Optimal Foraging Theory (OFT)

Optimal Foraging Theory (OFT)

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  Optimal Foraging Theory PresentedBy: Tikesh Kumar M.Sc Zoology 2nd Semester Roll No.:- 2180900045 Barkatullah University, Bhopal Department of Zoology and Applied Aquaculture Session: 2020–21 1
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  Contents  Introduction.  Optimalforaging theory (OFT).  Building an optimal foraging model.  Optimal diet model (Prey choice model).  Patch Choice (Patch departure rule).  Example of optimal foraging in bees.  Conclusion.  Reference. 2
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   Introduction: Foraging Foraging:- Foraging is searching for wild food resources.  Foraging Theory:- Branch of behavioral ecology that deals with the foraging behavior of the organisms with respect to their environment.  Optimal Foraging Theory (OFT):- Behavioral ecology model that helps predict how an animal behaves when searching for food.  Marginal Value Theorem (MVT):- Optimality model that describes the behavior of an optimally foraging individual in a system where resources are located in discrete patches separated by areas with no resources. 3
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   Optimal ForagingTheory (OFT)  Formulated by MacAurthur-Pianka (1966).  It predicts how an animal behaves when searching for food.  It states “to maximize fitness, an animal adopts a foraging strategy that provides the most benefit (energy) for the lowest cost, maximizing the net energy gained.”  It assumes that most economically advantageous foraging pattern will be selected for a species through natural selection.  OFT helps predict the best strategy that an animal can use to achieve this goal. 4
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   Building anOptimal Foraging Model  Optimal foraging model generates quantitative predictions of how animals maximize their fitness while they forage.  The model building process involves identifying the currency (maximum food per unit time), constrains (environmental) and appropriate decision rule for the forager (organism‟s best foraging strategy). 5 Figure 1. Energy gain per cost (E) for adopting foraging strategy x
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   Optimal dietmodel (Prey choice model)  The model predicts that foragers should ignore low profitability prey items when more profitable items are present and abundant.  Profitability of prey item depends on:  E :- amount of energy that a prey item provides to the predator.  Handling time (h):- time it takes the predator to handle the food.  Search time (S):- time it takes the predator to find a prey.  Profitability of prey item:- E/h. 6
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   Optimal dietmodel (Prey choice model)  Choice between big and small prey:  Prey1 with energy value E1 and handling time h1, and small Prey2 with energy value E2 and handling time h2 .  If it is assumed that big prey 1 is more profitable than small Prey 2, then E 1 /h 1 > E 2 /h 2. (Should consume for higher profitability).  However, if the animal encounters Prey 2, it should reject it to look for a more profitable Prey 1, unless the searching time for Prey 1 is too high.  The animal should eat Prey 2 only if E 2 /h 2 > E 1 /(h 1 +S 1 ). 7
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   Patch Choice(Patch departure rule) 8  The forager changes the track in patch and habitat quality to save time to invest time more effectively on other patches.  Departure from a prey patch is one of the key factors determining its foraging success.  ‘W’ representing the time a predator is „willing‟ to invest in the patch.  As long as no prey are captured, „W‟ declines and when it drops below a critical level the patch is abandoned.
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   Example ofOptimal Foraging in bees.  Wolf and Schmid-Hempel (1989) showed, by experimentally placing varying weights on the backs of bees, that the cost of heavy nectar is so great that it shortens the bees lifespan.  The total amount of nectar foraged increases linearly with time spent in a patch.  By maximizing energy efficiency, the bees were able to avoid expending too much energy per trip and are able to live long enough to maximize their lifetime productivity for their hive. 9 Figure 2. longer traveling time results in larger optimum load.
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   Conclusion  Theoptimal foraging theory predicts that animal will forage in a way that will maximize its net yield of energy. The foraging strategies tend to increase the expected reward in the next prey visited, by avoiding patch which have been recently visited, by choosing more rewarding individual patch. 10
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   Reference  Stephens,D.W., Brown, J.S., and Ydenberg, R.C. (2007). Foraging: Behavior and Ecology.  Wolf, T. J., & Schmid-Hempel, P. (1989). Extra loads and foraging life span in honeybeeworkers. The Journal of Animal Ecology.  Charnov, E. L. (1976). Optimal foraging: the marginal value theorem. Theoretical Population Biology. 11
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