Groups Flashcards
What are the advantages of grouping?
Protection against predators
Improved foraging for food
Why do animals aggregate?
Due to attraction to a specific environmental factor e.g. food
How do groups provide protection against predators?
- Improved Vigilance
- Dilution
- Shielding
- Predator confusion
- Group defensive behaviour
How do animals benefit from the vigilance of others?
They spend more time feeding and less time watching out
The more scanners there are the quicker the response to a predator
An example of predators being less successful due to group vigilance
Goshawks are less successful attacking larger flocks of pigeons
The pigeons fly off earlier while hawk is still distant
Why do individuals not cheat?
The first animal to spot the predator has the best chance of escape
What is dilution?
The larger the group the less likely it is for an individual to be taken by a predator
Examples of dilution
Horses in larger groups are bitten less as seen in the Camargue cluster when tabanid flies are active.
Shielding
Members of a group use other members as protection - a living shield - against predators.
What is the result of shielding?
There will be a clumping of individuals, where the individuals might be safer if they agreed to spread out
What does the fitness payoff of an individual in selfish herding depend on?
It depends on what others in the group are doing
An example of the prediction of the selfish herd hypothesis
In Bluegill sunfish
- the central nesting sites are the safest
- the males compete intensely
- the central territories are won by larger fish
Predator confusion
Many prey moving about make it hard for the predator to fix on and follow any one of them.
How is predator confusion shown in fish?
- A pike given one prey fish at a time in a tank catches more prey per unit time than when feeding on shoals of fish
- Minnows marked with ink were more likely to be eaten in a group of minnows without the mark
-the markings make it easier for the predator to keep an eye on them
An example of how predator confusion explains alarm calls
Ground squirrels give the alarm call, then all run to safety confusing the predator
The caller has a 10-fold lower risk of being eaten than other squirrels
How does Kruuk’s experiment support the hypothesis for the adaptive value of mobbing behaviour?
Mobbing behaviour distracts predators from the mobbers’ offspring
- Hen eggs were placed inside (protected by mobbing) and outside a gull colony
- The predators (crows) were mobbed more
- the crows were less successful in their predation attempts when targeting eggs within the colony
Example of interspecific altruism
Humpback whales save other species from orca attack
- appear to protect seal by keeping it on its belly
How is group defence shown in mammals?
Buffalo’s travel with their young near the centre of the herd
How do honeybees communicate about the location of food?
The scouts perform a waggle dance
What are information centres?
Individuals find out about the location of good feeding sites by following others
- proposed by Ward and Zahavi
What are the predictions of the information centre hypothesis?
- Birds should leave in groups and fly off in the same direction e.g., barn swallows
- Leaders of groups should be birds that were recently successful e.g., shown in cliff-nesting swallow and Osprey
Flocking is advantageous to which species?
species that exploit food that is patchily distributed and unpredictable (e.g., seeds)
What type of defence is important in predators such as lions and hyenas?
Cooperative carcass defence may be more important than cooperative hunting in predators such as lions and hyenas
An example of how animals protect themselves from physical factors.
-Emperor penguins huddle together for warmth
-Colonial weaver birds’ nests maintain uniform temperature
What are the disadvantages of grouping?
- Increased conspicuousness to predators
- Competition in feeding
An example of increased conspicuousness
A colony of fieldfare nests attract more predators than a single nest
- But nests also protect them from mobbing
What are the two types of competition in feeding?
- Direct exploitation (many mouths compete for food)
- Interference
Example of direct competition for food
Predator fish (Jack- Coho salmon) do better in a group but those at the front catch more prey than those at the back
An example of interference between group members
Redshank feed on shrimps that retreat into burrows when they detect an approaching bird
What is nearest- neighbour distance?
It reflects a balance between the costs (interference) and the benefits (protection) of group living
- e.g. in knots distance is higher during the day (feed on shrimp) than at night (feed on snails)
How does increased parasite transmission occur in cliff swallows?
They build nests close together and favour swallow bug transmission
Cuckoldry and mate competition occurs in which birds?
In colonial-nesting red-winged blackbirds the mates of vasectomied males laid fertilised eggs by a male other than their mate
An example of a group where cannibalism of the young occurs?
In bluegill sunfish a male may eat his neighbour’s eggs
- reduces benefit of group defence against predators
An example of a group where cannibalism of the young occurs?
In bluegill sunfish a male may eat this neighbour’s eggs
- reduces benefit of group defence against predators
What is the optimal group size for an individual?
It is the size at which
- fitness is maxismised
- time spent in vigilance and fighting combined is lowest
What are the effects of group size on Yellow eyed Juncos?
As group size increases
- birds spent less time in vigilance
- spent more time fighting
Optimal group size depends on what environmental factors?
-predator risk
-food availability
-cover availability
Group size may vary depending on what activities in rooks.
-feeding
-nesting
-winter roosts
