Grazing by herbivorous protists contributes to structuring plankton communities through its effect on the growth, biomass, and competitiveness of prey organisms and also impacts the transfer of primary production towards higher trophic levels. Previous evidence shows that heterotrophic processes (grazing rates, g) are more sensitive to temperature than autotrophic ones (phytoplankton growth rates, μ) and also that small cells tend to be more heavily predated than larger ones; however, it remains unresolved how the interplay between changes in temperature and cell size modulates grazing pressure (i.e., g:μ ratio). We addressed this problem by conducting an experiment with four phytoplankton populations, from pico- to microphytoplankton, over a 12 °C gradient and in the presence/absence of a generalist herbivorous protist, Oxyrrhis marina. We found that highest g rates coincided with highest μ rates, which corresponded to intermediate cell sizes. There were no significant differences in either μ or g between the smallest and largest cell sizes considered. The g:μ ratio was largely independent of cell size and C:N ratios, and its thermal dependence was low although species-specific differences were large. We suggest that the similar g:μ found could be the consequence that the energetic demand imposed by rising temperatures would be a more important issue than the mechanical constriction to ingestion derived from prey cell size. Despite the difficulty of quantifying μ and g in natural planktonic communities, we suggest that the g:μ ratio is a key response variable to evaluate thermal sensitivity of food webs because it gives a more integrative view of trophic functioning than both rates separately.

草食性原生生物的放牧通过对猎物生物的生长、生物量和竞争力的影响，有助于构建浮游生物群落，并影响初级生产向更高营养水平的转移。先前的证据表明，异养过程（放牧率，g）比自养过程（浮游植物生长率，μ）对温度更敏感，而且小细胞往往比大细胞更容易被早熟；然而，温度和细胞大小变化之间的相互作用如何调节放牧压力（即g : μ比率）。我们通过对四个浮游植物种群（从微型浮游植物到微型浮游植物）进行了一个实验来解决这个问题，该实验在 12 °C 的梯度下，并且在存在/不存在通才食草原生生物Oxyrrhis marina 的情况下。我们发现最高的g速率与最高的μ速率一致，这对应于中间细胞大小。所考虑的最小和最大单元尺寸之间的μ或g没有显着差异。的克：μ比为很大程度上独立泡孔尺寸和C：N比，并且其热依赖性低虽然物种特异性差异很大。我们建议类似的g: μ发现可能是由于温度升高所施加的能量需求将是比来自猎物细胞大小的摄入机械收缩更重要的问题的结果。尽管难以量化天然浮游生物群落中的μ和g，但我们建议g : μ比率是评估食物网热敏感性的关键响应变量，因为它比单独使用两种比率提供了更综合的营养功能视图。