Institute of Ecology, College of Urban and Environmental Science, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, China.
EcoNetLab, German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.
J Anim Ecol. 2021 Jun;90(6):1444-1454. doi: 10.1111/1365-2656.13464. Epub 2021 Mar 19.
Food webs capture the trophic relationships and energy fluxes between species, which has fundamental impacts on ecosystem functioning and stability. Within a food web, the energy flux distribution between a predator and its prey species is shaped by food quantity-quality trade-offs and the contiguity of foraging. But the distribution of energy fluxes among prey species as well as its drivers and implications remain unclear. Here we used 157 aquatic food webs, which contain explicit energy flux information, to examine whether a predator's foraging is asymmetric and biased towards lower or higher trophic levels, and how these patterns may change with trophic level. We also evaluate how traditional topology-based approaches may over- or under-estimate a predator's trophic level and omnivory by ignoring the asymmetric foraging patterns. Our results demonstrated the prevalence of asymmetric foraging in natural aquatic food webs. Although predators prefer prey at higher trophic levels with potentially higher food quality, they obtain their energy mostly from lower trophic levels with a higher food quantity. Both tendencies, that is, stronger feeding preference for prey at higher trophic levels and stronger energetic reliance on prey at lower trophic levels are alleviated for predators at higher trophic levels. The asymmetric foraging lowers trophic levels and omnivory at both species and food web levels, compared to estimates from traditional topology-based approaches. Such overestimations by topology-based approaches are most pronounced for predators at lower trophic levels and communities with higher number of trophic species. Our study highlights the importance of energy flux information in understanding the foraging behaviour of predators as well as the structural complexity of natural food webs. The increasing availability of flux-based food web data will thus provide new opportunities to reconcile food web structure, functioning and stability.
食物网捕捉物种之间的营养关系和能量流动，这对生态系统功能和稳定性具有根本影响。在食物网中，捕食者与其猎物之间的能量流动分布受到食物数量-质量权衡和觅食连续性的影响。但是，猎物物种之间的能量流动分布及其驱动因素和影响仍然不清楚。在这里，我们使用了 157 个包含明确能量通量信息的水生食物网，以检验捕食者的觅食是否不对称且偏向于较低或较高的营养级，以及这些模式如何随营养级而变化。我们还评估了传统基于拓扑的方法如何通过忽略不对称的觅食模式而高估或低估捕食者的营养级和杂食性。我们的结果表明，不对称觅食在自然水生食物网中很普遍。尽管捕食者更喜欢具有更高食物质量的较高营养级的猎物，但它们主要从具有更高食物数量的较低营养级获得能量。这两种趋势，即对较高营养级的猎物更强的摄食偏好和对较低营养级的猎物更强的能量依赖，在较高营养级的捕食者中都得到缓解。与基于传统拓扑的方法的估计相比，不对称觅食降低了物种和食物网层面的营养级和杂食性。基于拓扑的方法的这种高估在营养级较低的捕食者和具有较高营养物种数量的群落中最为明显。我们的研究强调了在理解捕食者的觅食行为以及自然食物网的结构复杂性方面，能量通量信息的重要性。基于通量的食物网数据的日益普及将为协调食物网结构、功能和稳定性提供新的机会。
