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

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Life Science

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Heredity: Inheritance and Variation of Traits

HS-LS4-2

Optimal Foraging

Souvent dans la vie, les choses dont un individu a besoin ne sont pas à portée de main. Les organismes ont donc besoin de se nourrir. La recherche de nourriture est définie simplement comme le processus de recherche de nourriture ou plus généralement de ressources. Bien que la nourriture soit probablement le premier exemple qui vient à l’esprit, les organismes doivent chercher d’autres ressources comme un abri ou des partenaires et les animaux se donnent souvent beaucoup de mal pour obtenir ce dont ils ont besoin. Cependant, l’acte de chercher de la nourriture lui-même nécessite de l’énergie. Essentiellement, les individus doivent trouver un équilibre entre brûler des calories et les obtenir. Pour faire simple, la recherche de nourriture nécessite une stratégie. Les écologistes ont créé la théorie de la recherche de nourriture optimale pour modéliser les circonstances dans lesquelles un organisme atteint l'équilibre optimal entre l'énergie dépensée pour la recherche de nourriture, c'est-à-dire la valeur de deux glands et l'énergie potentielle qu'il peut acquérir comme six nouveaux glands. 
L’une des caractéristiques de la recherche de nourriture est que les ressources ne sont pas toujours réparties uniformément dans un habitat. Plus généralement, les ressources sont contenues dans des parcelles entre lesquelles les butineurs doivent se déplacer. Alors, comment les butineurs devraient-ils naviguer dans ces parcelles de ressources ? En 1976, l’écologiste évolutionniste Eric L. Charnov a proposé le théorème de la valeur marginale ou MVT pour expliquer comment les organismes optimisent leur recherche de nourriture. Le MVT a cinq prédictions principales pour une recherche de nourriture optimale. Premièrement, il stipule que les butineuses devraient capturer plus de proies dans les parcelles à forte densité de proies que dans les parcelles à faible densité de proies. Deuxièmement, la théorie prédit que les butineurs devraient passer plus de temps à chasser les ressources dans les zones à forte densité de proies. Ensuite, le butineur devrait avoir un taux de capture de proies plus élevé dans les environnements denses avec des parcelles serrées les unes contre les autres que dans les environnements clairsemés avec des parcelles plus éloignées. La quatrième prédiction indique que les butineuses passeront plus de temps à chercher de la nourriture dans ces environnements denses que dans des environnements clairsemés. Enfin, un butineur doit quitter une parcelle lorsque le taux de capture a diminué pour atteindre le taux moyen de toutes les parcelles. Et c’est là qu’intervient un concept appelé renoncer au temps ou GUT. Pour calculer le GUT, il suffit de soustraire le temps pendant lequel la proie finale a été acquise du moment où l’individu quitte la parcelle. Par conséquent, le GUT doit être le même pour toutes les parcelles qu’un butineur visite. 
Dans ce laboratoire, vous effectuerez des simulations de recherche de nourriture dans plusieurs parcelles de ressources artificielles différentes, puis effectuerez des calculs pour évaluer comment votre classe s’est comportée en tant que butineuses et si vous avez respecté les règles du théorème de valeur marginale.

alimentation optimale

<h4>Alimentation optimale</h4>
Les organismes doivent acquérir et utiliser les ressources de leur environnement pour survivre. Bien que la nourriture soit l’une des principales ressources que les organismes doivent rechercher, les individus doivent également rechercher des habitats, des abris et des partenaires. Ce processus de recherche de ressources est connu sous le nom de recherche de nourriture, qui implique une série de coûts et d’avantages. Plus précisément, l’acquisition d’une ressource procure un avantage à l’organisme, mais la recherche et la capture de la ressource nécessitent une dépense de temps et d’énergie. Ainsi, les organismes adoptent des stratégies de recherche de nourriture qui maximisent le gain net à un niveau optimal en offrant le plus d’avantages au coût le plus bas. Les écologistes ont développé la « théorie de la recherche de nourriture optimale » pour modéliser les situations dans lesquelles un organisme atteint l’équilibre optimal entre les coûts et les avantages de la recherche de nourriture.
<h4>Le théorème de la valeur marginale</h4>
Les ressources ne sont pas uniformément réparties dans l’environnement. Par exemple, dans un écosystème forestier, il est beaucoup plus probable de trouver des espèces d’arbres regroupées plutôt que réparties uniformément dans toute la forêt. Cette hétérogénéité de la disponibilité des ressources crée des « patchs » de ressources. Par conséquent, les butineurs doivent tenir compte à la fois du rendement d’une parcelle et de la distance entre les parcelles, donc du coût du déplacement vers une autre parcelle. Le théorème de la valeur marginale (MVT) décrit comment les butineurs optimaux utilisent et se déplacent entre les parcelles de ressources de leur habitat 1. Il y a cinq prédictions principales du MVT : 
<ol class="références">
	<li>Les butineuses devraient capturer plus de proies dans les parcelles à forte densité de proies que dans les parcelles à faible densité de proies.</li>
	<li>Les butineuses devraient passer plus de temps à chercher de la nourriture dans les parcelles à forte densité de proies que dans celles à faible densité de proies.</li>
	<li>Les butineuses devraient avoir un taux de capture de proies plus élevé dans les parcelles denses que celles qui sont dispersées plus loin.</li>
	<li>Les butineuses devraient passer plus de temps à chercher de la nourriture dans des environnements denses, où les parcelles sont regroupées, que dans des environnements clairsemés.</li>
	<li>Les butineuses doivent quitter une parcelle lorsque le taux de capture a diminué pour atteindre le taux moyen de toutes les parcelles.</li>
</ol>
L’intervalle de temps entre le moment où la dernière proie est capturée et le moment où le butineur quitte la parcelle est connu sous le nom de temps d’abandon, ou GUT. Dans le contexte du MVT, la GUT doit être la même dans toutes les parcelles pour chaque butineuse. Cela a été testé dans une expérience avec des mésanges à tête noire dans une grande volière à la recherche de vers de farine cachés dans des pommes de pin artificielles, où les oiseaux avaient le même GUT pour tous les types de taches, ce qui était inversement proportionnel au taux de capture moyen pour l’ensemble de l’environnement 2. 
Plus un organisme passe de temps à chercher de la nourriture, plus il dépense d’énergie et plus il s’expose aux prédateurs et aux éléments, donc le développement d’une stratégie de recherche de nourriture optimale pour l’acquisition de ressources est essentiel pour la plupart des organismes. Les principes du MVT ont de nombreuses applications réelles pour promouvoir la diversité, la conservation et même le comportement humain.
<h4>Alimentation optimale dans un environnement changeant</h4>
Du point de vue de la diversité et de la conservation, le MVT prédirait que les espèces ne peuvent exister que s’il existe des parcelles pour répondre adéquatement aux besoins énergétiques d’un organisme, donc la disponibilité et la distance entre les ressources sont importantes pour les organismes qui en dépendent pour leur survie. La perte d’habitat, la pollution et d’autres changements dans l’environnement peuvent interférer avec la capacité d’un organisme à se nourrir de manière optimale, réduisant ainsi sa valeur adaptative. Ainsi, lorsque les habitats d’un écosystème sont détruits, des parcelles ou des communautés entières sont éliminées. Cette suppression limite les ressources disponibles pour les habitants du reste d’un écosystème. Moins de parcelles avec des ressources crée une concurrence plus intense et peut éliminer certaines espèces. Ceci est particulièrement important pour les espèces menacées d’extinction en raison de la perte d’habitat qui ne seront pas en mesure de répondre à leurs besoins en matière de nourriture si la majeure partie de leur habitat est détruite. 
Les humains ont développé un stockage sophistiqué de la nourriture pour limiter les besoins en matière de recherche de nourriture, mais il existe de nombreux autres cas dans lesquels la recherche de nourriture est nécessaire, comme la recherche d’un logement abordable, d’un emploi bien rémunéré ou de la recherche d’une date appropriée, entre autres. Une étude récente a testé les prédictions du MVT en utilisant les capacités de recherche d’informations des médecins généralistes. Ils ont constaté que les médecins généralistes cherchaient de manière optimale des informations lors du diagnostic d’un patient ; Ils se sont rapidement déplacés entre plusieurs sources d’information et ont utilisé à la fois des sources à haute densité, telles qu’Internet, et des sources facilement accessibles, y compris leurs collègues fréquemment 3. De même, la théorie de la recherche de nourriture optimale s’applique également à l’économie dans la façon dont les consommateurs achètent ou « cherchent » des produits et des informations lors d’un achat 4. Ces études démontrent comment les humains adhèrent aux prédictions de la théorie de la recherche de nourriture optimale dans une variété de contextes.
<h4>Références</h4>
<ol>
	<li>Charnov, E. L. Quête de nourriture ptimale : le théorème de la valeur marginale. Biologie théorique des populations. 1976, vol. 9, (129-36).</li>
	<li>John Krebs, John Ryan, Eric Charnov. Chasse par attente ou recherche de nourriture optimale : une étude sur l’utilisation des parcelles par les mésanges. comportement animal. 1974, vol. 22, (953-64).</li>
	<li>Mai Dwairy, Anthony C Dowell, Jean-Claude Stahl. L’application de la théorie de la recherche de nourriture au comportement de recherche d’information des médecins généralistes. Médecine familiale BMC. 2011, vol. 12, 90.</li>
	<li>Wells, V.K. La cueillette : un modèle écologique du comportement des consommateurs ? Théorie du marketing. 2012, vol. 2, 12 (117-136).</li>
</ol>

Alimentation optimale

Alimentation optimale
Les organismes doivent acquérir et utiliser les ressources de leur environnement pour survivre. Bien que la nourriture soit l’une des principales ressources, les organismes doivent ...

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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.

Patch Use in Optimal Foraging | JoVE K12

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Patch Use in Optimal Foraging

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