Biology Reference
In-Depth Information
Organism
Decision
Behaviour
References
Table 6.3
Examples of
opinion polling
and consensus
decision making
in groups
(Conradt & Roper,
2005).
Honey bee
Apis
mellifera
Choice of new nest
nest site
Scouts waggle dance
to recruit
Visscher &
Camazine (1999)
Seeley & Buhrman
(2001)
Seeley (2003)
Ant
Temnothorax
(formerly
Leptothorax
)
albipennis
Choice of new nest
site
Workers recruit by
tandem runs and then
transport
Franks
et al
. (2002)
Pratt
et al
. (2002)
Pratt (2005)
Whooper swan
Cygnus cygnus
When to move
after a rest
Head movements
Black (1988)
Mountain gorilla
Gorilla gorilla
beringei
When to move
after a rest
Calls ('grunts')
signalling impending
departure
Stewart & Harcourt
(1994)
African buffalo
Syncercus caffer
Which direction to
move after a rest
Stand up and gaze in a
particular direction.
Prins (1996)
Animal groups also sometimes make decisions based on how individuals vote
(Table 6.3). Herbert Prins (1996) studied African buffalo in Manyara, Tanzania.
Females and their offspring lived in large, stable herds of several hundred individuals.
During the heat of the day the herd usually lay down to rest, and then towards dusk
they all went off as a group to feed in one place. How does the herd decide where to go?
Before the herd sets off, individuals occasionally stand up and then lie down again. At
first sight, this seems to be individuals simply stretching their legs. However, Prins
noticed that individuals adopted a special posture when they stood up; they gazed
steadily in one direction and held their head up high. He took note of the directions of
gaze and discovered that the herd's eventual direction of movement could be predicted
by the vector of the individuals' gaze directions. He suggested that individuals were
voting and that the group moved off once there was a consensus about where to go.
The best evidence for voting comes from studies of how social insect colonies choose
a new nest site (Franks
et al
., 2002; Table 6.3). The ant
Temnothorax
(formerly
Leptothorax
)
albipennis
lives in small colonies (less than 500 workers) that nest in rock
crevices. When a crevice crumbles, the colony has to find a new nest site. These ants are
tiny (workers are 2.5 mm long) and the area they search is just a few square metres.
When a scout finds a potential new site, it returns to the colony and begins to lead other
ants to the site, one by one, by tandem running. This involves walking ahead of the
follower, who signals its continued presence by tapping the leader's body with its
antennae from time to time (Fig. 6.24a). If the recruit approves of the new site it, in
turn, will lead further recruits to the site.
During this search phase, several sites may be inspected and recruits may build up
and then decline at various sites depending on how individuals assess their suitability.
Buffalo herds:
voting when and
where to go
Ants: voting for a
new nest site
