L3. Group Living

Question 1

Why did group living evolve?

Answer 1

Evolved as a result of fitness benefits to individuals
-A genetic tendency to group with others gave individuals a fitness advantage, and the tendency became more common in the population

Question 2

What are two selective pressures hypothesised to influence whether animals live in groups?

Answer 2

1. Predator / Predation avoidance
2. Resource acquisition and defence

These are not mutually exclusive pressures

Question 3

What are the benefits of group living?

Answer 3

-Increased chance of avoiding predation
-Increased vigilance
-Dilution of risk
-Predator confusion
-Group defence

Question 4

How does increased vigilance affect predators?

Answer 4

-For most predators, success depends on surprise
-If spotted, their chance of success is low
-Studies have found that larger groups are better at detecting approaching predators

Question 5

What occurs to vigilance time as group sizes increase?

Answer 5

-Individuals can decrease their vigilance, with a larger group
-Open to cheating

Question 6

How does a large group benefit an individual?

Answer 6

-The individual in the group may not need to detect a predator to be warned of the threat
-Depends on information transfer

Question 7

What is the cheating hypothesis surrounding group living?

Answer 7

-If group is large and 100% vigilance occurs, it may be beneficial for an individual to stop being vigilant and spend more time feeding
-However this cheating does not appear to occur.

Question 8

What are the direct benefits for vigilant behaviour for the individual?

Answer 8

-Predators may prefer to attack non-vigilant individuals
-Spotting the predator yourself may allow a quicker response
-Being vigilant may allow you to react more quickly to the signal of another group member

Question 9

Explain dilution of risk.

Answer 9

-Living in groups- dilute the risk of being killed by a predator
-Better chance that another group member will be attacked instead
-Probability of survival increases with group size

Question 10

What stops dilution risk?

Answer 10

-If there is a linear relationship between group size and probability of detection by a predator
-Predators can attack all members of a group

Question 11

What is an example of group dilution risk?

Answer 11

-Water skaters sit on surface water get attacked by fish from below
-Attack rate by fish is similar for groups of different sizes
-Observed and predicted lines in close agreement
-Decline in attack rate with group size due to dilution

Question 12

What is predator confusion?

Answer 12

-Predators may find it difficult to single out an individual in a group to attack
-Individuals receive greater protection in more compact groups

Question 13

What makes predator confusion more effective?

Answer 13

-When all members of the group are more alike
-Individuals that stand out may suffer more predation (the oddity effect)

Question 14

What is group defence?

Answer 14

-Many bird species mob predators
-Combined response of group members increases the effectiveness of the behaviour
-Experimental nests put near bird colonies suffer reduced predation compared to isolated nests

Question 15

What are other benefits to group living?

Answer 15

Increased chances of
-Finding food
-Co-operative hunting
-Defending food
-Easier to find a mate, conservation of heat and water
-Reducing energetic costs of moving

Question 16

What is a benefit and disadvantage to finding food as a group?

Answer 16

-Easier and quicker to find food
-However individuals that feed in groups suffer a disadvantage through competition with other group members

Question 17

How do predators benefit from group living?

Answer 17

-Can catch prey that is too large for one animal alone
-Catch prey that is too elusive for one animals alone
-Separate an individual from a group
-Can defend a carcass after a kill eg. lions

Question 18

What disadvantages are there to group living?

Answer 18

-Predation, bigger groups are less conspicuous - large shoals easier to detect by sonar from cetaceans
-Greater competition for food
-Increase in parasite burden and disease transmission
-Infanticide from unmated males eg. swallows

Question 19

What is kleptoparasitism?

Answer 19

Food discovered by one animal is stolen by another

Question 20

What are the costs and benefits to kleptoparasitism?

Answer 20

-Some individuals gain while others lose
-Risk of injury to both parties
-Lost opportunities to find food by conventional means
-Risk of losing prey

Question 21

How can parasite burden affect group living?

Answer 21

-Cliff swallows nest colonially, however bigger colonies have higher numbers of swallow bugs on hatchlings (ectoparasite)
-Bugs have negative effect on nestling growth.

Question 22

How does group living affect disease transimission?

Answer 22

2010 study on guppies (Richards)
-Single sex shoals
-Fish were infected with Gyrodactylus turnbulii
-Female guppies shoaled more than males
-Females passed on infection more than males
-Increased shoaling, increased transmission

Question 23

What is a reproductive cost to group living?

Answer 23

-More competition between males
-Increase in aggression
-Monopolisation of females by a few males
-Cuckoldry

Question 24

What is cuckoldry?

Answer 24

Potential cost to males that provide parental care
Females may be fertilised by males other than their mates

Question 25

Describe the evolution of group living experiment with schooling guppies.

Answer 25

-Guppies that school are less successful at competing for food
-1950s 200 guppies were transferred from predator-rich stream A to predator-poor stream B
-30 years later the guppies were collected from A, B and C

Question 26

What was the results of the guppy group living experiment?

Answer 26

-Guppies from B were less likely to shoal than guppies from A
-Guppies from C had more of a tendency to shoal than guppies from B

Question 27

What did the guppy group living experiment demonstrate?

Answer 27

-Evolutionary response based on short-term costs and benefits of living in groups
-Initial decrease in schooling behaviour in absence of predators
-Subsequent increase in schooling behaviour due to predation pressures
-Evolutionary responses occurred within approximately 100 generations

Question 28

What is the optimal group size?

Answer 28

Is when costs and benefits with group size that allows individuals to maximize fitness
-Where the net benefit is maximised

Question 29

What behaviour do sparrows do when foraging?

Answer 29

-When food is found, sparrow calls to attract others
-More likely to call if food is divisible
-More likely to feed if joined by another
-Calls less as group size increases

Question 30

How does spatial positioning affect the benefits of being in a group?

Answer 30

-Food availability and quality may be higher for individuals in peripheral and front positions
-Energy expenditure may lower at rear of group
-Peripheral members may be at higher risk of predation
-Breeding success higher for those in centre

Question 31

What is co-operative breeding?

Answer 31

-Offspring stay to help raise siblings
-Forfeit or delay chance to breed independently

Question 32

What are some constraints on independent breeding?

Answer 32

-Shortage of suitable breeding habitats
-Reduced survival probability following dispersal
-Reduced probability of finding a mate