Seasonal timing of ecosystem linkage contributes to maintaining life-history variation in a salmonid fish population

Life-history variation can contribute to long-term persistence of populations, but it remains unknown what ecosystem properties maintain life-history variation within a population. Seasonally recurring resource subsidies are common in nature, but human-induced environmental changes, including global climate change, are causing temporal shifts and decline in those subsidies. We experimentally demonstrated that the terrestrial invertebrate subsidy occurring early in a growing season facilitated red-spotted masu salmon individuals to adopt a fast life, while the early-subsidy also maintained individuals that adopted a slow life. In contrast, the late-subsidy did not increase the fast-life individuals as much as the early-subsidy did. Consequently, the life-history variation was higher in the early-subsidy treatment than in late-subsidy treatment and no-subsidy control. The variation in life-history was not simply explained by the growth-survival trade-off. These results highlight the role of seasonal ecosystem linkages in maintaining life-history variation within a population and securing population stability at land-scape scale.