Mutualism

Question 1

Reciprocity is problematic because of delayed repayment

Answer 1

There is less opportunity to defect in mutualistic interactions, although each partner will seek to maximise their own fitness

Question 2

Interspecific – mutualism

Answer 2

Intraspecific – mutual benefit

- immediate shared benefits needs no special explanation e. g. improved foraging efficiency

Question 3

Mutualism in lions

Answer 3

foraging efficiency

territoriality

Question 4

Mutualism: courtship

Answer 4

Benefits to one partner may not be immediate e.g. manakins

Question 5

long-tailed manakins

McDonald & Potts 1994

Answer 5

Lek mating system

- males acquire adult plumage at 4yrs 
- males display in pairs (alpha and beta)
- alpha monopolises matings (>98%)

Reciprocity? nope
Kin selection? nope
Mutualism with delayed pay-off? Yass

Question 6

e.g. long-tailed manakins

McDonald & Potts 1994

Answer 6

Mutualism with delayed pay-offs:
females prefer cooperative display with orderly queue
alpha male gets immediate pay-off
beta always ‘inherits’ alpha status, eventually
females faithful to lek sites
beta inherits mating success too

Question 7

Many social animals post sentinels to warn of predators

Conclusion

- sentinels at low risk
- individuals act as sentinels when well fed
- sentinel behaviour is mutualistic

Answer 7

• assumed to be dangerous for sentinels
• used to be explained by reciprocity or kin selection

Bednekoff (1997):
- sentinels are safer than foragers
- explained by mutualism
…’safe, selfish sentinels’

Meerkats
(Clutton-Brock et al. 1999)
Conclusion:
Sentinel behaviour is optimal activity once stomach is full and no other animal is on guard.

Question 8

Drongos and pied babblers

Ridley & Raihani 2006

Answer 8

drongos reduce need for sentinels in small groups

babblers less responsive to drongos in large groups

babblers in large groups displace drongos

WHY?
Drongos give false alarms and take food from young babblers

foraging benefits -> kleptoparasitism

sentinel benefits -> resistance

Question 9

Mutualistic relationships are always liable to lapse into parasitism … so how is cooperation maintained?

Answer 9

Solutions

1. Facultative mutualism
2. Punishment/enforcement
3. Image-scoring/reputation

Question 10

Interspecific Mutualism: cleaners + clients

Answer 10

e. g. blue-streaked cleaner wrasse:
- eats c. 1200 parasites (isopods) per day
- inspects c. 2300 fish per day
- some clients visit cleaning stations every 5 mins

Question 11

Cleaners are tempted to cheat

- cleaners prefer fish mucus to ectoparasites

Answer 11

…why can’t they get away with this?

Question 12

Experiment
(Bshary & Grutter 2005)

Cleaners prefer prawn over flakes

Feeding on flakes (i.e. cooperation) enforced by fleeing or punishment after 6 learning trials

Answer 12

Punishment to cheaters:

Leaving/chasing the cheating cleaner

Question 13

Image-scoring / Reputation

Answer 13

Field observations (Bshary & Schaffer 2002)
Clients with a choice of cleaning stations avoid cheats
- 60% return to stations with positive last interaction
- 5% return to stations with negative last interaction

Lab experiments (Bshary & Grutter 2006)
Clients score cleaners’ cooperative image
choice of cooperative/non-cooperative
cleaners… prefer cooperative
cleaners more cooperative when being
‘image-scored’

Question 14

SUMMARY

Answer 14

1. Mutualistic interactions require no special explanation because of immediate benefit to both partners (usually)
2. Mutualisms widespread within and between species
3. Mutualists may be tempted to cheat, but costs may be reduced by facultative association, and cooperation can be maintained by punishment and need for a good reputation