L3. Group Living Flashcards
Why did group living evolve?
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
What are two selective pressures hypothesised to influence whether animals live in groups?
- Predator / Predation avoidance
- Resource acquisition and defence
These are not mutually exclusive pressures
What are the benefits of group living?
-Increased chance of avoiding predation
-Increased vigilance
-Dilution of risk
-Predator confusion
-Group defence
How does increased vigilance affect predators?
-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
What occurs to vigilance time as group sizes increase?
-Individuals can decrease their vigilance, with a larger group
-Open to cheating
How does a large group benefit an individual?
-The individual in the group may not need to detect a predator to be warned of the threat
-Depends on information transfer
What is the cheating hypothesis surrounding group living?
-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.
What are the direct benefits for vigilant behaviour for the individual?
-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
Explain dilution of risk.
-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
What stops dilution risk?
-If there is a linear relationship between group size and probability of detection by a predator
-Predators can attack all members of a group
What is an example of group dilution risk?
-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
What is predator confusion?
-Predators may find it difficult to single out an individual in a group to attack
-Individuals receive greater protection in more compact groups
What makes predator confusion more effective?
-When all members of the group are more alike
-Individuals that stand out may suffer more predation (the oddity effect)
What is group defence?
-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
What are other benefits to group living?
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
What is a benefit and disadvantage to finding food as a group?
-Easier and quicker to find food
-However individuals that feed in groups suffer a disadvantage through competition with other group members
How do predators benefit from group living?
-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
What disadvantages are there to group living?
-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
What is kleptoparasitism?
Food discovered by one animal is stolen by another
What are the costs and benefits to kleptoparasitism?
-Some individuals gain while others lose
-Risk of injury to both parties
-Lost opportunities to find food by conventional means
-Risk of losing prey
How can parasite burden affect group living?
-Cliff swallows nest colonially, however bigger colonies have higher numbers of swallow bugs on hatchlings (ectoparasite)
-Bugs have negative effect on nestling growth.
How does group living affect disease transimission?
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
What is a reproductive cost to group living?
-More competition between males
-Increase in aggression
-Monopolisation of females by a few males
-Cuckoldry
What is cuckoldry?
Potential cost to males that provide parental care
Females may be fertilised by males other than their mates
Describe the evolution of group living experiment with schooling guppies.
-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
What was the results of the guppy group living experiment?
-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
What did the guppy group living experiment demonstrate?
-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
What is the optimal group size?
Is when costs and benefits with group size that allows individuals to maximize fitness
-Where the net benefit is maximised
What behaviour do sparrows do when foraging?
-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
How does spatial positioning affect the benefits of being in a group?
-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
What is co-operative breeding?
-Offspring stay to help raise siblings
-Forfeit or delay chance to breed independently
What are some constraints on independent breeding?
-Shortage of suitable breeding habitats
-Reduced survival probability following dispersal
-Reduced probability of finding a mate
