Living in Groups

Question 1

What are 3 costs associated with living in groups?

Answer 1

Predation costs

• Increased conspicuousness
• Increased profitabilty for predators

Foraging costs
- Competition

Question 2

What are six benefits associated with living in groups?

Answer 2

Predation benefits

• Vigilance
• Dilution effect
• Cover (individuals in centre are covered by individuals at the edge)
• Group defense

Foraging benefits

• Finding food more often (eg. osprey catching fish, others in group see where he’s flying from and head in that direction)
• Catching difficult prey (different roles, mobbing etc.)

Question 3

What are two ways the optimal group size might vary?

Answer 3

• Varies among types of individuals (eg. aggressive or shy)
• Group size for an individual might vary from evolutionary stable strategy vigilance (eg. how much the population looks up, decreasing with group size). What’s optimal for an individual may be different than the evolutionarily stable strategy vigilance model.

Question 4

How do aposematic species differ from cryptic species in terms of the predation costs of being in a group?

Answer 4

Aposematic species don’t have the added consequence of increasing conspicuousness, because this only acts to drive off predators more effectively. They are not trying to be hidden.

When cryptic species group, the become much more conspicuous.

Question 5

Why do lone starlings or pigeons look up a lot as they’re foraging?

Answer 5

Because they are looking out for hawks. In larger groups, there was a lower cost of looking up to be vigilant. They look up less with greater group sizes.

This is a predation benefit of being in a group.

Question 6

What keeps birds from free loading off of other birds in terms of allowing other birds to be vigilant?

Answer 6

Their is a cost to taking attention away from predators. Predators are more selective to prey that are not paying attention.

Question 7

Why would a whole bunch of female birds share 1 male (polyandry)?

Answer 7

Hypothesis: The females nest together as a form of dilution or cover or nest defense (group predation benefits)

Question 8

How might cover, as a group benefit, be tested?

Answer 8

Look at how much prey was taken from centre of group, and how much from edges.

Question 9

How might group defense, as a group benefit, be tested?

Answer 9

Have nests with eggs (or other resource) with living animals and some with no animals.

If more eggs are broken in nests with no living animal, than you can propose that the predation is prevented by defense.

Question 10

How can gulls flying over fish willy nilly (no cooperation) increase the individual catch rate with greater group size?

Answer 10

A single gull causes a fish to flee. More gulls cause fish to ‘flush’ towards each other.