Before revision:  However, because these models have often very different assumptions , sometimes arbitrary, it is difficult to evaluate what are the real key factors that determine food webs evolution, and whether these models' results are robust or not .
After revision:  However, these models generally make strong arbitrary assumptions on how traits evolve, casting doubts on their robustness. In particular, biomass conversion efficiency is always considered independent of the predator and prey size, which contradicts with the literature .