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

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Heredity: Inheritance and Variation of Traits

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Optimal Foraging

Spesso nella vita, le cose di cui un individuo ha bisogno possono non essere a portata di mano. Quindi, gli organismi hanno bisogno di foraggiare. Il foraggiamento è definito semplicemente come il processo di ricerca di cibo o più in generale di risorse. Anche se il cibo è probabilmente il primo esempio che viene in mente, gli organismi devono cercare altre risorse come un riparo o compagni e gli animali spesso fanno di tutto per ottenere ciò di cui hanno bisogno. Tuttavia, l'atto stesso di foraggiare richiede energia. In sostanza, gli individui devono bilanciare il consumo di calorie con l'ottenimento. Per dirla semplicemente, il foraggiamento richiede una strategia. Gli ecologi hanno creato la teoria del foraggiamento ottimale per modellare le circostanze in cui un organismo raggiunge l'equilibrio ottimale tra l'energia spesa per il foraggiamento, cioè il valore di due ghiande e l'energia potenziale che può acquisire come sei nuove ghiande. 
Una caratteristica del foraggiamento è che le risorse non sono sempre distribuite uniformemente all'interno di un habitat. Più tipicamente, le risorse sono contenute in appezzamenti tra i quali i raccoglitori devono spostarsi. Quindi, in che modo esattamente i raccoglitori dovrebbero navigare in queste zone di risorse? Nel 1976, l'ecologo evoluzionista Eric L. Charnov ideò il teorema del valore marginale o MVT per spiegare come gli organismi ottimizzano il loro foraggiamento. L'MVT ha cinque previsioni principali per un foraggiamento ottimale. In primo luogo, afferma che i raccoglitori dovrebbero catturare più prede in aree con un'alta densità di prede rispetto a quelle a bassa densità di prede. In secondo luogo, la teoria prevede che i raccoglitori dovrebbero trascorrere più tempo a caccia di risorse in aree ad alta densità di prede. Successivamente, il raccoglitore dovrebbe avere un tasso di cattura delle prede più elevato in ambienti densi con chiazze ravvicinate rispetto ad ambienti sparsi con chiazze più distanti. La quarta previsione afferma che i raccoglitori trascorreranno più tempo a cercare cibo in questi ambienti densi che in ambienti radi. Infine, un raccoglitore dovrebbe lasciare una patch quando il tasso di cattura è sceso al tasso medio di tutte le patch. Ed è qui che entra in gioco un concetto chiamato rinunciare al tempo o GUT. Per calcolare il GUT, è sufficiente sottrarre il tempo in cui l'oggetto della preda finale è stato acquisito dal momento in cui l'individuo lascia la chiazza. Pertanto, l'intestino dovrebbe essere lo stesso per tutte le macchie visitate da un raccoglitore. 
In questo laboratorio, completerai simulazioni di foraggiamento in diverse patch di risorse artificiali e quindi eseguirai calcoli per valutare come la tua classe si è comportata come raccoglitori e se hai aderito alle regole del teorema del valore marginale.

foraggiamento ottimale

<h4>Foraggiamento ottimale</h4>
Gli organismi devono acquisire e utilizzare le risorse del loro ambiente per sopravvivere. Mentre il cibo è una delle risorse primarie che gli organismi devono cercare, gli individui devono anche cercare habitat, ripari e compagni. Questo processo di ricerca delle risorse è noto come foraggiamento, che comporta una serie di costi e benefici. Più specificamente, l'acquisizione di una risorsa fornisce all'organismo un beneficio, tuttavia, la ricerca e l'acquisizione della risorsa richiede un dispendio di tempo ed energia. Pertanto, gli organismi adottano strategie di foraggiamento che massimizzano il guadagno netto a un livello ottimale fornendo il massimo beneficio al minor costo. Gli ecologi hanno sviluppato la "Teoria del Foraggiamento Ottimale" per modellare le situazioni in cui un organismo raggiunge l'equilibrio ottimale tra costi e benefici del foraggiamento.
<h4>Il teorema del valore marginale</h4>
Le risorse non sono distribuite uniformemente nell'ambiente. Ad esempio, in un ecosistema forestale, è molto più probabile trovare specie di alberi raggruppate insieme piuttosto che distribuite uniformemente in tutta la foresta. Questa eterogeneità nella disponibilità delle risorse crea "patch" di risorse. Pertanto, i raccoglitori devono considerare sia il guadagno di un appezzamento che la distanza tra i cerotti, quindi il costo del passaggio a un altro appezzamento. Il teorema del valore marginale (MVT) descrive il modo ottimale in cui i raccoglitori utilizzano e si spostano tra le aree di risorse nel loro habitat 1. Ci sono cinque previsioni principali dell'MVT: 
<ol class="riferimenti">
	<li>I raccoglitori dovrebbero catturare più prede in aree ad alta densità di prede rispetto a zone a bassa densità di prede.</li>
	<li>I raccoglitori dovrebbero trascorrere più tempo a cercare cibo in aree ad alta densità di prede rispetto a quelle con bassa densità di prede.</li>
	<li>Le bottinatrici dovrebbero avere un tasso di cattura delle prede più elevato nelle zone dense rispetto a quelle più lontane.</li>
	<li>I raccoglitori dovrebbero trascorrere più tempo a cercare cibo in ambienti densi, dove le macchie sono raggruppate, piuttosto che in ambienti sparsi.</li>
	<li>Le bottinatrici dovrebbero lasciare una macchia quando il tasso di cattura è sceso al tasso medio di tutte le chiazze.</li>
</ol>
L'intervallo di tempo tra il momento in cui l'ultima preda viene catturata e il momento in cui il raccoglitore lascia la macchia è noto come Giving-Up-Time, o GUT. Nel contesto dell'MVT, il GUT dovrebbe essere lo stesso in tutte le patch per ogni singolo raccoglitore. Questo è stato testato in un esperimento con cince dal cappuccio nero in una grande voliera alla ricerca di vermi della farina nascosti in pigne artificiali, dove gli uccelli avevano lo stesso GUT per tutti i tipi di chiazze, che era inversamente correlato al tasso medio di cattura per l'intero ambiente 2. 
Più a lungo un organismo trascorre il foraggiamento, più energia spende e più a lungo si espone ai predatori e agli elementi, quindi lo sviluppo di una strategia di foraggiamento ottimale per l'acquisizione di risorse è essenziale per la maggior parte degli organismi. I principi dell'MVT hanno molte applicazioni nella vita reale per promuovere la diversità, la conservazione e persino il comportamento umano.
<h4>Foraggiamento ottimale in un ambiente mutevole</h4>
Dal punto di vista della diversità e della conservazione, l'MVT prevede che le specie possono esistere solo se ci sono macchie per soddisfare adeguatamente il fabbisogno energetico di un organismo, quindi la disponibilità e la distanza tra le risorse è importante per gli organismi che dipendono da esse per la sopravvivenza. La perdita di habitat, l'inquinamento e altri cambiamenti nell'ambiente possono interferire con la capacità di un organismo di foraggiare in modo ottimale, riducendo così la sua idoneità. Così, quando gli habitat di un ecosistema vengono distrutti, vengono rimosse macchie o intere comunità. Questa rimozione limita le risorse disponibili per gli abitanti del resto di un ecosistema. Un minor numero di aree con risorse crea una competizione più intensa e può eliminare alcune specie. Ciò è particolarmente importante per le specie minacciate di estinzione a causa della perdita di habitat che non saranno in grado di soddisfare le loro esigenze di foraggiamento se la maggior parte del loro habitat viene distrutta. 
Gli esseri umani hanno sviluppato una sofisticata conservazione del cibo per limitare le esigenze di foraggiamento, tuttavia ci sono molti altri casi in cui il foraggiamento è necessario, come la ricerca di un alloggio a prezzi accessibili, un lavoro ben retribuito o la ricerca di un appuntamento adatto, tra gli altri. Uno studio recente ha testato le previsioni della MVT utilizzando le capacità di ricerca di informazioni dei medici di medicina generale. Hanno scoperto che i medici di base cercavano in modo ottimale le informazioni quando diagnosticavano un paziente; Si sono spostati rapidamente tra più fonti di informazione e hanno utilizzato sia fonti ad alta densità, come Internet, sia fonti facilmente raggiungibili, inclusi i loro colleghi spesso 3. Allo stesso modo, la teoria del foraggiamento ottimale si applica anche all'economia nel modo in cui i consumatori acquistano o "cercano" prodotti e informazioni quando effettuano un acquisto 4. Questi studi dimostrano come gli esseri umani aderiscano alle previsioni della teoria del foraggiamento ottimale in una varietà di contesti.
<h4>Referenze</h4>
<ol>
	<li>Charnov, E. L. foraggiamento timale: il teorema del valore marginale. Biologia teorica delle popolazioni. 1976, Vol. 9, (129-36).</li>
	<li>John Krebs, John Ryan, Eric Charnov. Caccia per aspettativa o foraggiamento ottimale: uno studio sull'uso dei cerotti da parte delle cince. comportamento animale. 1974, vol. 22, (953-64).</li>
	<li>Mai Dwairy, Anthony C. Dowell, Jean-Claude Stahl. L'applicazione della teoria del foraggiamento al comportamento di ricerca delle informazioni dei medici di medicina generale. Pratica familiare BMC. 2011, vol. 12, 90.</li>
	<li>Wells, V.K. Foraging: un modello ecologico del comportamento dei consumatori? Teoria del marketing. 2012, vol. 2, 12 (117-136).</li>
</ol>

Foraggiamento ottimale

Foraggiamento ottimale
Gli organismi devono acquisire e utilizzare le risorse del loro ambiente per sopravvivere. Mentre il cibo è una delle risorse primarie, gli organismi devono ...

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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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