Collective Behaviour
Dr Andrew Jackson
Zoology
School of Natural Sciences
Trinity Centre for Biodiversity Research
Trinity College Dublin
Examples from Cells to Beasts
Advantageous Information Transfer
Collective Behaviour
• http://vimeo.com/31158841
Complex Social Environment
How do we get
from simple
individuals….
… to complex
groups?
The basic rules
1. Personal space - cant occupy the same space
as someone else
2. Imitation - tend to copy others and will
seemingly follow another without prompting
3. Gregarious – they don’t like being on their
own, so will move towards others if isolated
Individual Based Model (IBM)
Repulsion
Orientation
Attraction
Blind Spot
Local Interactions
Collective behaviour
• Emerges as a result of interactions between
individual “agents”.
• Properties of the group are not encoded
directly by behaviours at the individual level.
• Patterns emerge through self-organisation of
the system
Matlab example
Sensitivity to individual behaviours
• Vary only the zone
of orientation
Blind Spot
Swarming
Small zone of
orientation
Matlab Swarms
Torus (ring-doughnut) patterns
Intermediate
zone of
orientation
Matlab Torus
College Park Torus
Directed Shoal
Large zone of
orientation
Matlab Directed Shoals
Individuals are different
Variation in behaviour
Matlab example (swim speed)
Fast-slow video
Finding your way around your group
Fast
High
Rate of
Turning
Larger
zone of
repulsion
Subtle behavioural changes
• Gives evolution an easy (well easier) way to
effect dramatic change at the group level
pattern
– Key concept in developmental biology
• Don’t need complex cognitive processing and
rules to navigate and negotiate the group
complex
But clearly some individuals do
have information…
Collective Decision Making
Coercion is easy
… but depends on numbers
Few informed individuals
• Crowd video – few informed individuals
Many informed individuals
• Crowd video – many informed individuals
Conflict of information
• Crowd video – conflict of information
Few individuals can sway a group
• Only a small proportion
of informed individuals
needed to influence the
crowd
• Larger groups need
smaller proportion of
informed individuals
reach a collective
decision
Conclusions
• Complex collective behaviour derived from
local interactions between individuals.
• Group level properties emerge – the whole is
greater than the sum of its parts.
• Need to take a holistic approach to these
systems.
Suggested Reading
•
•
•
•
•
•
Dyer, J. R. G., Johansson, A., Helbing, D., Couzin, I. D., & Krause, J. (2009).
Leadership, consensus decision making and collective behaviour in
humans. Philosophical Transactions of the Royal Society B: Biological Sciences,
364(1518), 781-789. [pdf]
Couzin, I. D. (2007). Collective minds. Nature, 445(7129), 715-715. [pdf]
Couzin, I. D. (2006). Behavioral Ecology: Social Organization in Fission-Fusion
Societies. Current Biology, 16(5), r169-r171. [pdf]
Couzin et al. 2002. Collective memory and spatial sorting in animal groups. J Theor
Biol. 218, 1-11. doi
I suggest you watch this short 5 minute video about collective behaviour by Prof
Iain Couzin http://youtu.be/_2WqH_HUxz8 , and basically anything Iain publishes
is pretty cool by me http://icouzin.princeton.edu/
And the starlings are always worth viewing - http://vimeo.com/31158841