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