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)

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