Data from: The effect of demographic correlations on the stochastic population dynamics of perennial plants

Understanding the influence of environmental variability on population
dynamics is a fundamental goal of ecology. Theory suggests that, for
populations in variable environments, temporal correlations between
demographic vital rates (e.g., growth, survival, reproduction) can
increase (if positive) or decrease (if negative) the variability of
year-to-year population growth. Because this variability generally
decreases long-term population viability, vital rate correlations may
importantly affect population dynamics in stochastic environments. Despite
long-standing theoretical interest, it is unclear whether vital rate
correlations are common in nature, whether their directions are
predominantly negative or positive, and whether they are of sufficient
magnitude to warrant broad consideration in studies of stochastic
population dynamics. We used long-term demographic data for three
perennial plant species, hierarchical Bayesian parameterization of
population projection models, and stochastic simulations to address the
following questions: (1) What are the sign, magnitude, and uncertainty of
temporal correlations between vital rates? (2) How do specific pairwise
correlations affect the year-to-year variability of population growth? (3)
Does the net effect of all vital rate correlations increase or decrease
year-to-year variability? (4) What is the net effect of vital rate
correlations on the long-term stochastic population growth rate (λS)? We
found only four moderate to strong correlations, both positive and
negative in sign, across all species and vital rate pairs; otherwise,
correlations were generally weak in magnitude and variable in sign. The
net effect of vital rate correlations ranged from a slight decrease to an
increase in the year-to-year variability of population growth, with
average changes in variance ranging from -1% to +22%. However, vital rate
correlations caused virtually no change in the estimates of λS (mean
effects ranging from -0.01% to +0.17%). Therefore, the proportional
changes in the variance of population growth caused by demographic
correlations were too small on an absolute scale to importantly affect
population growth and viability. We conclude that in our three focal
populations and perhaps more generally, vital rate correlations have
little effect on stochastic population dynamics. This may be good news for
population ecologists, because estimating vital rate correlations and
incorporating them into population models can be data-intensive and
technically challenging.