Lecture 8 T Flashcards
What are the functions of animal groups?
Increased locomotor efficiency Enhanced foraging efficiency Protection from predators Swarm intelligence Coordinated movement
How do animals protect themselves?
Animals from groups under the threat of predation, being part of a group reduces the chances of predation and that larger groups confer better protection
Increasing group size leads to reduced predator attack success
How does living in a group help protect animals?
Increased vigilance within the group
Safety in numbers (the dilution effect)
The confusion effect
What is the confusion effect?
Predators have to process spatial information of multiples targets when prey aggregate, neurological constrains cause the accuracy of this processing to decline, causing the confusion effect
Many moving targets create a sensory overload of the predators sensory system and so increase the spatial error of each attack
To be effective in confusing predators, prey must be…
Fast moving
Uniform in appearance
At sufficiently high numbers
Animal choose to join groups in which members are phenotypically similar to them
What is swarm intelligence?
Social animals often have to make collective decisions, timing and direction of group travel, location of food etc
The decision making accuracy of groups is typically predicted to be grater that that of component group members
What are the benefits of swarm intelligence?
Larger groups are more effective at gathering information
Combined information is more accurate than individual information
Larger groups need a smaller proportion of informed individuals to reach a collective decision
What is coordinated movement?
Each individual is surrounded by three zones
Zone of attraction (join groups)
Zone of orientation (minimising collisions)
Blind zone
Zone of repulsion (personal space, collisions)
What are the three different rules that goven coordinated movement?
Rule 1: Each individual maintains a minimum distance from others within zone of repulsion
Rule 2: An individual will align itself with neighbours within its zone of orientation
Rule 3: An individual will be attracted towards the positions of individuals within the zone of attraction
What different types of coordinated movement are there?
Swarm
Torus
Parallel groups
What is a swarm?
A swarm occurs when individuals perform attraction and repulsion behaviours, but little or no parallel orientation
What is a torus?
In a torus individuals perpetually rotate around an empty core (milling). This occurs when the zone of orientation is relatively small and the zone of attraction is relatively large
What is a parallel group?
In a parallel group the individuals are polarised and move as a coherent unit.
Occurs as the zone of orientation becomes relatively large
What patterns emerge through group self-organisation?
Individuals follow simple behavioural rules
They rely on local information
The are unaware of what is happening to the group as a whole e.g they can evade a predator without ever seeing it
What is self-sorting
If individuals differ in the size of their zones, groups can self-sort
Individuals with smaller zones of repulsion tend to be closer to the centre and front of the group
