Questions in the study
of foraging behavior
----------------------------1. How do animals select prey?
2. When should animals leave one feeding
site and go on to another?
3. How should animals divide their time
between food-gathering and other
activities?
10
_
LOAD
_
7
4
_
_
1
|
|
Travel Time
|
|
|
Searching Time
|
TIME
10
_
LOAD
_
7
4_
Y1
_
1
|
|
Travel Time
|
X1
|
|
Searching Time
|
TIME
10
_
Load/Time is maximized at X2,Y2
LOAD
_
7
Y2
4_
_
1
|
|
Travel Time
|
|
X2
|
Searching Time
|
TIME
10
_
LOAD
_
7
4
Long optimum
_
Short optimum
_
1
|
|
Travel Time
|
X1
|
X2
|
Searching Time
|
TIME
_
Load _
_
_
|
|
|
|
|
|
Round trip travel time
STEPS IN ANALYSIS
1. Determine relevant variables through
observation
2. Establish (you think) how these
variables interact
3. Make predictions
4. Test
Crows feeding on whelks
Select the largest whelks available
Fly roughly 5.5 m high to drop the whelk
on the rocks below
If whelk doesn’t break open, select the
same 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
Intake_
of
aquatic
_
plants
(gm)
Energy constraint
_
Sodium constraint
_
Rumen
constraint
|
|
|
|
|
|
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
4 pellets x
0.5
0.5
average yield of 2
Testing Conditions
Food Choice
(reward x probability)
Starved for 1 hour
2 pellets x 1.0 =
avg. 2
Starved for 4 hours
(0 pellets x 0.5) +
(4 pellets x 0.5) =
avg. 2
Testing Conditions
Food Choice
(reward x probability)
Starved for 1 hour
2 pellets x 1.0 =
avg. 2
Starved for 4 hours
(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.
Components of Life Histories:
Where the trade-offs occur
• Growth and Development
• Reproduce Early or Delay
• Clutch Size vs. Clutch Number
• Offspring Size and Offspring Number
• Offspring Size and Parental Care
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
House Mouse African elephant
2 months
11 - 20 years
Salmon
3-6 years
Life history traits – characteristics of an individual
that influence survival and reproduction
Number of offspring produced
House Mouse African elephant
5-8 young
every month
1 calf every
3-8 years
Salmon
1,500 to
8,000 eggs
once
Life history traits – characteristics of an individual
that influence survival and reproduction
Number of reproductive events
House Mouse
~6-12
African elephant
~3 - 10
Salmon
1
Life history traits – characteristics of an individual
that influence survival and reproduction
Lifespan
House Mouse
~2 years
African elephant
60 - 70 years
Salmon
3-6 years
Reproductive strategies
K-strategists:
•long lived
•produce few offspring
•parental care
Population is controlled by density-dependent
limiting factors - e.g. food
Reproductive strategies
r-strategists:
•small
•short life
•no parental care
•many offspring
Gypsy moth caterpillars
Population is controlled by densityindependent limiting factors: weather,
pond drying
12-Arm Radial Maze
2.1m
_
80
%
_
Corr.
40
_
_
|
|
|
.25
.50
1
|
|
2
4
Delay (hours)
|
8
12
5
4
9
10
8
11
7
1
3
6
2
12
Food-storing Birds
Clark’s nutcracker:
33,000 seeds, 7,500 sites
Pinon jays: 22,000 seeds,
clumped
Scrub jays: 6,000 seeds
Cache retrieval in corvids
% correct, 1st 4 choices
100
Nutcracker
90
Pinyon jay
80
70
Scrub jay
60
Mexican jay
50
0
2
4
6
8
10
12
Block (avg of 5 trials)
Kamil et al. 1994
_
% 80
correct
_
60
40
_
_
20
Nutcrackers
Pinyon jays
Scrub jays
Mexican jays
| | | | | | | | | | |
50 100 150 200 250 300
Retention interval (min)
| |
Meadow Vole:
Polygynous
Female
ranges
Male
range
Prairie Vole:
Monogamous
?
?
Olson et al. 1995
Strict behaviorism:
Any stimulus can, through conditioning, be associated with
any response or reinforcer
Learning is a general process phenomenon:
All associations are learned equally easily
All 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
BECAME SICK
Avoided saccharine,
But no fear of light or
noise
SHOCKED
Fear reaction to light and
noise, but no aversion to
saccharine
(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 and
behaviors of animals so that they optimize
(as near as possible) the exploitation of their
environment
-- 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