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Questions in the studyQuestions in the studyof foraging behaviorof foraging behavior
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1. How do animals select prey?
2. When should animals leave one feedingsite and go on to another?
3. How should animals divide their timebetween food-gathering and other activities?
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LOAD
1
4
7
TIMETravel Time Searching Time
10
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LOAD
1
4
7
TIME
Travel Time Searching Time
10
X1
Y1
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LOAD
1
4
7
TIME
Travel Time Searching Time
10
X2
Y2
Load/Time is maximized at X2,Y2
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LOAD
1
4
7
TIME
Travel Time Searching Time
10
X1 X2
Short optimum
Long optimum
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Load
Round trip travel time
STEPS IN ANALYSISSTEPS IN ANALYSIS
1. Determine relevant variables throughobservation
2. Establish (you think) how thesevariables interact
3. Make predictions
4. Test
Crows feeding on whelks
Select the largest whelks available
Fly roughly 5.5 m high to drop the whelkon the rocks below
If whelk doesn’t break open, select thesame whelk to drop again
Patches
Problem: When to leave a patch?
Constraints that affect “optimal”foraging behavior
1. Physiological constraints
2. Motivational constraints
3. Ecological constraints
4. Life history constraints
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Energy constraint
Sodium constraint
Rumenconstraint
Intakeofaquaticplants(gm)
Intake of terrestrial plants (gm)
Constraints that affect “optimal”foraging behavior
1. Physiological constraints
2. Motivational constraints
3. Ecological constraints
4. Life history constraints
Food Choice (reward x probability)
reward probability 2 pellets x 1.0 average yield of 2
0 pellets x 0.54 pellets x 0.5 average yield of 2
Testing Conditions
Starved for 1 hour
Starved for 4 hours
Food Choice (reward x probability)
2 pellets x 1.0 = avg. 2
(0 pellets x 0.5) +(4 pellets x 0.5) = avg. 2
Testing Conditions
Starved for 1 hour
Starved for 4 hours
Food Choice (reward x probability)
2 pellets x 1.0 = avg. 2
(0 pellets x 0.5) +(4 pellets x 0.5) = avg. 2
Constraints that affect “optimal”foraging behavior
1. Physiological constraints
2. Motivational constraints
3. Ecological constraints
4. Life history constraints
Constraints that affect “optimal”foraging behavior
1. Physiological constraints
2. Motivational constraints
3. Ecological constraints
4. Life history constraints
Life History Evolution
The study of how individuals allocate, throughout life, time and energy to various fundamental activities, such as growth and reproduction
Life Histories: An inherent trade-off
Investment in any one activity limits an animal’s ability to invest in others.
As applied to reproduction, a parent’s dilemma: investment in any one offspring limits an animal’s ability to invest in others.
• Growth and Development
• Reproduce Early or Delay
• Clutch Size vs. Clutch Number
• Offspring Size and Offspring Number
• Offspring Size and Parental Care
Components of Life Histories: Where the trade-offs occur
Life histories: the major questions
Why do organisms age and die?
How many offspring should an individual produce in a given time?
How big should each offspring be?
Life history traits – characteristics of an individual that influence survival and reproduction
Age at maturity
11 - 20 years 3-6 years
SalmonAfrican elephant
2 months
House Mouse
Life history traits – characteristics of an individual that influence survival and reproduction
SalmonAfrican elephantHouse Mouse
1 calf every 3-8 years
1,500 to 8,000 eggs
once
5-8 young every month
Number of offspring produced
Life history traits – characteristics of an individual that influence survival and reproduction
SalmonAfrican elephantHouse Mouse
Number of reproductive events
~3 - 10 1~6-12
Life history traits – characteristics of an individual that influence survival and reproduction
SalmonAfrican elephantHouse Mouse
Lifespan
60 - 70 years 3-6 years~2 years
K-strategists:K-strategists:
•long lived•produce few offspring•parental care
Reproductive strategies
Population is controlled by density-dependent
limiting factors - e.g. food
Gypsy moth caterpillars
r-strategists:•small•short life•no parental care•many offspring
Reproductive strategies
Population is controlled by density-independent limiting factors: weather, pond drying
2.1m
12-Arm Radial Maze
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| | | | | | .25 .50 1 2 4 8 12
80
40
%Corr.
Delay (hours)
1
2
3
45
6
7
8
9
10
11
12
Food-storing Birds
Clark’s nutcracker: 33,000 seeds, 7,500 sites
Pinon jays: 22,000 seeds, clumped
Scrub jays: 6,000 seeds
0 2 4 6 8 10 1250
60
70
80
90
100
% c
orre
ct, 1
st 4
cho
ices
Block (avg of 5 trials)
Nutcracker
Pinyon jay
Scrub jay
Mexican jay
Cache retrieval in corvids
Kamil et al. 1994
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40
60
80%correct
NutcrackersPinyon jaysScrub jaysMexican jays
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Retention interval (min)
Meadow Vole:Polygynous
Prairie Vole:Monogamous
Femaleranges
Male range
Olson et al. 1995
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Strict behaviorism:
Any stimulus can, through conditioning, be associated withany response or reinforcer
Learning is a general process phenomenon:All associations are learned equally easilyAll responses are reinforced equally easily
Biological constraints on learning
Saccharine taste + lights + noise
BECAME SICK SHOCKED
(Garcia & Koelling 1966)
Biological constraints on learning
Saccharine taste + lights + noise
Avoided saccharine,But no fear of light or noise
Fear reaction to light and noise, but no aversion to saccharine
BECAME SICK SHOCKED
(Garcia & Koelling 1966)
Summary: Economic decisions
Increasing evidence that animals make “calculations” when foraging
-- make adaptive “choices” among alternative foods-- estimate past rates of return and compare them
with current rates
Summary: Memory
1. Natural selection has shaped the minds andbehaviors of animals so that they optimize(as near as possible) the exploitation of theirenvironment
-- species differences in memory-- memory of a very specific sort-- species differences in the brain structures
that support memory-- sex differences, too-- differences in the kind of associations that
are formed