Evolutionary models ofcollective behaviour inanimal groups	  Vishwesha Guttal
Centre for Ecological Sciences
Indian Institute of Science, Bengaluru, IndiaInterna(onal	  Conference	  on	  Mathema(cal	  Modeling	  and	  Applica(ons	  	  	  Meiji	  University,	  26th	  Nov	  2013	  Image credit: Ingo Arndt

Collaborators!

Iain Couzin, Princeton University!

Christos Ioannou, Bristol!

Pawel Romanczuk, Max Planck Institute for Complex Systems!

Stephen Simpson, The Univ. of Sydney!

Gregory Sword, TAMU!

Debasish Chowdhury, IIT Kanpur!

Jaideep Joshi, IISc, Bangalore!

Many others!

Broad relevance of collective behavior	  	  	  	  !

Various	  disciplines:	  	  !

Physics;	  Robo(cs;	  Computer	  Scien(sts;	  	  !

Traﬃc	  organiza(on;	  Human	  crowds;	  etc.	  Physicists’s approach: Individuals (micro) to collectives (macro)
How do individual level interactions scale to collective patterns
Individual	  level	  interac(ons	  •Self-­‐ordered	  collec(ve	  mo(on	  System of self-driven interacting particles–

Agent/CA based models: follow average direction of particles in their neighborhood with some error/noise (Vicsek, et al, 1995,
PRL; Chowdhury et al, Phys Rep, etc).

–

Biologically more realistic interactions: Repulsion, attraction, alignment, information about environment (Chate et al,Couzin et al, Parrish, et al).

–Continuum hydrodynamic description: universal macroscopic features (Ramaswamy, Toner, Tu, etc).

Image	  Credit:	  hQp://richardschwartz.ﬁles.wordpress.com/2010/07/ﬁsh-­‐school.jpg	  Why do organisms show collective movement?

Living in groups!

Why do animals live in groups?

!

Tempting to say:!
!

!

They benefit as a group.
Their chances of survival increases as a group.

In evolution, all that matters is relative individual
fitness but not whether the individuals/groups areoptimal.

Run fastest,tiger will
eat us!!!

No, I justneed to run
faster thanyou!

Image credit:(Running) http://2.bp.blogspot.com/-Lwokg-XmBa0/TjRL-OmPn0I/AAAAAAAAAUg/F8esVnphX5Y/s1600/running%2Bcartoon.jpg(Tiger) http://www.clker.com/cliparts/b/9/7/8/1209672469905052952Telemachos_tiger_4x_b_w_2.svg.hi.png

Evolution of collective behaviour
Migration and evolutionary
branching of leaders and social followers!

Guttal & Couzin, 2010, PNAS!

Guttal & Couzin, 2011, Comm IntegrativeBiol.

Predation and coordinated collectivemovement!

Ioannou, Guttal and Couzin, 2012,
ScienceCannibalism and collective migration ininsects
Guttal et al, 2012, Ecology Letters!

Altruism and collective movement!

Joshi and Guttal, In prep.

A fusion of simulations and realanimals!

Fact:	  Bluegill	  sunﬁsh	  responds	  to,	  and	  tries	  to	  aQack,	  moving	  dots	  on	  side	  of	  a	  tank.	  	  Prey	  simula(ons	  Image	  courtesy:	  Christos	  Ioannou	  and	  hQp://bplteensofwa.ﬁles.wordpress.com/2009/07/computer.jpg	  Simulated	  prey	  !

Traits!
!
!

!

ωip : Persistence (lack of sociality)ωia : Attraction
ωio : Orientation/Alignment

Motion!

di(t+Δt) = ωip *di(t) + ωia *dia(t)+ ωio *dio(t)!

Plus randomness in motion.

Simulated	  prey	  !

A	  heterogeneous	  popula(on	  (size	  16)	  	  Having	  varying	  degrees	  of	  	  social	  interac(ons	  !
!
!
!

En(rely	  solitary	  (random	  walk)	  Strongly	  align	  with	  neighbors	  Strongly	  aQract	  towards	  neighbors	  And	  a	  balance	  of	  the	  above	  1	  0.8	  Alignment:	  wio	  	  !

0.6	  0.4	  0.2	  0	  -­‐0.2	  0	  0.2	  0.4	  0.6	  0.8	  1	  -­‐0.2	  A+rac/on:	  wia	  C C Ioannou, V Guttal and I D Couzin, Science, 20121.2	  Let	  the	  Bluegills	  aQack	  digital	  prey	  Analyze	  the	  data	  !

Iden(fy	  the	  trait	  of	  the	  individual	  who	  got	  aQacked	  (aQrac(on	  and	  alignment	  coeﬃcients).	  	  1	  Based	  on	  70	  trials:	  size	  of	  circle	  is	  frequency	  of	  aQacks.	  

0.8	  0.6	  Alignment	  !

0.4	  0.2	  0	  -­‐0.2	  0	  -­‐0.2	  0.2	  0.4	  0.6	  0.8	  1	  A+rac/on	  C C Ioannou, V Guttal and I D Couzin, Science, 20121.2	  What	  causes	  large	  scale	  locust	  swarms?	  
!

A very local phenomenon:!

Density-dependent phase-change in locusts!

Solitary @ low densities!

!

!

Locusts are shy, solitary insects

Gregarious @ at high densities!

Switch to gregarious behavior!

Are attracted towards other individuals

Locusts	  are	  cannibalis/cSimpson et al, Biol. Rev., (1999);
Bouaichi and Simpson, Phys. Ent. (2003).;
Bazazi, et al, Current Biology (2008)

Why	  do	  locusts	  show	  phase-­‐change	  and	  collec/ve	  movement?

!

Hypothesis: Density-dependent phase-change in locusts reducesrisks of cannibalism in locusts.

Local	  interac(ons	  (response	  to	  neighbors	  movement)	  !	  	  	  	  	  Response	  to	  individuals	  approaching 	  	  Response to those moving away fromyouIndividual traits are determined by natural
selection!

Recall	  that	  traits	  are:	  !
!

Response	  to	  those	  moving	  away	  (ωm)	  Response	  to	  those	  approaching	  (ωa)	  !

We	  do	  not	  predetermine	  what	  the	  individual	  traits	  in	  the	  popula(on	  are.	  	  

!

They	  are	  going	  to	  be	  determined	  by	  “natural	  selec(on”.	  	  	  Cost	  of	  cannibalism	  alone	  explain	  the	  phase	  change	  behavior	  in	  Locusts!	  	  	  	  	  	  i.e.,	  the	  phase	  change	  strategy	  minimizes	  the	  risk	  of	  being	  cannibalized	  for	  individuals.	  	  	  	  Gu(al	  et	  al,	  2012,	  Ecology	  Le7ers	  Acknowledgements
oCollaborators:!

Iain Couzin, Princeton Univ; Christos Ioannou, Bristol Univ. UK!

Pawel Romanczuk, Max Planck, Germany!

Stephen Simpson, The Univ. of Sydney
Gregory Sword, TAMU!

!

Funding:
DBT, MoEF, IISc (India); DARPA, NSF (USA);!

Thanks to all of you!