Evidence for an Allee effect in a declining fur seal population

Allee effects play an important role in the dynamics of many populations and can increase the risk of local extinction. However, some authors have questioned the weight of evidence for Allee effects in wild populations. We therefore exploited a natural experiment provided by two adjacent breeding colonies of contrasting density to investigate the potential for Allee effects in an Antarctic fur seal (Arctocephalus gazella) population that is declining in response to climate-change induced reductions in food availability. Biometric time-series data were collected from 25 pups per colony during two consecutive breeding seasons, the first of which was amongst the worst on record in terms of breeding female numbers, pup birth weights and foraging trip durations. In previous decades when population densities were higher, pup mortality was consistently negatively density-dependent, with rates of trauma and starvation scaling positively with density. However, we found the opposite, with higher ...

阿利效应（Allee effects）在诸多物种种群动态中发挥着关键作用，且会提升局域种群灭绝的风险。然而，部分学者对野生种群中阿利效应的证据可信度提出了质疑。为此，本研究利用两个密度差异显著的相邻繁殖种群所构成的自然实验，针对因气候变化导致食物资源减少而发生种群衰退的南极海狗（Arctocephalus gazella）种群，探究其存在阿利效应的可能性。本研究在两个连续繁殖季中，从每个繁殖种群的25只幼崽处采集生物特征时序数据；其中首个繁殖季的繁殖雌兽数量、幼崽出生体重及觅食行程时长均为有记录以来最差的批次之一。在种群密度更高的过往数十年间，幼崽死亡率始终与密度呈负相关，外伤与饥饿的发生率则随密度升高而正相关增长。然而本研究却得到了相反的结果，即更高的……