1. The document presents information on foraging ecology, including optimal foraging theory, the marginal value theorem, and central place foraging. It discusses concepts like patch departure rules, prey choice models, and foraging by pollinators. 2. Key optimal foraging concepts discussed include prey profitability based on energy gained versus handling time, and the marginal value theorem which describes when an animal should leave a patch based on diminishing returns. 3. Central place foraging theory is described as looking at how foraging time is impacted by travel time between patches and a central location like a nest.

1. 1
Power point presentation
On
Foraging ecology
Name- Vedant Gautam
PhD 1ST year
PM-22038
Mycology and Plant Pathology
Subject- Insect ecology and Diversity
(ENT-603)
Submitted to
Dr. P.S. Singh (Professor)
Dr. R.S. Meena ( Asst. professor)
Department of entomology

2. Contents
Foraging And Foraging Ecology
Optimal Foraging Theory
Marginal Value Theorem
Patch Departure Rule
Central Place Foraging
Mean Variance Relationship
Foraging By Pollinators
Nutritonal Ecology

3. INTRODUCTION
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.

4. 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.

5. 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.

6. Optimal diet model (Prey choice model)
Choice between big and small prey:
 Prey, with energy value E, and handling time h₁, and small Prey,
with energy value E, and handling time h₂.
 If it is assumed that big prey, is more profitable than small Prey,,
then E₁/h,> E2/h2 (Should consume for higher profitability).
 However, if the animal encounters Prey 2, it should reject it to look
for a more profitable Prey, unless the searching time for Prey, is too
high.
 The animal should eat Prey, only if E,/h2>E₁/(h,+S₁).

7. an objective function, what the animal want to maximize, in this case
energy over time as a currency of fitness
as the unit that is optimized by the animal.
net energy gain per unit time.
net energy gain per digestive turnover time instead of net energy gain
per unit time.
CURRENCY

8. Are hypotheses about the limitations that are placed on an animal.
Due to features of the environment or the physiology of the animal
and could limit their foraging efficiency.
For example-:
 The time that it takes for the forager to travel from the nesting
site to the foraging site is an example of a constraint.
 The maximum number of food items a forager is able to carry
back to its nesting site is another example of a constraint.
Constraints

9. OPTIMAL DECISION RULE
Model's prediction of what will be the
animal's best foraging strategy or set of
choices under the organism's control
for examples
optimal number of food items that an animal should carry back to its nesting
site.
the optimal size of a food item that an animal should feed on.
Figure, shows an example of how an optimal decision rule could be determined
from a graphical model. The curve represents the energy gain per cost (E) for
adopting foraging strategy x. Energy gain per cost is the currency being
optimized. The constraints of the system determine the shape of this curve. The
optimal decision rule (x*) is the strategy for which the currency, energy gain per
costs, is the greatest.

10. (B) Marginal Value Theorem (MVT)
The marginal value theorem is an optimality model that usually
describes the behavior of an optimally foraging individual in a system
where resources (often food) are located in discrete patches separated
by areas with no resources.
Due to the resource-free space, animals must spend time traveling
between patches.
The MVT can also be applied to other situations in which organisms
face diminishing returns.

11. This may be because the prey is being depleted, the prey begins
to take evasive action and becomes harder to catch, or the
predator starts crossing its own path more as it searches.
This law of diminishing returns can be shown as a curve of energy
gain per time spent in a patch.
The curve starts off with a steep slope and gradually levels off as
prey becomes harder to find. Another important cost to consider is
the traveling time between different patches and the nesting site.
An animal loses foraging time while it travels and expends energy
through its locomotion.
(B) Marginal Value Theorem (MVT)

12. In this model, the currency being optimized is
usually net energy gain per unit time.
The constraints are the travel time and the
shape of the curve of diminishing returns.
Graphically, the currency (net energy gain per
unit time) is given by the slope of a diagonal
line that starts at the beginning of traveling time
and intersects the curve of diminishing returns.
In order to maximize the currency, one wants
the line with the greatest slope that still touches
the curve (the tangent line). The place that this
line touches the curve provides the optimal
decision rule of the amount of time that the
animal should spend in a patch before leaving.
(B) Marginal Value Theorem (MVT)

13. Time
Travel Time Search Time in Patch
Slope = Energy gain/Time
Point of
diminishing
returns
Time to leave!
Another way to look at this (when there is only 1 patch type)
Marginal Value Theorem
Which strategy yields the
greatest E/T?

14. Time
Travel Time Search Time in Patch
What if patches are denser (travel time is less)?
Leave earlier when
travel time is
shorter.
Sparse
Dense
Marginal Value Theorem

15. 1. Leave at a fixed MV (indep. of patch quality
2. Stay in higher quality patches longer
3. Skip patches in which dg/dt|t=0 < En*
4. As the density of patches increase…
a. Reduce residency time
b. Drop low quality patches from diet
5. Variants:
a. Giving up density (uniform among patches)
b. Giving up time (time since last prey taken)
Predictions of MVT:

16. Patch Choice (Patch departure rule)
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.

17.  Describes the behavior of a forager whose prey is concentrated
in small areas known as patches with a significant travel time
between them.
 The model seeks to find out how much time an individual will
spend on one patch before deciding to move to the next patch.
To understand whether an animal should stay at a patch or move
to a new one, think of a bear in a patch of berry bushes.
Patch selection theory

18. Patch selection
 Consider a forager moving among many patches during a foraging
bout (rodent among seed caches, pollinator among flowers, etc.)
 Which patches does it feed in?
 For how long? (when does it leave?)
 How are these decisions altered by patch density?
 Or the quality of other patches?

19. GOAL: Maximize rate of net energy gain (intake – losses /
time)
Charnov (1976)
Patch selection

20. Cumulative
energy
intake
Patch selection

21. Marginal Value Theorem:
Leave when: dg/dT = En*
Patch selection

22. • This theory is a version of the patch model. This model describes
the behavior of a forager that must return to a particular place to
consume food, or perhaps to hoard food or feed it to a mate
or offspring.
• Chipmunks are a good example of this model. As travel time
between the patch and their hiding place increased, the
chipmunks stayed longer at the patch.
Central Place Foraging

23. FORAGING BY POLLINATORS

24. AGRICULTURE AND POLLINATOR
POLLINATOR
MANAGED
POLLINATOR
NATURAL
POLLINATOR
INCREASED AGRIULTURAL
PRODUCTIVITY
SOIL CONSERVATION AND
SOIL FERTILITY
IMPROVEMENT
ENVIRONMENT
CONSERVATION AND
MAINTAINANCE OF
BIODIVERSITY
INCREASED INCOME
AND FOOD SECURITY
IMPROVED LIVILIHOOD
Pratap, 2011

25. Diversity of insect pollinators
Social bees
Solitary/pollen bees (Sand bees, Digger bees, Leaf cutter bees,
Sweet bees, Carpenter bees)
Parasitic bees
Hover flies /flower fly (Diptera)
Moths, Butterflies, beetles and housefly and other insects

26. Foraging by honey bee
 For pollen and nectar from blooming plant.
 Also for water
 Pollen- protein
 Nectar- mineral, vitamin and energy
 Time of foraging- 7-8 a.m.
 Also depends on the sunshine and temperature
 Optimum temperature-25 27 degree celcius

27. Language in honey bee
ROUND DANCE WAIG-TAIL DANCE

28. Insect nutrition
NUTRITION : The process of nourishing or being nourished,
especially the process by which a living organism assimilates
food and uses it for growth and for replacement of tissues.
Insects also respond to imbalance diet.

29. Monophagous Oligophagous Stenophagous Polyphagous
Herbivore Carnivore

30. Nutrient requirements
Nutritional requirement an be defined as chemical fators essential
to the adequacy of ingested food.
Insects require nutrients similar to that of other animals but in
specific quantity.
Principle of insect nutrition
 Principle of sameness
 Principle of nutrient proportionality
 Principle of cooperating supplement

31. Proteins & aminoacids
 Insect require complete protein for growth.
 For eg. T confusum larvae did not grow in the absence of zein
or gliadin, Arg ,His ,Leu ,Iso ,Lys ,Met ,Phy ,Thr ,Try ,Val –AA.
 Needed for maturing eggs ,secretion of JH , optimal growth
,morphogenesis , neurotransmitters and development.
E.g. – tyrosine – sclerotization
glutamate - neurotransmitter

32.  Major source of energy.
 Act as feeding stimulant – sucrose.
 Not essential , can be synthesized from lipids and proteins.
 Tribolium can use starch, mannitol, raffinose, sucrose, maltose,
cellobiose.
 Worker honey bee needs carbohydrate before pupation.
 Lepidoptera, Orthoptera , Homoptera use it as flight energy.
 Most insects are unable to use cellulose .
Carbohydrate

33.  Can be synthesized except sterols.
 Sterol is the precursor of 27-carbonecdysteroid molting hormone.
 e.g –Lucilia sericata
 Sterol deficiency reduces 80% hatching in housefly eggs.
Lipids and sterols

34. Insects cannot synthesize vitamines.
 Require thiamine, riboflavin, nicotinic acid, pyridoxine,
pantothenic acid, folic acid and biotin.
 Act as cofactors of enzymes.
 Biotin – synthesis of fatty acid, pyruvate carboxylase.
 Folic acid – nucleic acid synthesis.
 Vitamin A – normal morphology of compound eyes.
 Vitamin E – reproduction
 Ascorbic acid – normal growth &
development.
Vitamins

35.  Inadequately known.
 Need - Na, K, Ca, Mg, Cl, P.
 Enzyme cofactor –
e.g–Mo-purine metabolism, Xanthine dehydrogenase enzyme
 Phytophagous insects need more K and trace amount of Na.
Minerals

36.  Chemical compound affecting insect feeding.
May be –
 Nutritional components
 Non-nutritional allelochemicals
 Hexose sugars and sucrose – phagostimulant for leaf feeding
insects.
 Pieris larvae – mustard oil glucoside.
 A defensive chemical in plant –
 e.g – cucurbitacin, mulberin
Phagostimulant

37. 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.

38.  Wolf, T. J.; Schmid-Hempel, P. (1989). "Extra Loads and Foraging Life Span
in Honeybee Workers". The Journal of Animal
Ecology. 58 (3):943. JSTOR 5134.doi:10.2307/5134.
 Schmid-Hempel, P.; Kacelnik, A.; Houston, A. I. (1985). "Honeybees maximize
efficiency by not filling their crop". Behavioral Ecology and Sociobiology. 17:
61.doi:10.1007/BF00299430
 Hempptinne et al,1993. Optimal foraging by hoverflies (Diptera: Syrphidae)
and ladybirds (Coleoptera: Coccinellidae): Mechanism Eur. J. Entomol. 90 (4):
451-455.
 Cartar RV. 1992. Morphological senescence and longevity: an experiment
relating wing wear and life span in foraging wild bumble bees. J. Anim.
Ecol. 61, 225–231. (doi:10.2307/5525)
 Charnov (1976) Optimal foraging . The marginal value theorem. Theoritical
population biology 9,129-136.
References

39. • Werner, E. E.; Hall, D. J. (1974). "Optimal Foraging and the Size Selection
of Prey by the Bluegill Sunfish (Lepomis macrochirus)". Ecology. 55 (5):
1042. JSTOR 1940354.doi:10.2307/1940354
• Richardson, H. & Verbeek, N. A. M. 1986: Diet selection and optimization
by northwestern crows on Japanese littleneck clams. Ecology 67, 1219—
1226.
• Richardson, H. & Verbeek, N. A. M. 1987: Diet selection by yearling
northwestern crows (Corvus caurinus) feeding on littleneck clams
(Venerupis japonica). Auk 104, 263—269.
• Glover, S. M. 2009. Propaganda, Public Information, and Prospecting: Explaining
the Irrational Exuberance of Central Place Foragers During a Late Nineteenth
Century Colorado Silver Rush. Human Ecology 37, 519-531.
References