1. Division of Labor and Task Allocation
Robert Herbig
Peter Fine

2. Overview Division of Labor Response Thresholds Models One Task
Several Tasks
“Emergent” Task Succession
Model 1
Model 2

3. Division of Labor Simultaneous task performance by specialized workers
Better than sequential task performance by unspecialized workers
Examples:
Reproduction
Foraging
Hive defense
Cleaning of the nest

4. Division of Labor Temporal polyethism (Age castes)
Individuals of the same age tend to perform identical tasks
Worker polymorphism (Morphological or physical castes)
Workers have different morphologies
Individual variability (Behavioral castes)
Differences among individuals in the frequency and sequence of task performance

5. Division of Labor Specialization Plasticity Resilience
Division of labor is rarely rigid
Ratio of workers performing different tasks varies in response to changes
Resilience
How much the colony responds to alterations
Determined by elasticity at the individual level

6. Response Thresholds
Individuals perform a task when their threshold is met
When a task is performed, the threshold for that worker for that task is lowered
Honey Bee

7. Response Thresholds Pheidole pallidula ant species:
Major workers have higher thresholds for foraging and nest defense than minors

8. Response Thresholds Ectatomma ruidum ant species:
Specialized “stinger ants” retrieve prey if necessary

10. Models with One Task
Inactive individual performs tasks with probability P:
P(Xi=0 -> Xi=1)=Tθi(s)=s²/(s²+ θi²)
Active individual gives up task and becomes inactive with probability p:
P(Xi=1 -> Xi=0)= p
Average time spent on a task: 1/p
Stimulus intensity:
s(t+1)=s(t)+δ-αNact/N

11. Models with Several Tasks
Given m tasks with Nij the # of workers of type i engaged in task j
Two equations govern this complex model:

12. Models with “Emergent” Task Succession
Individuals have identical response thresholds
Thresholds vary for each task
Success rate varies for each task
In general, heavy items are “carried” (processed) after lighter items
Examples:
Brood sorting of Leptothorax ants
Carrying leaf fragments to their appropriate location

13. Models with “Emergent” Task Succession
Performing a task increases the demand for another task
One task will generally be followed by another
Examples:
Creating a pile of refuse at the entrance to the nest generates a need for cleaning
Killer ants kill prey, which increases the need for transportation of the corpses

14. Questions? ?