TDK conference 2015

Living organisms are metabolically active throughout their lives; they take up resources from their environment, convert these resources into useful materials and get rid of leftovers and byproducts. The sum of these reactions and processes is called metabolic activity and we can express its speed by the metabolic rate. Species of various kind exhibit great variability in metabolic rate, regarding both its lifetime mean value and its seasonal changes. Metabolic rate is an important factor in population dynamics, because, by multiplicatively influencing the magnitude of the growth rate, it determines how much an individual experiences the favourable or unfavourable environmental conditions. Considering evolutionary competition, the optimal seasonal metabolic pattern is inevitably affected by the amount of resources and the environmental temperature. This raises the question that, under given environmental conditions in a seasonally changing environment, what the evolutionarily stable metabolic pattern is. To examine this question we used the resource-consumer model of MacArthur as a starting point. We extended this model by introducing a seasonal metabolic activity term and a metabolic cost function, which depends on both environmental temperature and metabolic activity. Using an evolutionary algorithm we examined that, starting from a seasonally constant metabolic activity, what evolutionarily stable metabolic pattern emerges via small evolutionary steps, and how the characteristics of the metabolic pattern are affected by the parameters describing the seasonally changing environment (temperature, resources). Among the many evolutionary outcomes at different parameter combinations, we could distinguish three main categories. Two of them supported the traditional view; in favourable and unfavourable environments higher and lower metabolic rate is beneficial, respectively. The third category represents a counterintuitive, more intricate case; under certain environmental conditions metabolic activity exhibits a positive or negative peak when the seasons change. A positive peak occurs, when a sharply increased metabolic activity, in spite of its costs, accelerates the utilisation of the resources found in suddenly increased amounts at favourable seasonal changes. The negative peak can be explained in a similar way, as a phenomenon observable in case of unfavourable seasonal changes.