Figure 3.

Warming impacts on predator–prey food chains depend on within-species variation (here individual variation in predation risk). Food chain models that (a) ignore within-species variation predict that warming will lead to gradual declines in top-predators and intermediate consumers (as well as resources, when these are also directly impacted by temperature), whereas a model that (b) accounts for within-species variation in size and corresponding vulnerability to predation in intermediate consumers, demonstrates that warming can lead to alternative stable states in the food chain and sudden predator collapses. In both cases, warming weakens top-down control owing to bottom-up effects of declining resources and a stronger warming-induced decrease in net energy gain of top-predators than of their prey, the intermediate consumer. However, when predation is size-dependent (b), weakened top-down control with warming can instead lead to a decrease in the prey that is vulnerable to predation (in b: small life-stage of the intermediate consumer), and collapse of top-predator populations owing to a lack of prey (right-most food web illustration in b). (Online version in colour.)