Reum Jonathan C P, Holsman Kirstin K, Aydin Kerim Y, Blanchard Julia L, Jennings Simon
School of Aquatic and Fishery Sciences University of Washington Seattle Seattle Washington.
Alaska Fisheries Science Center National Marine Fisheries Service, NOAA Seattle Washington.
Ecol Evol. 2018 Dec 27;9(1):201-211. doi: 10.1002/ece3.4715. eCollection 2019 Jan.
Food web structure and dynamics depend on relationships between body sizes of predators and their prey. Species-based and community-wide estimates of preferred and realized predator-prey mass ratios (PPMR) are required inputs to size-based size spectrum models of marine communities, food webs, and ecosystems. Here, we clarify differences between PPMR definitions in different size spectrum models, in particular differences between PPMR measurements weighting prey abundance in individual predators by biomass ( ) and numbers ( ). We argue that the former weighting generates PPMR as usually conceptualized in equilibrium (static) size spectrum models while the latter usually applies to dynamic models. We use diet information from 170,689 individuals of 34 species of fish in Alaskan marine ecosystems to calculate both PPMR metrics. Using hierarchical models, we examine how explained variance in these metrics changed with predator body size, predator taxonomic resolution, and spatial resolution. In the hierarchical analysis, variance in both metrics emerged primarily at the species level and substantially less variance was associated with other (higher) taxonomic levels or with spatial resolution. This suggests that changes in species composition are the main drivers of community-wide mean PPMR. At all levels of analysis, relationships between weighted mean or weighted mean and predator mass tended to be dome-shaped. Weighted mean values, for species and community-wide, were approximately an order of magnitude higher than weighted mean , reflecting the consistent numeric dominance of small prey in predator diets. As well as increasing understanding of the drivers of variation in PPMR and providing estimates of PPMR in the north Pacific Ocean, our results demonstrate that that or , as well as their corresponding weighted means for any defined group of predators, are not directly substitutable. When developing equilibrium size-based models based on bulk energy flux or comparing PPMR estimates derived from the relationship between body mass and trophic level with those based on diet analysis, weighted mean is a more appropriate measure of PPMR. When calibrating preference PPMR in dynamic size spectrum models then weighted mean will be a more appropriate measure of PPMR.
食物网的结构和动态取决于捕食者与其猎物的体型关系。基于物种和群落范围的首选和实际捕食者 - 猎物质量比（PPMR）估计值是基于体型的海洋群落、食物网和生态系统大小谱模型的必要输入。在此，我们阐明了不同大小谱模型中PPMR定义之间的差异，特别是在通过生物量（ ）和数量（ ）对单个捕食者的猎物丰度进行加权的PPMR测量之间的差异。我们认为，前一种加权方式在平衡（静态）大小谱模型中通常会产生通常概念化的PPMR，而后一种通常适用于动态模型。我们使用来自阿拉斯加海洋生态系统中34种鱼类的170,689个个体的饮食信息来计算这两种PPMR指标。使用层次模型，我们研究了这些指标中的解释方差如何随捕食者体型、捕食者分类分辨率和空间分辨率而变化。在层次分析中，两种指标的方差主要出现在物种水平，与其他（更高）分类水平或空间分辨率相关的方差要少得多。这表明物种组成的变化是群落范围平均PPMR的主要驱动因素。在所有分析层面，加权平均 或加权平均 与捕食者质量之间的关系往往呈圆顶形。物种和群落范围的加权平均 值大约比加权平均 值高一个数量级，这反映了小型猎物在捕食者饮食中始终占主导地位。除了增进对PPMR变化驱动因素的理解并提供北太平洋PPMR的估计值外，我们的结果还表明， 或 以及任何定义的捕食者群体的相应加权平均值都不能直接相互替代。在基于总能量通量开发基于平衡大小的模型或比较从体重与营养级关系得出的PPMR估计值与基于饮食分析得出的估计值时，加权平均 是PPMR的更合适度量。在动态大小谱模型中校准偏好PPMR时，加权平均 将是PPMR的更合适度量。
