Early-life environmental conditions may generate cohort differences in individual
fitness, subsequently affecting population growth rates. Three, nonmutually exclusive
hypotheses predict the nature of these fitness differences: (1) silver spoon effects, where individuals
born in good conditions perform better across the range of adult environments; (2) the
“environmental saturation” hypothesis, where fitness differences only occur in intermediate
adult environmental conditions; and (3) the “environmental matching” or “predictive adaptive
response” (PAR) hypothesis, where fitness is highest when adult environmental conditions
match those experienced in early life. We quantified the context-dependent effect of early-life
environment on subsequent reproductive success, survival, and population growth rate (k) of
Svalbard reindeer, and explored how well it was explained by the three hypotheses. We found
that good early-life conditions increased reproductive success compared to poor early-life conditions,
but only when experiencing intermediate adult environmental conditions. This is the
first example of what appears to be both “beneficial” and “detrimental environmental saturation”
in a natural system. Despite weak early-life effects on survival, cohorts experiencing good
early-life conditions contributed to higher population growth rates, when simulating realistic
variation in adult environmental conditions. Our results show how the combination of a highly
variable environment and biological constraints on fitness components can suppress silver
spoon effects at both extremes of the adult environmental gradient.
beneficial saturation; cohort; delayed environmental effect; detrimental saturation; environmental
matching; fitness; predictive adaptive response; reindeer; silver spoon.
