Encyclopedia of Marine Mammals
Encyclopedia of Marine Mammals
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DOI：
10.5860/choice.40-0656
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发表时间：
2017
期刊：
影响因子：
2.6
通讯作者：
P.;Costa
中科院分区：
文献类型：
--
作者：
P.;Costa
能量获取和分配的测量可以定量评估动物如何组织日常或季节性活动，以及它们如何优先考虑其行为以最大限度地提高健康水平。什么以食物形式进入，以生长、繁殖、修复、废物或代谢功形式排出，可以通过能量流模型来描述（图 1）。至少，生存要求个人在能源成本和收益方面实现收支平衡，平衡自我维持的成本与获得的能源的成本。为了生长和繁殖，动物必须获得比生存所需更多的能量，这样它们才能处于正能量平衡。许多海洋哺乳动物经历能量平衡的变化，在高生产力环境中进食时获得能量，然后在迁徙或繁殖期间禁食。能量获取和消耗之间的这种平衡，以及实现这种平衡的时间和空间尺度，在物种和环境之间存在显着差异。对于某些物种，包括海獭、海狮和海狗，高能量消耗率是通过高能量获取率来满足的（Costa 和 Williams，2000）。这些动物优先生活在食物丰富的近岸环境或上升流区域（Costa，1993），在较小（数十至数百公里）、更直接（每日至每周）尺度上找到能量平衡（Williams 和 Maresh，2016）。其他物种，包括海豹和须鲸，能量消耗率较低，使它们能够在高能量获取率和禁食之间交替。这些动物在更大的空间（数百至数千公里）和时间（数月至数年）尺度上实现能量平衡。这一策略利用季节性生产环境，建立能源储备，以便在没有食物时使用。尽管极地地区的维护成本可能会升高，但极地夏季与海冰相关的季节性高生产力支持高能量获取率，这足以弥补这一不足。随着时间的推移，鲸鱼在极地冬季面临着高昂的繁殖成本，它们选择了热量更温和但能源匮乏的热带地区。在热带地区度过的时光也提供了修复和“翻新”皮肤的机会（Durban 和 Pitman，2012）。作为专性食草动物，海牛和儒艮已经适应了以海草和其他水生植物为食，这些植物含量丰富但热量较低。海妖能够通过生活在热带环境中来抵消低能量摄入率，这使得维护成本较低，同时食用几乎不需要能量即可获得的草食性饮食。然而，现存海牛的热量限制让人好奇北海牛是如何靠海带在白令海寒冷的海水中生存的（Estes et al., 2016）。虽然最好的情况是获得丰富的、高能量的猎物，但在某些情况下，更丰富且更接近的低质量猎物可能比寻找难以找到的高质量猎物更理想。随着猎物变得越来越少，寻找猎物的成本就会增加，动物会花费更多的时间和精力来寻找猎物。最终，存在一个阈值，超过该阈值，用于寻找猎物的能量多于获得的能量，动物就会进入负能量平衡（Villegas-Amtmann 等，2015）。
Measurement of energy acquisition and allocation provides a quantitative assessment of how animals organize their daily or seasonal activities, and how they prioritize their behaviors to maximize fitness. What goes in as food and comes out as growth, reproduction, repair, waste, or metabolic work can be described by energy flow models (Fig. 1). At a minimum, survival requires that the individual breaks even in terms of energy costs and benefits, balancing the costs of self-maintenance versus energy acquired. To grow and reproduce, animals must obtain more energy than is needed to survive, so that they are in positive energy balance. Many marine mammals undergo variations in energy balance, gaining energy while feeding in highly productive environments, followed by fasting during migration or reproduction. This balance between energy acquisition and expenditure, as well as the temporal and spatial scales across which it is achieved, differs markedly between species and environments. For some species, including sea otters, sea lions, and fur seals, high rates of energy expenditure are met by high rates of energy acquisition (Costa and Williams, 2000). These animals preferentially live in nearshore environments or upwelling regions where food is abundant (Costa, 1993), finding energy balance on smaller (10s to 100s of kilometers), more immediate (daily to weekly) scales (Williams and Maresh, 2016). Other species, including seals and baleen whales, have low rates of energy expenditure, allowing them to alternate between high rates of energy acquisition and fasting. These animals achieve energy balance over larger spatial (100s to 1000s of kilometers) and time (months to years) scales. This strategy takes advantage of seasonally productive environments, building energy reserves that can be used when food is not available. Although maintenance costs may be elevated in polar regions, the seasonally high productivity associated with sea ice during the polar summer supports high-energy acquisition rates that more than compensate. As time passes and whales are confronted with the high costs of reproduction during a polar winter, they opt for the more thermally benign but energy-poor tropics. Spending time in the tropics also provides an opportunity to repair and “refurbish” their skin (Durban and Pitman, 2012). As obligate herbivores, manatees and dugongs have adapted to a diet of seagrasses and other aquatic plants that are in high abundance but of low caloric value. Sirenians are able to offset low energy intake rates by living in tropical environment that keeps maintenance costs low while consuming a herbivorous diet that takes little energy to acquire. However, the thermal constraints of extant sirenians make one wonder how the Steller sea cow managed to survive in the cold waters of the Bering Sea on a diet of kelp (Estes et al., 2016). While the best situation is to have access to abundant, high-energy prey, in some scenarios low-quality prey that is more abundant and nearby may be more optimal than searching for high-quality prey that is difficult to find. As prey becomes less available, the cost of finding it increases and the animal spends a greater proportion of its time and therefore energy searching for it. Eventually, there is a threshold beyond which more energy is spent searching for prey than is obtained and the animal goes into negative energy balance (Villegas-Amtmann et al., 2015).