Transient dynamics and the evolution of stage-structured life histories

Background/Question/Methods

Life histories tend to be structured by age, size and/or lifestage. Structuring of life histories result in transient responses to demographic disturbance that differ from predictions of long-term increase or decline. We ask, can these transient dynamics influence the evolution of stage structuring in unstable environments? We focus on the adaptive value of demographic inertia, a property of stage structured life histories that can yield faster population growth, or higher fitness, for a given stable rate of increase. We use simple matrix algebra to show that stage-structuring can evolve in response to demographic disturbance. We then use numerical simulations of disturbance regimes, applied to a large database of projection matrix models of plants, to ask whether a) natural populations have a propensity to bounce back from demographic disturbance, and b) whether observed demographic structures are predicted to grow faster than their stable rate of increase.

Results/Conclusions

Algebraic modelling proves that demographic inertia, caused by rare but large disturbance events, promotes the evolution of stage-structured life cycles. Plant populations have a powerfulyl strong propensity to bounce back from random disturbance events. Observed demographic structures of plant populations are predicted to grow faster in the short term, and yield larger population densities in the long term, than predicted by their stable rates of increase. We propose that the adaptive value of demographic inertia in disturbed environments is a key driver of the evolution of stage structured life histories.