UCLA

Early-life adversity (ELA) can shape survival, reproduction, and fitness long after development, yet wild animals typically encounter multiple ecological, social, and parental challenges whose cumulative consequences remain difficult to quantify. This dissertation develops and applies a cumulative adversity framework to determine how the total burden of ELA affects fitness and life-history outcomes in free-living female yellow-bellied marmots (Marmota flaviventer). Using more than six decades of longitudinal data, I constructed cumulative adversity indices (CAIs) spanning ecological, demographic, and maternal exposures before sexual maturity and evaluated their relationships with survival, lifetime reproductive success, annual breeding probability, and reproductive onset decisions. Cumulative adversity predicted lower pup survival and shorter adult lifespan, whereas indices that allowed favorable conditions to offset adverse experiences performed poorly. Greater adversity was also associated with lower lifetime reproductive success, but this effect was largely explained by reduced lifespan: females with comparable lifespans produced similar numbers of offspring regardless of adversity exposure. Yet, adversity also reduced annual breeding probability and altered age-specific reproductive patterns, indicating trends and costs to reproduction that were not evident from total lifetime output alone. Finally, I found that ELA was associated with contrasting life-history patterns at first reproduction. Greater adversity delayed first reproduction, consistent with developmental or energetic constraints. However, females that began reproducing later after high adversity also weaned larger first litters, suggesting partial compensation through increased initial reproductive investment. Together, these findings show that cumulative ELA primarily constrains fitness by reducing survival and limiting reproductive opportunities. However, shifts in life-history trade-offs that increase early output could mitigate these costs, indicating how other fitness traits can be less constrained and more responsive. Some developmental costs appear irreversible, but individuals may retain limited capacity to adjust reproductive allocation when opportunities arise. A cumulative framework therefore provides a tractable way to connect complex early environments with later-life fitness and may help reshape how environmental risks are evaluated and provide novel avenues for conservation actions.