Environmental variability and semelparity vs. iteroparity as life histories.

Research on the evolution of life histories addresses the topic of fitness trade-offs between semelparity (reproducing once in a lifetime) and iteroparity (repeated reproductive bouts per lifetime). Bulmer (1994) derived the relationship v+P(A)<1 (P(A) is the adult survival;vb(S) and b(S) are the offspring numbers for iteroparous and semelparous breeding strategies, respectively), under which a resident semelparous population cannot be invaded by an iteroparous mutant when the underlying population dynamics are stable. We took Bulmer's population dynamics, and added noise in juvenile and adult survival and in offspring numbers. Long-term coexistence of the two strategies is possible in much of the parameter region ofv +P(A)<1 when noise occurs simultaneously in all three components, or (more restricted) when it affects juvenile and adult survival or adult survival and offspring numbers. Iteroparity cannot persist when the environmental variability involves juvenile survival and offspring numbers, or when the noise acts on the three components separately.