SOCIAL ORGANIZATION

I. INTRODUCTION

Some animals live in social groups and some live solitary lives. Over evolutionary history, relatively social and non social types have competed in ways that help their reproductive success and thus enable them to produce more offspring. In some species, social life has become the norm but in a large majority of species, solitary life is the norm and solitary species on average leave more descendent offspring.

A. Costs of Social Life

1. Greater conspicuousness to predators

2. Greater transmission of disease and parasites

a. honey bees increase the heat in the hive in response to invasion by a fungal pathogen but this requires time and energy

b. general rule - the larger the group, the greater the risk

3. More competition for food

4. dominant/subordinate relationships. How does this cost energy for both

5. Reproductive interference.

a. increased male vulnerability to___________________________

b. increased female vulnerability to_________________________

 

 B. Benefits of Social Life

1. Most widespread benefit is increased ability to detect predators

a. Dilution

b. _______________________

c. Increased vigilance

d. _______________________

 

2. Gaining immunity against pathogens

3. Improved ability to find food

a. This is best explained by the _______________________________

b. Also learning mechanisms such as negative information in the starlings

4. _________________________________

5. Ability to reduce the reproductive success of others

 

a._______________________________________

b. females can toss the eggs of others or dump their own eggs in others' nests

II. HELPING BEHAVIOR

Social living animals also have the potential to help one another.

A. Types of Interactions

1. The types of interactions are summarized in the table below. Fill in the missing information

B. Mutualism is defined as cooperation between individuals. However, it is not always easy to understand what both might gain as in the case of the long-tailed manakin.

2. they sing duets to attract females and once females arrive, they perform very elaborate displays

a. cartwheel display (see video)

b. butterfly display

3. Only alpha breeds

4. How is this cooperative behavior?

C. Reciprocity - a situation in which individuals help others at personal costs because they will be repaid later for the favor.

2. Cotton top tamarins

a. Special cage with two monkeys in separate compartments (puller and companion)

b. Monkeys had access to a bar that could deliver food either to the companion or the themselves depending on the placement of food

c. Pullers were trained to always pull a bar for food even when it was not on their side.

d. Test - ACTORS were then paired up either with a TRAINED PULLER or a DEFECTOR, an animal that had never been trained to pull. On half the trials, the actor had an opportunity to pull the bar and give food to the trained puller (cooperator) or the defector (noncooperator).

e. What is the prediction derived from the reciprocity hypothesis?

 

 

 

-	TRAINED PULLER	DEFECTOR
ACTOR	-	-
-	-	-

f. Do the data support the reciprocity hypothesis?

 

 

 

2. How did reciprocity evolve?

a. although some primates appear to have the capacity for reciprocity, it is vulnerable to a selfish mutant (accepts help but does not payback) and because defectors harm helpers, it is difficult to imagine how reciprocity might evolve.

b. This is best shown by a game theory model called prisoner's dilemma. Two people commit a crime and are brought in for questioning and are put in separate rooms. They both agree not to snitch on each other. But all sorts of things can happen. Fill in the Table below to understand the prisoner's dilemma and outcomes

	Player B Cooperate	Player B Defect
Player A Cooperate	-	-
Player A Defect	-	-

c. What does this table show?

 

d. This simple game theory model however misses one thing that may help explain the evolution of this behavior. What is that?

 

 

 

e. Vampire Bats as an example - does reciprocal altruism exist in this species? If so, how?