Biomedical Engineering Reference
In-Depth Information
their surroundings, but it is a challenge to sense the
surroundings using cameras to accurately detect
other vehicles. The very low weights of these vehi-
cles also set severe limitations to the on-board com-
puter handling.
13.3 COLLECTIVE DECISION
MAKING
A person with limited biological knowledge
could think that decisions in large insect societies
follow the classical hierarchical structure known
from pre-democratic human cultures and the
business world, where a leader individual orga-
nizes and controls the behavior of the follower
individuals. Thus larger strategic decisions such
as how to allocate tasks to individual workers,
foraging priorities, and new nest selection would
be under the direct control of the ant or bee queen
via pheromones. However, this is not the case.
Such decisions are reached by the collective
actions of individuals following simple behavio-
ral rules. Decisions on choosing an optimal path
to a food source in ants is, for instance, primarily
determined by the chemical concentration of
recruitment pheromones left by other foraging
workers
[2]
. The simple behavioral rule of fol-
lowing the path with the highest pheromone
concentrations can explain the correct choice
between a shorter path and a longer path lead-
ing to the same food. If we imagine two foragers
that continuously deposit pheromones as they
follow the paths, with one ant collecting food by
taking the short path and the other ant taking
the longer path, then the ant following the
shorter path will take shorter time and thus pass
by a given point on the path more often than the
ant on the longer path. Since the foragers con-
tinuously leave a pheromone trail as they move,
the concentration of pheromone on the shorter
path will automatically become higher as time
passes (
Figure 13.3
). New foragers will therefore
choose the shorter path, which will then get an
even higher pheromone concentration.
FIGURE 13.3
The basic principle used by ants to find
the shortest route to a food source. Ants leave odorant tracks
(pheromones) that quickly evaporate. The more often the
track is passed, the stronger the odorant is and is therefore
preferred by ants that follow.
However, in this section we focus on another
well-studied behavior: swarming and nest-site
selection in honeybees. Honeybees live in large
colonies with one queen and up to 100,000 work-
ers. In the spring, the queen begins to lay eggs
destined to become new queens. Soon after these
new queens emerge, the old queen, along with a
sizable number of the workers, forms a swarm
and leaves the old nest. The swarm usually set-
tles on a tree for a couple of days while scouts
are sent out to search for new nest sites. Nest-site
selection and swarm lift-off are determined by at
least four different communication methods, as
illustrated in
Figure 13.4
[16]
: (1) In the waggle
dance, scouts advertise the position of possible
nest sites to other scouts. (2) Vibration signals,
which consist of scout bees vibrating their bodies
rapidly, are used to stimulate other bees and
