Marine Predator Unit, Institute of Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tas., 7001, Australia.
J Anim Ecol. 2013 Jan;82(1):72-83. doi: 10.1111/j.1365-2656.2012.02021.x. Epub 2012 Aug 7.
Many optimal foraging models for diving animals examine strategies that maximize time spent in the foraging zone, assuming that prey acquisition increases linearly with search time. Other models have considered the effect of patch quality and predict a net energetic benefit if dives where no prey is encountered early in the dive are abandoned. For deep divers, however, the energetic benefit of giving up is reduced owing to the elevated energy costs associated with descending to physiologically hostile depths, so patch residence time should be invariant. Others consider an asymptotic gain function where the decision to leave a patch is driven by patch-depletion effects - the marginal value theorem. As predator behaviour is increasingly being used as an index of marine resource density and distribution, it is important to understand the nature of this gain function. We investigated the dive behaviour of the world's deepest-diving seal, the southern elephant seal Mirounga leonina, in response to patch quality. Testing these models has largely been limited to controlled experiments on captive animals. By integrating in situ measurements of the seal's relative lipid content obtained from drift rate data (a measure of foraging success) with area-restricted search behaviour identified from first-passage time analysis, we identified regions of high- and low-quality patches. Dive durations and bottom times were not invariant and did not increase in regions of high quality; rather, both were longer when patches were of relatively low quality. This is consistent with the predictions of the marginal value theorem and provides support for a nonlinear relationship between search time and prey acquisition. We also found higher descent and ascent rates in high-quality patches suggesting that seals minimized travel time to the foraging patch when quality was high; however, this was not achieved by increasing speed or dive angle. Relative body lipid content was an important predictor of dive behaviour. Seals did not schedule their diving to maximize time spent in the foraging zone in higher-quality patches, challenging the widely held view that maximizing time in the foraging zone translates to greater foraging success.
许多针对潜水动物的最优觅食模型都考察了最大化觅食区停留时间的策略，这些模型假设猎物获取量随搜索时间线性增加。其他模型则考虑了斑块质量的影响，并预测如果潜水者在潜水初期没有遇到猎物就放弃潜水，那么从能量角度来看是有益的。然而，对于深潜动物来说，由于与下降到生理上不利的深度相关的能量成本增加，放弃潜水的能量收益会减少，因此斑块停留时间应该不变。其他模型则考虑了一种渐近收益函数，其中离开斑块的决策是由斑块耗竭效应驱动的——边际价值定理。由于捕食者行为越来越被用作海洋资源密度和分布的指标，因此了解这种收益函数的性质非常重要。我们研究了世界上最深的潜水海豹——南方象海豹 Mirounga leonina 对斑块质量的潜水行为。这些模型的测试主要限于对圈养动物的受控实验。通过将从漂移率数据（衡量觅食成功的指标）中获得的海豹相对脂质含量的原位测量值与从首次通过时间分析中识别出的区域限制搜索行为相结合，我们确定了高质量和低质量斑块的区域。潜水持续时间和底部时间并不不变，在高质量区域内没有增加；相反，当斑块质量相对较低时，两者都会更长。这与边际价值定理的预测一致，并为搜索时间与猎物获取之间的非线性关系提供了支持。我们还发现高质量斑块中的下降和上升速度更高，这表明当斑块质量较高时，海豹会尽量减少前往觅食区的旅行时间；然而，这并不是通过增加速度或潜水角度来实现的。相对体脂含量是潜水行为的重要预测指标。海豹并没有安排潜水以最大化在高质量斑块中的停留时间，这挑战了广泛存在的观点，即最大化在觅食区的停留时间会转化为更大的觅食成功。
