Strong dependence of demographic stochasticity on a small effective number of breeders in iteroparous species

We provided a theoretical basis for integrating the effective number of breeders ( N b ) into the stochastic dynamics of the number of adults ( N ) for iteroparous species based on individual relationships between adult females and their offspring. Recruitment variation was partitioned into i) parental, ii) nonparental, and iii) environmental processes (including density-dependent effects). The first two processes, summarized by N b , magnified the contribution of the last process to recruitment variation. Assuming that there were no sex differences and an equal sex ratio, the relationship between N b and the factor amplifying recruitment variation when N b / N <0.1 was approximated to provide quantitative guidance for using only N b . For example, N b <42 would have a non-negligible impact on population stochasticity in terms of amplifying the environmental impact by over 5%. The advantage of assessing recruitment variation using N b alone is that only genetic information on samples from the same cohort is sufficient. Thus, the proposed method is applicable in data-limited situations (e.g. endangered species), where there is typically insufficient information on life-history parameters or current age/size structure. The study findings reveal the usefulness of N b in the field of conservation biology and wildlife management.