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

K12 Standards

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Life Science

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Heredity: Inheritance and Variation of Traits

HS-LS4-2

Optimal Foraging

Muitas vezes, na vida, as coisas de que um indivíduo precisa podem não estar ao alcance imediato. Então, os organismos precisam forragear. O forrageamento é definido simplesmente como o processo de busca de alimentos ou, mais geralmente, recursos. Embora a comida seja provavelmente o primeiro exemplo que vem à mente, os organismos devem procurar outros recursos, como abrigo ou companheiros, e os animais geralmente fazem de tudo para obter o que precisam. No entanto, o próprio ato de forrageamento requer energia. Essencialmente, os indivíduos devem equilibrar a queima de calorias com a obtenção delas. Simplificando, o forrageamento requer uma estratégia. Os ecologistas criaram a teoria do forrageamento ideal para modelar as circunstâncias em que um organismo atinge o equilíbrio ideal entre a energia gasta no forrageamento, ou seja, o valor de duas bolotas e a energia potencial que ele pode adquirir como seis novas bolotas. 
Uma característica do forrageamento é que os recursos nem sempre são distribuídos uniformemente dentro de um habitat. Mais tipicamente, os recursos estão contidos em patches entre os quais os forrageadores devem se mover. Então, como exatamente os forrageadores devem navegar por esses trechos de recursos? Em 1976, o ecologista evolucionista Eric L. Charnov criou o teorema do valor marginal ou MVT para explicar como os organismos otimizam seu forrageamento. O MVT tem cinco previsões principais para o forrageamento ideal. Primeiro, afirma que as forrageadoras devem capturar mais presas em manchas com alta densidade de presas do que em manchas de baixa densidade de presas. Em segundo lugar, a teoria prevê que as forrageadoras devem gastar mais tempo caçando recursos em manchas de alta densidade de presas. Em seguida, a forrageira deve ter uma taxa de captura de presas mais alta em ambientes densos com manchas compactadas do que em ambientes esparsos com manchas espalhadas mais distantes. A quarta previsão afirma que as forrageadoras passarão mais tempo forrageando nesses ambientes densos do que em ambientes esparsos. Finalmente, um forrageador deve deixar um patch quando a taxa de captura tiver diminuído para a taxa média de todos os patches. E é aqui que entra um conceito chamado desistir do tempo ou GUT. Para calcular o GUT, basta subtrair o tempo em que a presa final foi adquirida do momento em que o indivíduo deixa o canteiro. Portanto, o GUT deve ser o mesmo para todos os patches que um forrageador visita. 
Neste laboratório, você completará simulações de forrageamento em vários patches de recursos artificiais diferentes e, em seguida, realizará cálculos para avaliar o desempenho de sua classe como forrageadores e se você aderiu às regras do teorema do valor marginal.

forrageamento ideal

<h4>Forrageamento ideal</h4>
Os organismos devem adquirir e usar recursos em seu ambiente para sobreviver. Embora a comida seja um dos principais recursos que os organismos devem procurar, os indivíduos também precisam procurar habitats, abrigo e parceiros. Esse processo de busca de recursos é conhecido como forrageamento, que envolve uma série de custos e benefícios. Mais especificamente, a aquisição de um recurso fornece um benefício ao organismo, no entanto, procurar e capturar o recurso requer gasto de tempo e energia. Assim, os organismos adotam estratégias de forrageamento que maximizam o ganho líquido a um nível ideal, proporcionando o maior benefício pelo menor custo. Os ecologistas desenvolveram a "Teoria do Forrageamento Ideal" para modelar as situações em que um organismo atinge o equilíbrio ideal entre custos e benefícios de forrageamento.
<h4>O Teorema do Valor Marginal</h4>
Os recursos não são distribuídos uniformemente no ambiente. Por exemplo, em um ecossistema florestal, é muito mais provável encontrar espécies de árvores agrupadas em vez de distribuídas uniformemente por toda a floresta. Essa heterogeneidade na disponibilidade de recursos cria "patches" de recursos. Portanto, os forrageadores devem considerar tanto a recompensa de um patch quanto a distância entre os patches, portanto, o custo de mudar para outro patch. O Teorema do Valor Marginal (MVT) descreve como as forrageadoras ideais utilizam e se movem entre manchas de recursos em seu habitat 1. Existem cinco previsões principais do MVT: 
<ol class="referências">
	<li>As forrageadoras devem capturar mais presas em manchas de alta densidade de presas do que em áreas de baixa densidade de presas.</li>
	<li>As forrageadoras devem passar mais tempo forrageando em manchas de alta densidade de presas do que naquelas com baixa densidade de presas.</li>
	<li>As forrageadoras devem ter uma taxa de captura de presas mais alta em manchas densas do que aquelas que estão mais distantes.</li>
	<li>As forrageadoras devem passar mais tempo forrageando em ambientes densos, onde os patches são agrupados, do que em ambientes esparsos.</li>
	<li>Os forrageadores devem deixar um patch quando a taxa de captura diminuir para a taxa média de todos os patches.</li>
</ol>
O intervalo de tempo entre o momento em que a última presa é capturada e o momento em que a forrageadora deixa o canteiro é conhecido como Giving-Up-Time, ou GUT. No contexto do MVT, o GUT deve ser o mesmo em todos os patches para cada forrageador individual. Isso foi testado em um experimento com chapins-de-cabeça-preta em um grande aviário em busca de larvas de farinha escondidas em pinhas artificiais, onde as aves tinham o mesmo GUT para todos os tipos de manchas, o que estava inversamente relacionado à taxa média de captura para todo o ambiente 2. 
Quanto mais tempo um organismo passa forrageando, mais energia ele gasta e mais tempo se expõe a predadores e elementos, portanto, desenvolver uma estratégia de forrageamento ideal para aquisição de recursos é essencial para a maioria dos organismos. Os princípios do MVT têm muitas aplicações na vida real para promover a diversidade, a conservação e até mesmo o comportamento humano.
<h4>Forrageamento ideal em um ambiente em mudança</h4>
Do ponto de vista da diversidade e conservação, o MVT preveria que as espécies só podem existir se houver manchas para atender adequadamente às necessidades energéticas de um organismo, portanto, a disponibilidade e a distância entre os recursos são importantes para os organismos que dependem deles para sobreviver. A perda de habitat, poluição e outras mudanças no ambiente podem interferir na capacidade de um organismo de forragear de maneira ideal, reduzindo assim sua aptidão. Assim, quando os habitats de um ecossistema são destruídos, manchas ou comunidades inteiras são removidas. Essa remoção limita os recursos disponíveis para os habitantes do resto de um ecossistema. Menos manchas com recursos criam uma competição mais intensa e podem eliminar certas espécies. Isso é particularmente importante para espécies ameaçadas de extinção devido à perda de habitat, que não conseguirão atender às suas necessidades de forrageamento se a maior parte de seu habitat for destruída. 
Os humanos desenvolveram um armazenamento sofisticado de alimentos para limitar as necessidades de forrageamento, no entanto, existem muitos outros casos em que o forrageamento é necessário, como procurar moradia acessível, um emprego bem remunerado ou encontrar uma data adequada, entre outros. Um estudo recente testou as previsões do MVT usando as habilidades de busca de informações dos clínicos gerais. Eles descobriram que os clínicos gerais procuravam informações ao diagnosticar um paciente; Eles se moveram rapidamente entre várias fontes de informação e utilizaram fontes de alta densidade, como a Internet, e fontes facilmente alcançáveis, incluindo seus colegas com frequência 3. Da mesma forma, a Teoria do Forrageamento Ideal também se aplica à economia na forma como os consumidores compram ou "forrageiam" produtos e informações ao fazer uma compra 4. Esses estudos demonstram como os humanos aderem às previsões da teoria de forrageamento ideal em uma variedade de contextos.
<h4>Referências</h4>
<ol>
	<li>Charnov, E. L. forrageamento ptimal: o teorema do valor marginal. Biologia Populacional Teórica. 1976, Vol. 9, (129-36).</li>
	<li>John Krebs, John Ryan, Eric Charnov. Caça por expectativa ou forrageamento ideal: um estudo do uso de manchas por chapins. comportamento animal. 1974, Vol. 22, (953-64).</li>
	<li>Mai Dwairy, Anthony C Dowell, Jean-Claude Stahl. A aplicação da teoria do forrageamento ao comportamento de busca de informações de clínicos gerais. Prática de Família BMC. 2011, Vol. 12, 90.</li>
	<li>Poços, V.K. Forrageamento: um modelo ecológico de comportamento do consumidor? Teoria do Marketing. 2012, Vol. 2, 12 (117-136).</li>
</ol>

Forrageamento ideal

Forrageamento ideal
Os organismos devem adquirir e usar recursos em seu ambiente para sobreviver. Embora a comida seja um dos principais recursos que os organismos devem ...

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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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Patch Use in Optimal Foraging

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