研究结果拓宽了基础物种的概念，证明了对主要生境形成物种的反复干扰可能超过对周围群落的影响较小但更频繁的干扰。
