Local extinctions promote co-existence of semelparous and iteroparous lifehistories

We studied the evolution of semelparity (reproducing once per lifetime) and iteroparity (reproducing repeated times in subsequent breeding seasons) us ing numerical simulations. In particular, we were interested in the conditi ons enabling long-term persistence of the two strategies in a given populat ion system. Our general approach was to simulate a semelparous and an itero parous population in a spatially structured system where dispersing individ uals link habitable sub-units together. The local dynamics of each sub-unit was subjected to demographic stochasticity. It appears that demographic st ochasticity and local extinction processes may enhance the long-term co-exi stence of semelparity and iteroparity. The key for co-existence of the two life histories is as follows. First, the population is set into a spatially structured context. Second, demographic stochasticity prevents local popul ation dynamics reaching steady-state equilibria and creates strategy-specif ic local extinctions. These vacancies will be occupied by dispersing indivi duals of semelparous and iteroparous life histories. Without the joint acti on of these elements, the co-existence of the two life histories would beco me impossible.