Spatiotemporal relationship between adult census size and genetic population size across a wide population size gradient

Adult census population size (N) and effective number of breeders (Nb) are highly relevant for designing effective conservation strategies. Both parameters are often challenging to quantify, however, making it of interest to determine whether one parameter can be generalized from the other. Yet, the spatiotemporal relationship between N and Nb has not been well characterized empirically in many taxa. We analysed this relationship for 5–7 consecutive years in twelve brook trout populations varying greatly in N (49-10032) and Nb (3-567) and identified major environmental variables affecting the two parameters. N or habitat size alone explained 47–57% of the variance in Nb, and Nb was strongly correlated with effective population size. The ratio Nb/N ranged from 0.01 to 0.45 and increased at small N or following an annual decrease in N, suggesting density-dependent constraints on Nb. We found no evidence for a consistent, directional difference between variability in Nb and/or Nb/N among s...