Maresh Jennifer L, Simmons Samantha E, Crocker Daniel E, McDonald Birgitte I, Williams Terrie M, Costa Daniel P
Department of Ecology & Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
J Exp Biol. 2014 May 1;217(Pt 9):1485-95. doi: 10.1242/jeb.094201.
Widely ranging marine predators often adopt stereotyped, energy-saving behaviours to minimize the energetic cost of transport while maximizing energy gain. Environmental and anthropogenic disturbances can disrupt energy balance by prompting avoidance behaviours that increase transport costs, thereby decreasing foraging efficiency. We examined the ability of 12 free-ranging, juvenile northern elephant seals (Mirounga angustirostris) to mitigate the effects of experimentally increased transport costs by modifying their behaviour and/or energy use in a compensatory manner. Under normal locomotion, elephant seals had low energy requirements (106.5±28.2 kJ kg(-1) day(-1)), approaching or even falling below predictions of basal requirements. Seals responded to a small increase in locomotion costs by spending more time resting between dives (149±44 s) compared with matched control treatments (102±11 s; P<0.01). Despite incurred costs, most other dive and transit behaviours were conserved across treatments, including fixed, rhythmic swimming gaits. Because of this, and because each flipper stroke had a predictable effect on total costs (P<0.001), total energy expenditure was strongly correlated with time spent at sea under both treatments (P<0.0001). These results suggest that transiting elephant seals have a limited capacity to modify their locomotory behaviour without increasing their transport costs. Based on this, we conclude that elephant seals and other ocean predators occupying similar niches may be particularly sensitive to increased transport costs incurred when avoiding unanticipated disturbances.
分布广泛的海洋食肉动物通常会采取刻板的节能行为，以在最大限度提高能量获取的同时，将运输的能量成本降至最低。环境和人为干扰可能会通过引发增加运输成本的回避行为来扰乱能量平衡，从而降低觅食效率。我们研究了12只自由放养的幼年北象海豹（Mirounga angustirostris）通过以补偿方式改变其行为和/或能量使用来减轻实验性增加的运输成本影响的能力。在正常游动时，象海豹的能量需求较低（106.5±28.2千焦/千克·天），接近甚至低于基础需求的预测值。与匹配的对照处理（102±11秒；P<0.01）相比，海豹通过在潜水之间增加休息时间（149±44秒）来应对游动成本的小幅增加。尽管产生了成本，但大多数其他潜水和洄游行为在各处理之间保持不变，包括固定的、有节奏的游泳步态。因此，并且由于每次鳍状肢划水对总成本都有可预测的影响（P<0.001），在两种处理下，总能量消耗与在海上花费的时间都密切相关（P<0.0001）。这些结果表明，洄游中的象海豹在不增加运输成本的情况下改变其运动行为的能力有限。基于此，我们得出结论，象海豹和其他占据相似生态位的海洋食肉动物可能对在避免意外干扰时产生的运输成本增加特别敏感。
