Seasonal timing of ecosystem linkage mediates life-history variation in a salmonid fish population

Life-history variation can contribute to the long-term persistence of populations; however, it remains unclear which environmental factors drive life-history variation within a population. Seasonally recurring resource subsidies are common in nature and may influence variations in recipient consumers' life-history traits. In this study, we experimentally demonstrated that terrestrial invertebrate subsidies occurring early in the growing season facilitated consumer individuals to adopt fast growth. In contrast, fewer consumer individuals adopted fast growth when subsidies occurred late in the growing season. Consumer individuals that adopted fast growth matured early at age 1, suggesting that the observed variation in life history emerged along with a fast-slow life-history continuum. The estimated survival probability was lower in consumer individuals from the faster growth cluster in the no-supply treatment (control), suggesting a growth-survival trade-off. However, the growth-survival trade-off became unclear in the early-supply treatment and even reversed in the late-supply treatment. As a result, the frequency of consumer individuals maturing at age 1 was higher in the early-supply treatment than in the late-supply treatment and no-supply treatment, implying a higher short-term population growth with the early subsidies. Our findings highlight that seasonal ecosystem linkages through resource subsidies help us understand how life-history variation can be maintained within a population at the landscape scale.