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Marginal value theorem
The marginal value theorem (MVT) is an optimality model that usually describes the behavior of an optimally foraging individual in a patchy system, but it can also be applied to other situations in which organisms face diminishing returns. The resources (often food) in patchy systems are located in discrete patches separated by areas with no resources. Due to the resource-free space, animals must spend time traveling between patches.
==Defining the MVT==
All animals must forage for food in order to meet their energetic needs, but doing so is energetically costly. It is assumed that evolution by natural selection results in animals utilizing the most economic and efficient strategy to balance energy gain and consumption. The Marginal Value Theorem is an optimality model that describes the strategy that maximizes gain per unit time in systems where resources, and thus rate of returns, decrease with time.〔(G.A. “Marginal Value Theorem with Exploitation Time Costs: Diet, Sperm Reserves, and Optimal Copula Duration in Dung Flies” (1992) The American Naturalist 139(6):1237-1256 )〕 The model weighs benefits and costs and is used to predict giving up time and giving up density. Giving up time (GUT) is the interval of time between when the animal last feeds and when it leaves the patch. Giving up density (GUD) is the food density within a patch when the animal will choose to move on to other food patches.
When an animal is foraging in a system where food sources are patchily distributed, the MVT can be used to predict how much time an individual will spend searching for a particular patch before moving on to a new one. In general, individuals will stay longer if (1) patches are farther apart and thus there is a higher cost of travel or (2) current patches are rich in resources.
A more recent study conducted by Ben Marwick in Northwest Thailand, presented an alternative way of looking at the Marginal Value Theorem. Rather than the traditional single optimal point, Marwick redrew the schematic in order to present the possibility of there being two optimum states. He calls this multiple optima.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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