Data from: Effective size of density-dependent populations in fluctuating environments

Reliable estimates of effective population size Ne are of central
importance in population genetics and evolutionary biology. For
populations that fluctuate in size, harmonic mean population size is
commonly used as a proxy for (multi-) generational effective size. This
assumes no effects of density dependence on the ratio between effective
and actual population size, which limits its potential application. Here
we introduce density dependence on vital rates in a demographic model of
variance effective size. We derive an expression for the ratio Ne/N in a
density regulated population in a fluctuating environment. We show by
simulations that yearly genetic drift is accurately predicted by our
model, and not proportional to 1/(2N) as assumed by the harmonic mean
model, where N is the total population size of mature individuals. We find
a negative relationship between Ne/N and N. For a given N, the ratio
depends on variance in reproductive success and the degree of resource
limitation acting on the population growth rate. Finally, our model
indicate that environmental stochasticity may affect Ne/N not only through
fluctuations in N, but also for a given N at a given time. Our results
show that estimates of effective population size must include effects of
density dependence and environmental stochasticity.