Name: patch use in optimal foraging
Uploaded: 2019-01-29T11:04:46.000Z
Duration: 3 min 37 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS4-2

Optimal Foraging

在生命中，个体所需的事物往往无法立即获得，因此生物需要觅食。觅食简单来说就是寻找食物或更广义资源的过程。尽管食物可能是最先想到的例子，但生物还必须寻找其他资源，例如庇护所或配偶，动物常常会付出巨大努力来获取所需。然而，觅食行为本身需要消耗能量。本质上，个体必须在消耗卡路里与获取卡路里之间取得平衡。简而言之，觅食需要策略。生态学家提出了最优觅食理论，用以模拟生物在觅食过程中所消耗的能量（例如相当于两个橡子的能量）与其可能获得的能量（例如六个新橡子）之间达到最佳平衡的情形。
觅食的一个特征是，资源在栖息地内并不总是均匀分布的。更常见的情况是，资源集中在若干斑块中，觅食者必须在这些斑块之间移动。那么，觅食者究竟应如何在这些资源斑块间进行导航？1976年，进化生态学家Eric L. Charnov提出了边际值理论（marginal value theorem, MVT），用以解释生物体如何优化其觅食行为。MVT对最优觅食提出了五个主要预测。第一，该理论指出，在猎物密度高的斑块中，觅食者应比在猎物密度低的斑块中捕获更多的猎物。第二，理论预测觅食者应在猎物密度高的斑块中花费更多时间搜寻资源。第三，当高密度环境中的斑块彼此靠近时，觅食者的猎物捕获率应高于斑块分布稀疏的低密度环境。第四项预测指出，觅食者在密集环境中的觅食时间应长于在稀疏环境中的觅食时间。最后，当某一斑块内的捕获率下降至所有斑块的平均捕获率时，觅食者应当离开该斑块。这便引入了一个称为“放弃时间”（giving up time, GUT）的概念。计算GUT的方法是：用个体离开斑块的时间减去最后一次获取猎物的时间。因此，对于同一觅食者访问的所有斑块，其GUT应当保持一致。
在本实验中，您将在多个不同的人工资源斑块中完成觅食模拟，然后进行计算，以评估您所在班级作为觅食者的表现，并判断是否遵循了边际价值定理的原则。

最优觅食

<h4>最适觅食</h4>
生物体必须获取并利用环境中的资源以维持生存。虽然食物是生物体需要寻找的主要资源之一，但个体还需要寻找栖息地、庇护所和配偶。这种寻找资源的过程被称为觅食，其中涉及一系列成本与收益的权衡。具体而言，获取资源能为生物体带来收益，但搜寻和捕获资源需要耗费时间和能量。因此，生物体会采用觅食策略，以在最低成本下获得最大收益，从而使净收益达到最优水平。生态学家提出了“最优觅食理论”，用于模拟生物体在觅食成本与收益之间达到最佳平衡的条件。
<h4>边际价值定理</h4>
资源在环境中并非均匀分布。例如，在森林生态系统中，树种更倾向于成簇分布，而不是在整个森林中均匀分布。这种资源可用性的异质性形成了资源“斑块”。因此，觅食者必须同时考虑一个斑块的收益以及斑块之间的距离，即转移到另一个斑块所需付出的移动代价。边际值定理（Marginal Value Theorem, MVT）描述了最优觅食者如何在其栖息地中利用资源斑块并在这之间移动1。MVT 包含五个主要预测：
<ol class="references">
	<li>捕食者在猎物密度高的区域所捕获的猎物数量应多于猎物密度低的区域。</li>
	<li>捕食者在猎物密度高的区域中觅食的时间应长于在猎物密度低的区域。</li>
	<li>与分布较稀疏的区域相比，捕食者在密集区域中的猎物捕获率应更高。</li>
	<li>捕食者在密集环境中（即区域呈簇状聚集）的觅食时间应长于在稀疏环境中。</li>
	<li>当捕获率下降至所有区域平均捕获率时，捕食者应离开该区域。</li>
</ol>
当捕食者捕获最后一只猎物到离开斑块之间的时间间隔被称为放弃时间（Giving-Up-Time，简称 GUT）。在边际值理论（MVT）的框架下，每个个体觅食者的 GUT 在所有斑块中应保持一致。这一预测在一项针对黑顶山雀的实验中得到了验证：实验中，鸟类在大型 aviary 内从人工松果中搜寻隐藏的黄粉虫，结果发现，鸟类在各类斑块中的 GUT 相同，且该时间与整个环境中的平均捕获率呈反比关系2。
生物体觅食的时间越长，消耗的能量就越多，暴露于捕食者和外界环境中的时间也越长，因此，为获取资源而制定最优觅食策略对大多数生物体而言至关重要。边际价值理论（MVT）的原理在促进生物多样性、保护生态以及研究人类行为等方面具有诸多实际应用。
<h4>变化环境中的最优觅食</h4>
从多样性和保护的角度来看，最小可存活种群理论（MVT）预测，只有当存在足够满足生物体能量需求的资源斑块时，物种才能生存，因此资源的可获得性及其之间的距离对于依赖这些资源生存的生物体至关重要。栖息地丧失、污染以及环境中的其他变化可能干扰生物体最优觅食的能力，从而降低其适合度。因此，当生态系统中的栖息地遭到破坏时，资源斑块或整个生物群落可能被移除。这种移除限制了生态系统其余部分居民可利用的资源。资源斑块减少会导致更激烈的竞争，并可能导致某些物种消失。这对于因栖息地丧失而面临灭绝威胁的物种尤为重要，因为一旦其大部分栖息地被破坏，它们将无法满足自身的觅食需求。
人类已经发展出复杂的食品储存方式以减少觅食需求，但在许多其他情况下，觅食仍然是必要的，例如寻找负担得起的住房、收入较高的工作，或在众多选择中找到合适的约会对象等。最近一项研究利用全科医生获取信息的能力来检验最优觅食理论（MVT）的预测。研究发现，全科医生在诊断患者时会以最优策略进行信息觅食；他们快速在多个信息来源之间切换，并频繁利用高信息密度的来源（如互联网）以及容易获取的信息来源（如同事）3。同样，最优觅食理论也适用于经济学领域中消费者购物行为，即消费者在购买决策过程中如何“觅食”产品和相关信息4。这些研究表明，人类在多种情境下均遵循最优觅食理论的预测。
<h4>参考文献</h4>
<ol>
	<li>Charnov, E. L. 最优觅食：边际值定理。Theoretical Population Biology. 1976, Vol. 9, (129-36)。</li>
	<li>John Krebs, John Ryan, Eric Charnov. 基于预期的捕食还是最优觅食：一项关于山雀利用斑块行为的研究。Animal Behaviour. 1974, Vol. 22, (953-64)。</li>
	<li>Mai Dwairy, Anthony C Dowell, Jean-Claude Stahl. 觅食理论在全科医生信息搜索行为中的应用。BMC Family Practice. 2011, Vol. 12, 90。</li>
	<li>Wells, V.K. 觅食：一种消费者行为的生态学模型？Marketing Theory. 2012, Vol. 2, 12 (117-136)。</li>
</ol>

最优觅食
生物体必须获取并利用环境中的资源以维持生存。食物是生物体必须获取的主要资源之一……

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最佳觅食

patch use in optimal foraging

Patch use in optimal foraging explains how organisms balance food gain against the time and energy needed to search for it. Foraging is not limited to food. Animals also search for habitats, shelter, and mates. Each choice has costs and benefits. A resource provides a benefit, but finding and capturing it takes effort. Optimal Foraging Theory models how organisms reach the best balance between those costs and gains.

A key idea in this theory is that resources are often clumped into patches rather than spread evenly through an environment. Forest trees, for example, are more likely to occur in groups than as single, evenly spaced trees. Because of this patchiness, foragers must think about both the value of a patch and the distance to the next one. Moving between patches also has a cost. The Marginal Value Theorem helps explain when an organism should keep feeding in a patch and when it should move on.

The Marginal Value Theorem predicts that foragers should capture more prey in dense patches than in sparse ones. They should also spend more time in patches with more prey, and they should have a higher prey capture rate there. In dense environments, where patches are closer together, foragers should spend more time foraging than in sparse environments. A forager should leave a patch when the capture rate falls to the average rate for the whole environment. The time between the last prey capture and leaving the patch is called the Giving-Up-Time, or GUT.

The GUT should be the same across patches for a single forager. This prediction was tested with black-capped chickadees in a large aviary. The birds searched for mealworms hidden in artificial pine cones. They showed the same GUT in all patch types, and that GUT was inversely related to the average capture rate in the environment. The result supported the Marginal Value Theorem.

Optimal foraging matters because searching takes time, uses energy, and can expose organisms to predators and the elements. It also helps explain real-world ecology and conservation. Habitat loss, pollution, and other environmental changes can disrupt foraging and lower fitness. If habitats are destroyed, patches and even whole communities may disappear. That reduces the resources available to the rest of the ecosystem and can increase competition. Species at risk of extinction may be especially affected if most of their habitat is lost.

The same ideas also apply to human behavior. Humans reduce foraging needs through food storage, but they still forage in other ways. People may search for affordable housing, a well-paying job, or a suitable date. A study of general practitioners found that they foraged for information while diagnosing patients. They moved quickly between sources and used both high-density sources, such as the internet, and easier sources, including colleagues. Optimal Foraging Theory also helps explain how consumers search for products and information when making purchases.

Patch Use in Optimal Foraging

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Patch use in optimal foraging explains how organisms balance food gain against the time and energy needed to search for it. Foraging is not limited to food. Animals also search for habitats, shelter, and mates. Each choice has costs and benefits. A resource provides a benefit, but finding and capturing it takes effort. Optimal Foraging Theory models how organisms reach the best balance between those costs and gains. A key idea in this theory is that resources are often clumped into patches...

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Learn how optimal foraging theory explains patch use, Giving-Up-Time, and the Marginal Value Theorem using chickadees, conservation, and human examples.

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Cancer Prevention

Several factors can increase the risk of cancer in an individual. About 50% of cancer cases can be prevented by adopting a healthy lifestyle, regular ...

cancers-originate-from-somatic-mutations-in-a-single-cell

Cancers Originate from Somatic Mutations in a Single Cell

Cancer arises from mutations in the critical genes that allow healthy cells to escape cell cycle regulation and acquire the ability to proliferate ...

DNA Distortion and Damage
Cells are regularly exposed to mutagens&#8212;factors in the environment that can damage DNA and generate mutations. UV ...

comparing-copy-number-variations-and-snps

Comparing Copy Number Variations and SNPs

Sequencing of the human genome has opened up several best-kept secrets of the genome. Scientists have identified thousands of genome variations that exist ...

Gene Conversion

Other than maintaining genome stability via DNA repair, homologous recombination plays an important role in diversifying the genome. In fact, the ...

Mutations

Overview

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. ...

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions ...

Make and defend a claim based on evidence that inheritable genetic variations may result from (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and or (3) mutations caused by environmental factors. [Clarification Statement: Emphasis is on using data to support arguments for the way variation occurs.] [Assessment Boundary: Assessment does not include the phases of meiosis or the biochemical mechanism of specific steps in the process.]

HS-LS3-2

Patch Use in Optimal Foraging

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