Aquatic Ecology Department, Norwegian Institute for Nature Research P.O. Box 5685 Sluppen, NO-7485, Trondheim, Norway ; University of Jyväskylä, Department of Biological and Environmental Sciences P.O. Box 35, FIN-40014, Jyväskylä, Finland.
Department of Environmental Sciences, University of Helsinki P.O. Box 65, FIN-00014, Helsinki, Finland ; Kilpisjärvi Biological Station, University of Helsinki Käsivarrentie 14622, FIN-99490, Kilpisjärvi, Finland.
Ecol Evol. 2015 Apr;5(8):1664-75. doi: 10.1002/ece3.1464. Epub 2015 Mar 23.
Prey preference of top predators and energy flow across habitat boundaries are of fundamental importance for structure and function of aquatic and terrestrial ecosystems, as they may have strong effects on production, species diversity, and food-web stability. In lakes, littoral and pelagic food-web compartments are typically coupled and controlled by generalist fish top predators. However, the extent and determinants of such coupling remains a topical area of ecological research and is largely unknown in oligotrophic high-latitude lakes. We analyzed food-web structure and resource use by a generalist top predator, the Arctic charr Salvelinus alpinus (L.), in 17 oligotrophic subarctic lakes covering a marked gradient in size (0.5-1084 km(2)) and fish species richness (2-13 species). We expected top predators to shift from littoral to pelagic energy sources with increasing lake size, as the availability of pelagic prey resources and the competition for littoral prey are both likely to be higher in large lakes with multispecies fish communities. We also expected top predators to occupy a higher trophic position in lakes with greater fish species richness due to potential substitution of intermediate consumers (prey fish) and increased piscivory by top predators. Based on stable carbon and nitrogen isotope analyses, the mean reliance of Arctic charr on littoral energy sources showed a significant negative relationship with lake surface area, whereas the mean trophic position of Arctic charr, reflecting the lake food-chain length, increased with fish species richness. These results were supported by stomach contents data demonstrating a shift of Arctic charr from an invertebrate-dominated diet to piscivory on pelagic fish. Our study highlights that, because they determine the main energy source (littoral vs. pelagic) and the trophic position of generalist top predators, ecosystem size and fish diversity are particularly important factors influencing function and structure of food webs in high-latitude lakes.
顶级捕食者的猎物偏好和跨越栖息地边界的能量流动对水生和陆地生态系统的结构和功能至关重要，因为它们可能对生产力、物种多样性和食物网稳定性产生强烈影响。在湖泊中，沿岸和浮游食物网隔室通常是由普通鱼类顶级捕食者耦合和控制的。然而，这种耦合的程度和决定因素仍然是生态研究的一个热门领域，在贫营养的高纬度湖泊中还很大程度上未知。我们分析了普通顶级捕食者北极鲑（Salvelinus alpinus）（L.）在 17 个贫营养的亚北极湖泊中的食物网结构和资源利用，这些湖泊在大小（0.5-1084 km²）和鱼类物种丰富度（2-13 种）方面存在明显的梯度。我们预计，随着大型湖泊中浮游猎物资源的可用性和对沿岸猎物的竞争都可能更高，顶级捕食者将从沿岸能源转向浮游能源，因为大型湖泊中具有多种鱼类群落。我们还预计，由于中间消费者（猎物鱼类）的潜在替代和顶级捕食者的增加的食鱼性，顶级捕食者在鱼类物种丰富度较高的湖泊中占据更高的营养位。基于稳定的碳和氮同位素分析，北极鲑对沿岸能源的平均依赖与湖泊表面积呈显著负相关，而北极鲑的平均营养位，反映了湖泊食物链的长度，随着鱼类物种丰富度的增加而增加。这些结果得到了胃内容物数据的支持，这些数据表明北极鲑从以无脊椎动物为主的饮食转变为对浮游鱼类的食鱼性。我们的研究强调，由于它们决定了主要的能量来源（沿岸与浮游）和普通顶级捕食者的营养位，生态系统大小和鱼类多样性是影响高纬度湖泊食物网功能和结构的特别重要的因素。
