questions in the study of foraging behavior ----------------------------- 1.how do animals select...

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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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