Foraging rate of ants collecting honeydew or extrafloral nectar, and some possible constraints

ABSTRACT.

• 1 In a given ant species, the number of ants collecting honeydew in an aphid colony or extrafloral nectar on a plant is proportional to the productivity of the colony or plant. Thus, the number of ants per resource unit and the ingestion rate per ant are constant for a species.
• 2 Mean number of ants per resource unit and ingestion rate per ant differed considerably between the investigated species. The ingestion rate increases with the body size of the species and decreases with an increase of the mean number of ants per resource unit.
• 3 Ingestion rates were higher in ants foraging singly at the resource than in ants foraging in the normal way in a group.
• 4 It is suggested that the ingestion rate per ant is reduced below a maximum level by the number of ants present per resource unit because a certain number of ants is needed to defend the resource against alien ants. Small species need more individuals for this purpose than large species, and consequently suffer a larger reduction of their ingestion rate.