The mechanism is as follows. Bees complete patrols in random
locations that often contain no work. They then conduct
random searches for work. Hence, during periods of stable
task demand, bees diffuse away from regions of high task
demand and return after completing patrols. 

Although there is continuous movement of individuals, there is no
net movement in any direction. Now consider what happens
when task demand changes. First, bees searching for
work in regions with increasing task demand immediately
find it. There is thus an initial jump in task allocation in
such areas. 

Second, because there is continual flux of individuals
between regions, bees that finish their patrols in
zones with increasing stimulus levels simply stay there instead
of moving back to their original locations. There is
thus net movement in the direction of increasing task
demand. After a variable period of time, all of the regions
come to a new equilibrium density of bees.

Two environmental contexts lead to shifts in task allocation
in [middle age bees]. The first was explored experimentally
in this article (fig. 2) and is associated with short-term
reallocations necessitated by sharp changes in the environment.

These include temperature stress, nest damage,
and a host of other phenomena (reviewed in Winston
1987; Seeley 1995). The preceding paragraph describes
how the algorithm of this study allows bees to solve such
problems. The coupled localization/randomization mechanism
leads to an almost immediate shift of labor in any
context. 

The second type of environmental change problem
is considerably more complex and still beyond our
ability to explain. It has to do with how MABs make longterm
changes in labor allocation in response to information
received from the forager caste. 

Task allocation is a rich subject, and it is important to
consider how this work relates to previous studies (Jeanne
1986; Gordon 1996; Beshers and Fewell 2001; Sumpter
2006; O’Donnell and Bulova 2007). Two other models,
foraging for work and the response threshold model (both
reviewed in Beshers and Fewell 2001), in particular, are
relevant. 

Foraging for
work is noteworthy in that it stimulated discussion on the
important topic of spatial variability in task demand. The
model was highly abstract, however. Essentially, the model
posited that spatial variability in task demand generates
stable task-allocation patterns (temporal polyethism). 

Individuals work in one place until work runs out, at which
point they randomly search for work elsewhere. Because
the simulated nest of the model had a concentric structure
and because individuals began their lives in the center, the
model generated a temporal polyethism-like pattern of
division of labor, with young individuals working in the
center and older individuals working at the periphery.

Excerpted from:

A Self-Organizing Model for Task Allocation via Frequent Task
Quitting and Random Walks in the Honeybee

vol. 174, no. 4 the american naturalist october 2009 


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