Data from: Effects of population characteristics and structure on estimates of effective population size in a house sparrow metapopulation

Effective population size (Ne) is a key parameter to understand evolutionary processes and the viability of endangered populations as it determines the rate of genetic drift and inbreeding. Low Ne can lead to inbreeding depression and reduced population adaptability. In this study we estimated contemporary Ne using genetic estimators (LDNE, ONeSAMP, MLNE and CoNe) as well as a demographic estimator in a natural insular house sparrow metapopulation. We investigated whether population characteristics (population size, sex ratio, immigration rate, variance in population size, and population growth rate) explained variation within and among populations in the ratio of effective to census population size (NeNc). In general, NeNc ratios increased with immigration rates. Genetic Ne was much larger than demographic Ne, probably due to a greater effect of immigration on genetic than demographic processes in local populations. Moreover, although estimates of genetic Ne seemed to track Nc quite well, the genetic Ne estimates were often larger than Nc within populations. Estimates of genetic Ne for the metapopulation were however within the expected range (<Nc). Our results suggest that in fragmented populations, even low levels of gene flow may have important consequences for the interpretation of genetic estimates of Ne. Consequently, further studies are needed to understand how Ne estimated in local populations or the total metapopulation relates to actual rates of genetic drift and inbreeding.

有效种群大小（effective population size, Ne）是解析进化过程与濒危种群存续能力的核心参数，因其直接决定了遗传漂变（genetic drift）与近交（inbreeding）的发生速率。低Ne水平会引发近交衰退（inbreeding depression）并降低种群适应性。本研究采用遗传估计器（LDNE、ONeSAMP、MLNE与CoNe）结合人口统计估计器（demographic estimator），对一个自然岛屿家麻雀集合种群（metapopulation）的当代Ne进行了估算。我们探究了种群特征（种群大小、性比、迁入率、种群大小方差与种群增长率）能否解释有效种群大小与普查种群大小之比（Ne/Nc）在种群内部及种群间的变异。总体而言，Ne/Nc比值随迁入率升高而增大。遗传Ne远高于统计Ne，这大概率是因为迁入对局域种群的遗传过程的影响强于对其人口统计过程的影响。此外，尽管遗传Ne的估算值似乎与普查种群大小（Nc）拟合度较好，但多数局域种群的遗传Ne估算值均大于自身的Nc。不过，该集合种群整体的遗传Ne估算值处于预期范围内（小于Nc）。本研究结果表明，在片段化种群中，即便低水平的基因流（gene flow）也可能对遗传Ne估算结果的解读产生重要影响。因此，仍需开展进一步研究以阐明局域种群或整体集合种群的Ne估算值与实际遗传漂变、近交速率之间的关联。