Foraging theory improves our understanding of food web in many ways. As to the food-web structure, there are at least two major aspects food-web ecology can take from foraging theory. On the one hand, on the basis of optimal diet choice or patch choice, foraging theory predicts resource use by a consumer and thus the static structure of food web at a particular moment. On the other hand, the adaptive diet shift makes interaction strength temporally variable and thus predicts non-static food-web structure. In this talk, I show that these two aspects, one dynamic and one static, taken together may allow us to understand the response of food-web structure to environmental gradients. Food-chain length, the number of feeding links from the basal species to the top species, is a central characteristic of ecological communities. Although empirical studies suggest its correlation, or non-correlation, with some environmental factors, there is still no mechanistic explanation for those patterns. Analysis of “adaptive food web” model shows that those patterns in food-chain length emerge from interaction among multiple adaptive predators. The dynamic models of interacting adaptive predators reproduce the frequently reported pattern that food-chain length increases with species richness, while not being influenced by ecosystem productivity. Further, the model predicts that in simpler communities or without adaptive diet choice, in contrast, food-chain length increases with increasing productivity, as observed in experimental microcosms.