Intermittent breeding and constraints on litter size: consequences for effective population size per generation (Ne) and per reproductive cycle (Nb)

In iteroparous species, it is easier to estimate Nb = effective number of breeders in one reproductive cycle than Ne = effective population size per generation. Nb can be used as a proxy for Ne and also can provide crucial insights into eco-evolutionary processes that occur during reproduction. We used analytical and numerical methods to evaluate effects of intermittent breeding and litter/clutch size on inbreeding Nb and Ne. Fixed or random litter sizes ≥ 3 have little effect on either effective-size parameter; however, in species (e.g., many large mammals) in which females can produce only one offspring per cycle, female Nb = ∞ and overall Nb = 4Nb(male). Intermittent breeding reduces the pool of female breeders, which reduces both female and overall Nb; reductions are larger in high-fecundity species with high juvenile mortality and increase when multiple reproductive cycles are skipped. Simulated data for six model species showed that both intermittent breeding and litter-size const...

在多次繁殖物种（iteroparous species）中，估算单次繁殖周期内的有效繁殖数（Nb，effective number of breeders in one reproductive cycle），要比估算每代有效种群大小（Ne，effective population size per generation）更为容易。Nb既可作为Ne的替代指标，也能为繁殖过程中发生的生态进化（eco-evolutionary）过程提供关键见解。我们采用解析法与数值模拟方法，评估了间歇繁殖（intermittent breeding）与窝仔数/产卵量（litter/clutch size）对近交有效繁殖数与近交有效种群大小的影响。当窝仔数固定或随机取值≥3时，对两类有效种群参数几乎无影响；然而在雌性单次繁殖周期仅能产生1个后代的物种（例如多数大型哺乳动物）中，雌性有效繁殖数Nb为无穷大，且总有效繁殖数Nb=4Nb(雄性)。间歇繁殖会缩减雌性繁殖者种群规模，进而降低雌性与整体的有效繁殖数；在幼体死亡率（juvenile mortality）高的高繁殖力（fecundity）物种中，这种缩减效应更为显著，且跳过多次繁殖周期时，缩减效应会进一步增强。针对6个模式物种的模拟数据显示，间歇繁殖与窝仔数……