Virginia Institute of Marine Science, Gloucester Point, VA, 23062-1346, USA.
Tennenbaum Marine Observatories Network, Smithsonian Institution, Washington, D.C., 20013-7012, USA.
Ecol Lett. 2015 Jul;18(7):696-705. doi: 10.1111/ele.12448. Epub 2015 May 17.
Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.
营养污染和放牧减少都可以刺激藻类大量繁殖，这已经在大量实验中得到证实。但是，由于实验很少将环境因素和生物多样性的自然变化纳入其中，因此，确定自上而下和自下而上的驱动力相对强度的条件仍未得到解决。我们在海洋基础物种鳗草（Zostera marina）的分布范围内的 15 个地点进行了养分添加和放牧减少的因子实验，以量化自上而下和自下而上的控制如何与生物多样性和环境驱动力的自然梯度相互作用。实验证实了对藻类的适度的自上而下的控制，而施肥通常没有效果。出乎意料的是，食草动物和藻类生物量的变化更多地受到跨站点食草动物和鳗草多样性的变化的预测，而不是受到全球环境梯度的影响。此外，这些大规模的模式与先前的小规模实验惊人地吻合。我们的研究结果将全球和地方的证据联系起来，表明生物多样性和自上而下的控制强烈影响受威胁的海草生态系统的功能，并且表明生物多样性与全球变化的压力因素同样重要。
