Lecture 6

Question 1

Explain the evolution of group behaviour

Answer 1

. Historically, gregarious behaviour was thought to have evolved through benefits to the group/ population/ species
. Work by Williams (1966) and Hamilton (1971) changed this view that species work on behalf of the group or for a higher level
. They proposed that it was benefits to the individual that drives aggregation behaviour
(. Remember: evolution does not act on species etc.)
. Evolution acts on individuals which in turn will cause changes at higher levels such as speciation or group living etc.

Question 2

What did Williams (1966) and Hamilton (1971) suggest caused aggregation?

Answer 2

Suggested that aggregation will reduce the chance that an individual will be targeted by a predator. So they suggested the dilution effect

Question 3

If attack rate increases with group size then what does this mean for individuals?

Answer 3

That the advantage from aggregating will be lost and that the advantage only works fully if the predation rate remains constant whether in a group or alone

Question 4

What is an issue with aggregation?

Answer 4

Predators spot these very easily

Question 5

Give an example of the dilution effect being shown and who did the experimental work?

Answer 5

. Foster and Treherne (1981)
. Predator is a sardine
. Prey used were water skaters
. Skaters are not using increased vigilance (don’t really change their vigilance behaviour or anything when you put them in big groups) as fish attack from below
. Attack rate remained the same so differences in attack rate per individual are down to dilution
. Predicted values closely match observed as the number of water skaters and attacks decline linearly

Question 6

Explain the dilution effects on monarch butterflies (increased attack rate does not necessarily mean group living is not beneficial)

Answer 6

. These insects gather in vast numbers in Mexico to mate etc.
. Unpalatable but some birds will eat them
. Large groups attract more predators
. By counting remains in the roosts they found that predation rate per individual was lower
. Therefore, dilution was still having a positive effect just because there was so many of them despite the fact that they attracted more predators

Question 7

Give an example of predator swamping (the idea that synchronised emergence can ‘swamp’ predators reducing capacity to catch prey- so overwhelm predators)

Answer 7

. 2 weeks from May to June mayflies emerge, mate, lay eggs and die. They are subject to massive predation from beetles, dragonflies, birds and bats
. At the start of emergence nearly all mayfly were taken because not many
. But by the time there were 100-150 emerging per day (in a sample area) the rates of predation go right down (attack per individual is lower on the days with greatest emergence)
. Predators can’t take them in sufficient numbers
(. Also increases chance of meeting a mate)

Question 8

What has the predator swamping by mayflies also been suggested to be? What is the issue with this though? So what is it more likely to be?

Answer 8

Mating pressure but parthenogenic (species that don’t mate) mayflies show similar synchrony of emergence
More likely that predator swamping is a selective pressure

Question 9

How do aphid species use predator swamping?

Answer 9

They have this thing called a rendezvous host that they meet on in winter and they find mates and this swamp effect

Question 10

What did Hamilton (1971) suggest was the reason for aggregation?

Answer 10

That individuals will have a domain of danger. So, you will have a large one if you don’t have things either side of you if a predator comes it will be attracted to that one. So, if you form aggregation then you reduce your domain of danger. So, he suggested that aggregation formed by individuals within the group moving to minimise their domain of danger

Question 11

What is the ‘selfish herd’ effect?

Answer 11

States that individuals on the edge of groups are more at risk but also individuals that are isolated within the group should move to reduce their domain of danger. So, it is advantageous to be in the middle

Question 12

What does the selfish herd effect go some way to explain?

Answer 12

The constant movement seen in flocks, shoals, swarms etc. Because individuals are constantly moving to reduce their domain of danger because individuals will move around to gain a safer position in the aggregation

Question 13

How did De Vos and O’Riain (2010) study the selfish herd effect?

Answer 13

They studied the predation of great white sharks on fur seals. They used styrofoam to simulate fur seals and while doing that they can change the domain of danger, the distance between other individuals/ centre of the group was changed
(They detect seals as silhouettes on the surface of the water and attack at high speed from below

Question 14

What was the results of De Vos and O’Riain (2010) study on Cape fur seals in South Africa?

Answer 14

They found that the ‘fake seals’ with large domains of danger were often the ones that were attacked.
So, they found that attack rate varied depending on where the ‘seal’ was in relation to others in the group

Question 15

Hamilton predicted that an individual would seek safety in number when alarmed. How did Krause (1993) test this?

Answer 15

Tested this with dace and minnows.
. Both species studied when they are hunted exert this certain substance and other shoal members can detect this substance and they are then aware that there is a problem/ live in shoals and these shoals tighten when chemicals from damaged skin are present

Question 16

What were the outcomes/ results of Krause (1993) experiment on Hamilton’s prediction that an individual would seek safety in numbers when alarmed? (The experiment done with dace and minnows exerting substances)

Answer 16

. Dace were habituated to the chemical and Minnows were then introduced. Found that before that substance was introduced they behaved like dace but when you introduced these chemicals to the dace shoals where this alarm substance was being released they positioned themselves so they were surrounded/ made sure there were a bunch of individuals around them which they didn’t do before
. Minnows positioned themselves so that they were surrounded by dace when exposed to the chemical

Question 17

What influences where you want to be in a shoal?

Answer 17

Depends not just on predators but if you are hungry. Hungry fish often go in front where they will find food.
Hungry fish occupy frontal positions, satiated fish will be more central

Question 18

What is the confusion effect?

Answer 18

. Individuals within an aggregation can be difficult to target effectively
. It has a very hard to focus on one individual when may others are moving within line of sight

Question 19

How did Neil and Cullen (1974) test the confusion effect? What were the outcomes/ results? What have some other experiments like this shown about predators, give example?

Answer 19

. They looked at 4 predators: cuttlefish, squid, pike and perch attacking small fish prey
. All 4 predators success rate declined with increasing group size (confusion effect)
. Most apparent in the perch which chases its prey (the rest are ambush predators)
. Perch had to continually change targets
. Some experiments like this have shown that some fish prefer individuals on the outside of the shoal such as sticklebacks attacking Daphnia

Question 20

Give an example of an experiment carried out to study the ‘oddity effect’ (how did they do it and what did they find)

Answer 20

They painted just one or two individuals in the shoal blue, so the energetic value of them doesn’t change just the visual appearance of them and they found that predators preferentially went for the odd one (it is probably related to the salience model because they are easier to follow)

Question 21

Explain the oddity effect

Answer 21

. Studies have shown that predators prefer to attack odd coloured individuals
. It is believed that this will help predators to counteract, to some degree, the confusion effect
. Comes back to saliency: high saliency individuals will be more easily noticed by predators
. This can be good (aposematism) or bad (albino animals rarely survive long in nature)

Question 22

Communal defence: many animals are not passive when it comes to predator attacks. Give the black-headed gull example of communal defence against attacks

Answer 22

. Black-headed gulls will attack crows that come too close to their nesting colonies looking for eggs and chicks
. More central nests have more defending gulls and therefore crow success is lower further into the colony
. So, the denser the colony is in the middle the more heads you have to defend and the higher success you have against predators

Question 23

Give the communal defence example guillemots

Answer 23

Densely packed nests mean that there are many birds available to attack any predators such as gulls

Question 24

How did Andersson and Wicklund study communal defence? What did they find?

Answer 24

. They used fieldfares and put artificial nests near and away from the colonies and they found that the ones near the colonies suffered less predation
. Nests in colonies in Scandinavian woodland
. Will mob predators and defecate on them
. Study showed that artificial nests placed near the colonies suffered lower predation than artificial nests placed near solitary fieldfare nests

Question 25

Why is vigilance in prey species important?

Answer 25

Because many predators rely on surprise, ambushing prey from cover. If an individual spots a predator early then it has a greater chance of escape

Question 26

What did Kenward (1978) find when studying goshawks and wood pigeons group vigilance?

Answer 26

. Goshawks have reduced success when hunting wood pigeon in larger flocks
. Larger flocks take flight when the predator is further away
. What is probably happening here is that one individual spots the predator early and starts escape which alarms the whole flock (Pulliam, 1973)

Question 27

Explain Bertram (1980) study of ostrich group living (what did he find, how was it positive)

Answer 27

. He found that an individual ostrich spent less time scanning for predators when in a group than when alone
. When alone the individual spends quite a lot of time being vigilant but when in a group the percentage of time goes down because there is a good chance that there is another individual being vigilant
. The overall vigilance of the groups was greater than a single individual
. Also, birds would raise their heads randomly, so no pattern was present which prevents lions exploiting the behaviour

Question 28

What are the positives of group living reducing vigilance of an individual?

Answer 28

. Less time being vigilant per individual gives more time to feed
. Many eyes provide better warning when predators are close
. Dilution also reduces predation risk in a group and therefore may also reduce vigilance of the individual (so if your area of danger is being reduced then that is another reason why you can spend less time being vigilant)

Question 29

What are the negatives of group living reducing vigilance?

Answer 29

As group size increases feeding competition may increase so reduced vigilance and greater feeding time may actually be a cost rather than a benefit

Question 30

How did Magurran and Higham (1988) study response to alarm behaviour in minnows when threatened by a model pike?

Answer 30

. Had two groups
. Some minnows could see the pike through a one-way mirror (transmitters)
. Others could only see the other group of minnows (receivers) (so the second group couldn’t see the pike)
. When observing alarm behaviour in the transmitters the receivers hid despite having not seen the threat
. So being in a group can allow you to receive the alarm signals of other individuals in the group

Question 31

Describe how responding to alarm calls was demonstrated in water skaters

Answer 31

. They respond to conspecific (means same species) alarm behaviour
. Demonstrated that when approached by a model predator, anti-predator movement spread throughout the flotilla of water skaters as they bumped into each other
. ‘Trafalger effect’
. So, the predator may be quite some distance away so that they can’t detect it at all but it passes through the group

Question 32

Using ostriches as an example how can individuals cheat in group living vigilance?

Answer 32

. Can cheat in a group and spend more time feeding and less time vigilant and that is a group of 20, 30 individuals then that doesn’t make that much difference to overall group performance of vigilance
. Additionally, it will benefit from the increased overall vigilance of the whole group
. But if they all cheat then vigilance will suffer, and predation will increase to the point where the benefit of group vigilance is lost

Question 33

What is the ESS when talking about vigilance?

Answer 33

The amount of vigilance that an individual should show within a group, should go down as group size increases and when you get to a large group size then the benefits don’t change much

Question 34

What are the negatives of cheating in a group? With examples

Answer 34

. More likely to get targeted by predators: Cheetah in the Serengeti chose less vigilant Thomson’s gazelles in 14 out of 16 attacks
. Additionally, the gazelles that were caught were less vigilant during the stalk and did not spot the predator as early as those that were more vigilant
. In birds individuals that are vigilant spot alarm flights of others sooner and react more quickly than less vigilant birds

Question 35

How was the fact that individuals that are vigilant spot alarm flights of others sooner and react more quickly than less vigilant birds been experimented?

Answer 35

. Lima (1994) demonstrated this experimentally by rolling a ball at a bird on a feeder
. Only the target bird could see the ball
. Target responded first, then vigilant individuals followed by the less vigilant

Question 36

Why do species that feed on ephemeral patches of food such as seeds or fruit tend to live in groups?

Answer 36

. Limiting stage of feeding is usually finding patches
. Patches tend to be rich in food while they last
. Was suggested that these colonies work like ‘information centres’
. Individuals can follow other more successful foragers to good feeding sites

Question 37

What do individuals gain by telling anonymous individuals/ sharing information about where food is?

Answer 37

. It could be as simple as benefits from group living such as dilution or increased vigilance
(. If this is true then the term recruitment centre is better)
. If this is turned around and the reason for grouping is predation pressure then individuals in the group could simply follow successful foragers without them signalling
. More like eavesdropping than passing information in this case

Question 38

What is the information sharing theory?

Answer 38

Theoretical studies have shown that sharing information can drive the evolution of communal roosts

Question 39

What must be true for the information theory to be true?

Answer 39

1) pooling of many individuals search effort increased chance of finding food resource
2) little cost of foraging in a group due to size or richness of patch

Question 40

Under the two conditions for the information sharing theory to be true then what can be an ESS?

Answer 40

‘Search independent and recruit others’ can be an ESS.

So, birds could go out and find something and then recruit others

Question 41

What is the evidence for information sharing at roosts?

Answer 41

. Ravens were studied
. Found that territorial pairs could fight off a small number of juveniles from a carcass
. Once the number of juveniles reached 6 however they would give way
. Juveniles discovering a large defender carcass will call loudly to recruit others
. Most effective recruitment was at roosts

Question 42

How was information sharing in roosts studied?

Answer 42

. Study of raven roosts
. Sheep and hare carcasses places 2-30km from roosts
. Carcasses were embedded with coloured plastic beads
. Pellets (each one had a different colour of pellet in) were ingested by the birds then, when back at the roosts, they were regurgitated in pellets
. Beads from particular carcasses appeared at specific sites within the roost suggesting that birds that fed together also slept together
. Radius of beads free daily indicating that information about the carcass was being transmitted with more birds joining the group
. The groups left the roost together, led by the birds in the centre and they flee directly to the carcass

Question 43

What did the results of the information sharing at roosts studied using raven roosts indicate?

Answer 43

Indicates that individuals are sharing where food sources are with each other. Another idea is that it is parasitising information, that uninformed individuals are parasitising the knowledge of the informed individuals