Groups Flashcards
(38 cards)
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
