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. 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.
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