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| Eastern Mosquitofish creative Commons Credit : Osado |
Soon after I started out on my mile and a half trek
to get coffee, a moderately sized dog fell into step alongside. He kept his
station at two and a half feet away regardless of whether I slowed, accelerated, or weaved a little side to side. I stress it was only a little, and that it was
due to a shortage of caffeine and not a surplus of ethanol. His owner was at
the end of a long lead some way behind and he too kept station, so we were like
a mini-shoal of queer fish, albeit 2-dimensional, progressing smartly along the
sidewalk.
Animal synchronized motion as we see with flocks of
starlings or shoals of mackerel are compelling to watch as suddenly the group
seems to fold and move in a different direction. The reaction speed is amazing. The whole thing seems to be democratic with no evidence of an
alpha-mackerel leading the pack. As mackerel are rumored to have a very short
attention span, (rather like most politicians, if Republican Party debates are
any indication,) it would have to be democratic as no one would be able to
remember where they were going in the first place.
However, science is rather more interesting than politicsand
Herbert-Read et al have been studying
the shoaling behavior of a mini-shoal in a tank (1). The chosen fish were
Eastern mosquito fish which move about in small shoals eating algae and
plankton with a taste for mosquito larvae should the opportunity arise.
After a lot of photography, plotting trajectories
and speeds, the results were that the shoaling had only three simple rules.
Firstly, the fish liked to be close to their
neighbors, so that they liked other fish to be within their social space. 6 cm
is a good social distance. Secondly, they didn’t want their personal space
invaded so they accelerated away if a neighbor was tailgating. Thirdly, they
seemed to be only able to think about one neighbor at a time and so were
actually responding to their nearest neighbor interaction, so trusting that
everything else would take care of itself.
Whenever I drive on a busy freeway, I see a lot of
drivers who appear to be obeying the same three rules as they accelerate up close
and then brake and dodge to one side or another if there is a space. It seems
to be only the verges which prevent the traffic all changing direction like a
shoal of mackerel, so that if that predatory semi came rushing in from a rest
stop, the whole column would take a sharp left to avoid the large teeth on the
front of the Mack truck.
- www.pnas.org/cgi/doi/10.1073/pnas.1109355108
