Showing posts with label Social Groups. Show all posts
Showing posts with label Social Groups. Show all posts

The Home Field Advantage


          It will soon be back to the college football games in the US and the fans will be working hard to maximize their home field advantage. Animal groups too show that there is a big advantage in defending their home territory. This is often still true when a smaller group is defending their home.

This raises the question: why? It isn’t obvious why a small group should be effectively tenacious against a larger invading group, although we’re not surprised because we know it happens. Attachment to territory can be very strong, even when the loss would not be crucial to survival.

In this week’s Proceedings of the National Academy of Sciences, Crofoot and Gilby used a recording of invading Capuchin monkeys to simulate the challenge to various size capuchin groups (1).

They uncovered two interesting findings. The first was that some monkeys were reluctant fighters and would screech a lot and then make a run for it. The more monkeys in the band, the more likely a monkey was to avoid a fight. In detail they found that an increase of one more monkey to the relative group size increased the flight risk by 25%. 

The second finding was also enlightening. The monkeys on the periphery of a band were more likely to decide it wasn’t really their concern and leave than those in the middle. Everything else being equal, a capuchin in the center was 91% less likely to ease themselves out of the conflict. 

Hence, a small group doing their thing on their own patch will be very effective at defending it against a larger group drifting into their territory as a large fraction of the incomers will be at the periphery and not in the contact zone.  Hopefully most of the clashes are limited to screeching at each other with very little teeth being involved. Rather like we hope for the fans at the football games.

  1. doi: 10.1073/pnas.1115937109  (2011)


Please note that this blog is migrating to
http://jimgoodwinbooks.com/
in 6 days.

Group Dynamics – Who's In, Who's Out.


Many animals live in groups and primates are generally thought to be interesting in terms of human behavior. Not, of course, that we fit into any of the observed patterns, but behavioral scientists have fun looking for parallels.

When we look at larger groups than small family groups, we see social structures based on a dominance hierarchy. The dominant male, and it is the prerogative of the male, is at the center of the group with members spread out to the periphery. Their spatial position is a good indicator of their group status.  The normal model is that the subordinates run away after loosing a fight, or at least a peremptory challenge.

Evers et al in this week’s Public Library of Science are exercising a different model. In this case, subordinates in the group avoid more dominant members in order to avoid a dust-up (1). This well-mannered approach leads to a spread of individuals with the least dominant at the periphery and individuals getting more dominant as they get more centrally located.
This leads to a more structured group and doesn’t appear to be particular surprising. Of course, everybody won’t always be polite all of the time and some running about to avoid a thrashing will occur so that the structure is a little fluid.

Much more interesting though, is the result for really large groups. In this case the politeness leads to a well spread out population with the formation of smaller social groups among the plebs.

Not that these sub-groups are seditious and ready to start a coup, rather they are harmless local “clubs” which make their members happy. If you end up at the periphery of one of the peripheral sub-groups, it will take a degree of self-delusion to feel good about your life style. It might be time to emigrate. Easy to do in the computer model of Evers et al, but not so simple in real life.

  1. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0026189