Consequences of cross-season demographic correlations for population viability

Demographic correlations are pervasive in wildlife populations and can
represent important secondary drivers of population growth. Empirical
evidence suggests that correlations are in general positive for long-lived
species, but little is known about the degree of variation among spatially
segregated populations of the same species in relation to environmental
conditions. We assessed the relative importance of two cross-season
correlations in survival and productivity, for three Atlantic puffin
(Fratercula arctica) populations with contrasting population trajectories
and non-overlapping year-round distributions. The two correlations
reflected either a relationship between adult survival prior to breeding
on productivity or a relationship between productivity and adult survival
in the subsequent year. Demographic rates and their correlations were
estimated with an integrated population model, and their respective
contributions to variation in population growth were calculated using a
transient life table response experiment. For all three populations,
demographic correlations were positive at both time lags, although their
strength differed. Given the difference in year-round distributions of
these populations, this variation in the strength of population-level
demographic correlations points to environmental conditions as an
important driver of demographic variation through life-history
constraints. Consequently, the contributions of variances and correlations
in demographic rates to population growth rates differed among puffin
populations, which has implications for – particularly small –
populations’ viability under environmental change as positive correlations
tend to reduce the stochastic population growth rate.