Sex-dependent diel vertical migration in northern krill Meganyctiphanes norvegica and its consequences for population dynamics
Sex-dependent diel vertical migration in northern krill Meganyctiphanes norvegica and its consequences for population dynamics
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北方磷虾 Meganyctiphanesnorvegica 的性别依赖性昼夜垂直迁移及其对种群动态的影响
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发表时间：
2003
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通讯作者：
G. Tarling
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作者：
G. Tarling
利用深度离散净采样法和300 kHz声学多普勒海流剖面仪，对克莱德海北部磷虾的垂直迁徙和种群动态进行了研究。磷虾在每一年的采样中都进行了DVM检查。磷虾散射层到达和离开上层的时间分别发生在日落后30分钟和日出前30分钟。雄性和雌性的DVm是不同的，雌性在夜间比同等大小的雄性更接近地表。当幼虫在第一个冬天后成熟成为成虫时，性别比最初是1：1，但随着季节的推移，这一比例变得越来越偏向雄性，以至于到了10月份，这一比例接近3：1。一个基于个体的确定性模型表明，这种偏见可以由雄性和雌性由于DVM而承担的风险的差异来解释。在该模型中，捕食风险是视觉捕食者可获得的光线的函数。同一模型还显示，在夏季，这些DVM的差异导致女性获得的净能量比男性高出40%。女性的预计净能量增长满足了鸡蛋生产的即时能量需求，并提供了剩余，可以抵消未来食物供应的任何下降。该模型没有预测到冬季男性数量的下降幅度大于女性的观察结果。这可能是因为雌性更有能力通过重新吸收富含脂肪的卵巢来应对饥饿。对繁殖所需能量的更大需求似乎正在驱使女性进行比男性更高风险的DVM。这种驱动力很可能是大多数真甲虫物种所共有的。
The diel vertical migration (DVM) and population dynamics of northern krill were investigated in the Clyde Sea over several years using depth-discrete net-sampling and a moored 300 kHz acoustic Doppler current profiler. Krill performed DVM throughout each year of sampling. The respective arrival and departure of the krill scattering layer to and from the upper layers occurred consistently 30 min after sunset and 30 min before sunrise. DVM of males and females was different, with females migrating closer to the surface at night than males of equivalent size. The sex ratio was initially 1:1 when juveniles matured into adults after their first winter, but the ratio became increasingly biased towards males as the season progressed such that, by October, the ratio was close to 3:1. A deterministic individual-based model, in which predation risk was a function of the light available to visual predators, showed that the bias could be accounted for by the difference in risk taken by males and females as a result of their DVMs. The same model also showed that, during summer, the difference in these DVMs resulted in females making a net energy gain that was 40% higher than that of males. The predicted net energy gain for females met the immediate energetic demand for egg production as well as providing a surplus that could offset any future decline in food availability. The model did not predict the observation that the decline in male numbers was greater than that of females over the winter. This may be a result of females being more able to cope with starvation through reabsorption of their lipid-rich ovaries. The greater demand for energy to fuel reproduction appeared to be driving females to undertake a riskier DVM than males. This drive is likely to be common to most euphausiid species.