116-19 Contributions of Juvenile and Adult Life History Diversity for Improving Resilience in Anadromous Salmon Populations
The concept of resilience is often posits the importance of diverse biological assemblages to buffer a system in the face of environmental variation. When the system is a population, scientists often argue that life history diversity spreads risk, thereby protecting a species from stochastic events. These findings have been confirmed in Bristol Bay sockeye salmon, although the extent to which adult and juvenile variation contributes to population buffering remains unknown. We use a stochastic matrix model to test how diversity of life history types during juvenile and adult life stages of salmon influence population dynamics. We test this using four conceptual extremes of a theoretical salmon life cycle, by assuming one or three juvenile life history pathways and one or three adult life histories. We examined these four scenarios using a stochastic model that included variation during both freshwater and marine life stages, run 1000 times to test for extinction thresholds and patterns in productivity. Our analysis indicated that juvenile life history variation increased population growth rate, but that adult life history variation reduced it. However, adult life history variation reduced the variance in population growth rate. These results are compared to emprical patterns in Bristol Bay sockeye salmon.
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