Living in Groups II

Question 1

What are information centers? (foraging) Why tell others your info (2 reasons)? What are the two examples of information centers?

Answer 1

1. Typically bird roosts or nesting colonies
2. If food is rare but abundant when found, could be an ESS to recruit others to help find it (such as in bonanzas).

Reduce predation risk at food site from other foragers.

3. Ravens, house sparrows

Question 2

Elaborate on the raven information centers. Why do they form groups? What are the two ways cooperators are recruited? What are the steps ravens take when they find good food (carcass)? What was the bead experiment that demonstrated roosting in ravens?

Answer 2

1. Juveniles form groups to take carcasses from adults (who will defend against 1-2, but leave at ~6)
2. Loud call when carcass is located, and at the communal roost
3. Follow knowledgeable bird ==> knowledgeable bird initiates dawn departure (suggesting advertising location)
4. Sheep/hare carcasses + color-coded beads: noticed that colors from one carcass accumulated in specific locations in roost (foraging groups roost together) AND colors increased over time (recruitment for foraging, then also into the roost)

Question 3

Elaborate on house sparrow information centers. How do they inform? How was this demonstrated?

Answer 3

1. Selectively - when food is easily shared
2. Pile of bread crumbs = chirrup to recruit while single bread = no call

Question 4

What is a coordinated hunt (better prey capture/foraging)? What are two examples? In the wing formation, what is the implication of specialization seen in this species?

Answer 4

1. Prey is efficiently captured when preds hunt in groups
2. Zebras kick, so hyenas need a group. Hyenas will chase zebras up to 3km then nip at one lagging behind.

2) Lionesses have a formation with “wing” animals (direct) and central animals (attack/largest)

3. Specialization means that the hunt goes better if the lionesses are in their preferred positions

Question 5

What does it mean to have panicked prey (better prey capture/foraging)? What is an example?

Answer 5

1. This means that multiple predators cause large groups of prey to become panicked, going in random directions and either separating from the group or losing coordination with them.
2. Multiple jack fish attacking a fish school

Question 6

What were the two main reasons found for schooling to evolve (guppies)? What determines predator inspection shoal size? What is the implication of this?

Answer 6

1. Familiarity - females guppies shoal with known individuals BUT only in small populations where recognition is more likely
2. Predator inspection - groups are formed and sent to go look at the predator to determine threat
3. Average shoal size determines inspection group size
4. Individuals share the risk of predator inspection more when overall predation risk is high

Question 7

What is the difference between males and females in guppy schooling? Why do males school? Why does this work better than the safe option?

Answer 7

1. Males school less than females
2. Go with predator inspection groups (primarily female) to mate with females.
3. Works better because the male can skip the courtship dance while the female is busy trying to make sure she doesn’t die.

Question 8

What are we referring to when we refer to group size and skew? Where do better individuals typically go? What is one way that the hierarchy is maintained between individuals in the same group?

Answer 8

1. Indvs. in a group are different and therefore differ in the value/benefits they bring to the group
2. Middle of group
3. Subs will regulate what they take so doms don’t kick them out

Question 9

Name an example of how group size/skew works in coral-dwelling gobies. Explain how the hierarchy is determined (1) and maintained (1). How is sex determined? What are the two scenarios for which this happens?

Answer 9

1. Coral-dwelling goby (biggest = best and only the bestest breed)
2. Determined b/c lower is 93% of higher’s body weight

Maintained: Subs refusing food so they aren’t evicted.

3. Socially
4. 1) breeder male dies = largest female –> male

2) Male joins group = smaller one will change –> female

Question 10

What questions are asked for group decision making? What is the answer? What are two examples? What are three scenarios for fish schools?

Answer 10

1. Where do individuals go? How do they know to go there? (Think massive groups like starlings and fish schools)
2. Simple local movement rules
3. Army Ants - 200,000 foragers. Rules are:
   1) Follow the pheromone trail (always going towards the center b/c strongest there, so they weave)
   2) Have a preferred direction (either away or to home)
   3) Turn to avoid a collision (outside = higher turning rate)

Fish Shoals - 3 behavioral zones (inside to outside)
1) Zone of repulsion - swim away
2) Zone of orientation - orient
3) Zone of attraction - swim towards

4. 1) Increase attraction and decrease orientation - swarm (all in different directions)

2) Increase orientation - torus (moving around empty core)

3) Increase orientation more - single direction movement

Question 11

What are the fountain and Trafalgar effects, and explain each? What is the Trafalgar effect named from?

Answer 11

1. Effects that occur when a predator approaches a fish school.

Fountain - maximize speed and split around predator and reassemble behind

Trafalger - tight formations quickly move in one direction to get away

2. Lord nelson’s fleet of ships in the battle of Trafalgar

Question 12

What is one way that leaders can be determined? What are two examples of this?

Answer 12

1. Voting
2. Ants (temnothorax ants) - Scout goes out to find a new colony and recruits other scouts. If they like what they see the scout just accumulates more followers until they all move.

Bees - Scouts come back and dance coding for direction of new site (intense dance = like a lot), recruit more, if they like they dance too.