Quantitative measure of fitness in tri-trophic interactions and its influence on diet breadth of insect herbivores

Herbivore-plant interactions should be studied using a tri-trophic approach, but we lack a quantitative measure of the combined effect of top-down and bottom-up forces on herbivore fitness. We propose the combination of the bi-trophic fitness slopes as a tri-trophic fitness measure. We use the relationship between fitness associated with top-down and bottom-up forces and the frequency of host-plant use to calculate the top-down and bottom-up fitness slopes, which we then combine to obtain three possible directions of tri-trophic slopes. A positive tri-trophic slope indicates that herbivores have overall greater tri-trophic fitness on the more frequently used hosts. A null tri-trophic fitness slope indicates that herbivores have similar fitness on all host-plants. A negative tri-trophic slope indicates that herbivores have generally lower fitness on the more frequently used hosts. We tested the explanation power of our method using data from the literature that tested herbivore host shif...植食动物与植物的相互作用（Herbivore-plant interactions）应采用三营养级（tri-trophic）研究方法开展探究，但目前尚缺乏定量测度下行（top-down）与上行（bottom-up）双重作用对植食动物适合度联合效应的手段。我们提出将双营养级（bi-trophic）适合度斜率相结合，作为三营养级适合度测度指标。我们通过关联与下行、上行作用相关的适合度与寄主植物利用频率，计算得到下行、上行适合度斜率，再将二者整合以得到三种可能的三营养级斜率方向：正三营养级斜率表明，植食动物在利用频率更高的寄主植物上整体具备更高的三营养级适合度；零值三营养级适合度斜率表明，植食动物在所有寄主植物上的适合度无显著差异；负三营养级斜率表明，植食动物在利用频率更高的寄主植物上的适合度普遍更低。我们利用已发表文献中针对植食动物寄主转移的数据集，检验了本方法的解释效力……