Does evolution of iteroparous and semelparous reproduction call for spatially structured systems?

A persistent question in the evolution of life histories is the fitness tra de-off between reproducing only once (semelparity) in a lifetime or reprodu cing repeated times in different seasons (iteroparity). The problem can be formulated into a research agenda by assuming that one reproductive strateg y is resident (has already evolved) and by asking whether invasion (evoluti on) of an alternative reproductive strategy is possible. For a spatially no nstructured system, Bulmer (1994) derived the relationship nu + P-A < 1 (P- A is adult survival; nu b(S) and b(S) are offspring numbers for iteroparous and semelparous breeding strategies, respectively) at which semelparous po pulation cannot be invaded by an iteroparous mutant. When the inequality is changed to nu + P-A > 1, invasion of a semelparous mutant is not possible. From the inequalities, it is easy to see that possibilities for evolutiona ry establishment of a novel reproductive strategy are rather narrow. We ext ended the evolutionary scenario into a spatially structured system with dis persal linkage among the subunits. In this domain, a rare reproductive stra tegy can easily invade a population dominated by a resident reproductive st rategy. The parameter space enabling invasion is far more generous with spa tially structured evolutionary scenarios than in a spatially nonstructured system.