A simple demographic explanation for the evolution of the dietary restriction response and its ecological relevance

Considerable life history plasticity is observed in response to variation in food availability and composition. This is perhaps best known in the context of dietary restriction, which consistently induces lower reproduction and higher survival across taxa, with nutritional geometry studies further demonstrating the importance of food composition as well as amount. Although there is a huge amount of mechanistic work on understanding this response, models for how and why this may have evolved are limited and highly debated. Here, we show that a simple demographic model of evolution predicts that the dietary restriction response should evolve as adaptive life history plasticity in a fluctuating environment. This model involves less restrictive assumptions than previous theories, most notably that individuals do not need to return to good resources within their lifetime to gain a benefit from the dietary restriction response. We then explore how this approach might help us to understand and predict life history shifts in response to rapid environment changes in wild populations, and discuss how this perspective affects quantification of individual fitness in wild populations. By considering how population growth maps on the nutritional landscape, a nutritional geometry approach may provide deeper insight into the evolution of this plasticity.