The study and modelling of mechanisms involved in acquisition and use of energy by individuals is vital for estimating their life history traits (e.g. growth, reproductive effort, survival, age and size at maturation), and thus for describing population and community dynamics and quantifying the path between different levels of organisation, i.e. from the individual to the population and ecosystem. What is at stake is to understand how some disturbances related to pollutants, climate, new diseases and parasites or fisheries modify the strategies of energy allocation in aquatic organisms, as well as their life history traits with inferences on population dynamics. Another issue is to investigate the effects of the global change and human activities.

Energy allocation within individual organisms is closely linked to metabolism and depends both on their genotypes [1] and the environment. Organisms exposed to environmental change can respond by different adaptive mechanisms depending on the time scale.  In the short-term, i.e. over shorter timescales than a lifetime, organisms can show rapid and reversible transformations in their physiology, behaviour and morphology, which refer to the principle of phenotypic flexibility [2]. The evolution of organisms represents their long term adaptation to environmental change. Energy allocation strategies with a genetic basis can be modified by the evolutionary process in response to changing environments and probably much more so than the short term adaptive capacities of the same organisms. Such evolutionary changes in energy allocation strategy can have serious long term implications for population dynamics and ecosystems because they have indirect effects on life history traits and trophic fluxes.