Bollens S M, Frost B W
School of Oceanography, University of Washington, WB-10, 98195, Seattle, WA, USA.
Oecologia. 1991 Jul;87(2):155-161. doi: 10.1007/BF00325252.
We present a statistical analysis of a previously published (Yen, 1983) but heretofore unanalyzed data set on the vertical distributions and diel vertical migration (DVM) of adult females of the marine planktonic copepod Euchaeta elongata in Dabob Bay, Washington, USA. Non-ovigerous females were strongly migratory on all four dates sampled, residing between 75-175 m during the day and at shallower depths during the night, commonly entering the upper 50 m of the water column. In contrast, ovigerous females were non-migratory or weakly migratory, largely remaining between 100-175 m both day and night, and entering the upper 50 m of the water column only rarely. Thus non-ovigerous females always migrated much more strongly, as measured by both amplitude of migration and the proportion of animals migrating, than did ovigerous females. These results led us to hypothesize that differential susceptibility to visually orienting predators was the cause of these differences in DVM behavior in female E. elongata, and we subsequently undertook an experimental study of the feeding selectivity of the copepod's natural predator, Pacific herring (Clupea harengus pallasi). Pacific herring exhibited a highly significant preference for ovigerous over nonovigerous adult female E. elongata. The demographic consequences of variable DVM in adult female E. elongata were investigated by way of life table analyses. Results indicated that under conditions of thermal stratification of the water column there is a distinct demographic disadvantage (reduced rate of realized population growth) incurred by non-migratory or weakly migratory ovigerous females due to delayed egg development at cooler subsurface temperatures. We conclude that ovigerous female E. elongata remain at depth both day and night to avoid visually orienting predators, and that such behavior must afford the copepod a demographic advantage of no less than a 26% reduction in adult mortality to offset the demographic cost of delayed egg development.
我们对先前发表的（Yen，1983）但迄今未分析的数据集进行了统计分析，该数据集涉及美国华盛顿州达博湾海洋浮游桡足类长腹水蚤成年雌性的垂直分布和昼夜垂直迁移（DVM）。在所有四个采样日期，未抱卵雌性都具有强烈的迁移性，白天栖息在75 - 175米之间，夜间则处于较浅深度，通常进入水柱上部50米。相比之下，抱卵雌性不迁移或迁移性较弱，白天和夜间大多停留在100 - 175米之间，很少进入水柱上部50米。因此，从未抱卵雌性的迁移幅度和迁移动物的比例衡量，未抱卵雌性的迁移总是比抱卵雌性强烈得多。这些结果使我们推测，对视觉定向捕食者的不同易感性是长腹水蚤雌性DVM行为差异的原因，随后我们对桡足类的天然捕食者太平洋鲱（Clupea harengus pallasi）的摄食选择性进行了实验研究。太平洋鲱对抱卵成年雌性长腹水蚤的偏好远高于未抱卵的成年雌性。通过生命表分析研究了长腹水蚤成年雌性可变DVM的人口统计学后果。结果表明，在水柱热分层的条件下，不迁移或迁移性较弱的抱卵雌性由于在较冷的次表层温度下卵发育延迟，会面临明显的人口统计学劣势（实现的种群增长率降低）。我们得出结论，抱卵长腹水蚤雌性昼夜都停留在深处以躲避视觉定向捕食者，并且这种行为必须为桡足类提供至少26%的成年死亡率降低的人口统计学优势，以抵消卵发育延迟的人口统计学成本。
