Persson A, Hansson L A, Brönmark C, Lundberg P, Pettersson L B, Greenberg L, Nilsson P A, Nyström P, Romare P, Tranvik L
Department of Ecology, Lund University, Ecology Building, S-223 62 Lund, Sweden.
Am Nat. 2001 Jun;157(6):654-69. doi: 10.1086/320620.
Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.
基于捕食者与猎物之间洛特卡 - 沃尔泰拉类型相互作用的简单模型预测，资源增加将对种群产生不稳定影响，并且顶级营养级及以下每隔一个营养级的平衡种群密度都会发生变化。我们在三种水生食物网配置中进行了实验测试，分别施加高营养或低营养添加。通过将系统视为食物链或食物网来构建结果，结果表明营养级生物量随资源增加而增加，这与食物链理论相矛盾。然而，在每个营养级内，食物网配置影响了不同功能组对资源增加的响应程度。通过根据易被捕食程度将营养级划分为功能组，我们能够识别出当系统被视为食物链时被掩盖的显著影响。结果支持了这样的预测，即不易被捕食的猎物可能通过取代其他更易被捕食的猎物来稳定营养级动态。此外，易被捕食的猎物，如水蚤和可食用藻类，其响应符合资源增加悖论假说的预测；也就是说，种群密度的变异性随资源增加而增加。因此，通过将生态系统描述为食物网相互作用的矩阵，并认识到种间竞争和捕食之间的相互作用，与将物种置于不同营养级时相比，我们获得了对生态系统功能更完整的描述。
