Biology Reference
In-Depth Information
(a)
(c)
1.0
Transports
0.8
(b)
0.6
0.4
0.2
Tandem runs
0.0
0
20
40
60
80
Mean nest population
Fig. 6.24
Opinion polling in the ant
Temnothorax albipennis
. (a) Recruitment to
potential new nest sites occurs first by tandem running, with the follower signalling its
presence by tapping the body of the leader with its antennae. (b) After a sufficient
number of workers has voted for a new site, there is more rapid recruitment involving
transport; one worker simply carries another one to the site. Photos from Franks
et al
.
(2002). (c) In one study, the switch from tandem runs to transport occurred when there
were 20 recruits at a new site. From Pratt (2005).
Eventually a critical quorum of individuals builds up at the new site, at which there
is a switch in recruitment method from slow tandem running ('follow me') to quicker
transport, where others are simply picked up and carried to the new site (Fig. 6.24b).
In one laboratory study, where colonies nested between glass plates, the switch to
rapid transport occurred when about 20 workers had assembled at a new site
(Fig. 6.24c).
This method of slow recruitment at first is a case of 'adaptive procrastination'; it
allows the colony to inspect several potential sites before sufficient votes at one site leads
to a final decision. In theory, the optimal quorum size will reflect a trade-off between
speed and accuracy in decision making. Experiments show that the quorum size for the
switch to rapid transport to a new site is lower when conditions have deteriorated
rapidly at the old nest, so that a quicker decision to move is needed (Franks
et al
., 2003).
Honeybees,
Apis mellifera
, also set off in search for new nest sites, but their search is
on a grander scale (references in Table 6.3). A queen and some 15 000 loyal workers
wait in a swarm on the branch of a tree while scouts search up to 10 km away for a new
home. The scouts assess potential cavities and then return to the swarm and waggle
dance on the surface to advertise the new site's direction and distance (Fig. 6.25). The
vigour of the dance signals their enthusiasm for the new site. After an extended period
of signalling, in which many scouts may dance for many potential sites, a consensus is
An optimum
quorum size
Voting for a new
nest site in
honeybees: scouts
lead the way
