Optimal Foraging Theory (OFT)

Optimal Foraging Theory
Presented By:
Tikesh Kumar
M.Sc Zoology 2nd Semester
Roll No.:- 2180900045
Barkatullah University, Bhopal
Department of Zoology and Applied Aquaculture
Session: 2020–21
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Contents
 Introduction.
 Optimal foraging 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.
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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.
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 Optimal Foraging Theory (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.
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 Building an Optimal 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).
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Figure 1. Energy gain per cost (E) for adopting foraging strategy x

 Optimal diet model (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.
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 Optimal diet model (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 ).
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 Patch Choice (Patch departure rule)
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 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.

 Example of Optimal 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.
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Figure 2. longer traveling time results in larger
optimum load.

 Conclusion
 The optimal 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.
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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.
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