(3) Demographic modeling
A traditional SFS-based model recovers a bottleneck in population size,
as expected: the estimated effective population size during the
bottleneck is ~16,000 individuals (1% of the ancestral
population size). However, our demographic model suggests that the
current population size of North American starlings is nearly identical
to its pre-bottleneck size (Supplementary Information). In fact, every
run of the model finds that starlings’ current effective population size
(1.6 million individuals) is considerably higher than the estimated
Ne of the founding population. This model suggests that
starlings experienced rapid population growth after the initial founder
effect, which may contribute to the overall lack of evidence for
inbreeding. We do detect very low levels of inbreeding within some
populations (Table 1, highest FIS = 0.082 in
Washington). Taken together, these models do not suggest a classical
founder effect, whereby effective population size remains very low for
many generations post-bottleneck.