Abstract
Individuals differ greatly in their life courses, but how such diversity is generated, how it has evolved and how it is maintained is less understood. However, such understanding is crucial to comprehend evolutionary and ecological population dynamics. In structured populations individuals diversify by transitioning through discrete stages that end with death. Such stage transitions can be described by a Markov chain, and the rate of diversification of these stage-sequences individuals experience with increasing age can be quantified by the population entropy of a Markov chain. Here, we derive sensitivities of the population entropy of a Markov chain in order to identify which transitions are generating most diversification among life courses, i.e. what drives diversification. We then use these derived sensitivities to reveal potential selective forces on the dynamics of life courses. We illustrate our exact result for the sensitivity of the entropy using an example on a seabird population that is structured by reproductive stages. In our example on the murres, the most important drivers of diversification of life courses are not linked to the most sensitive transitions influencing population growth, which suggests that observed diversification in life courses are rather neutral than adaptive. However, this interpretation has to approached with caution since we only explored one of many solutions for the constraints among transition probabilities. We believe to only start to understand how individual level dynamics shape population level evolutionary and ecological dynamics, and many more exciting discoveries await us in exploring underlying dynamics of age- and stage-structured populations.