Assessment of nectar flow rate and memory for patch quality in the ant Camponotus rufipes

SCHILMAN, P.E. & ROCES, F.

ANIMAL BEHAVIOUR

Academic Press Ltd Elsevier Science Ltd.

Lugar: London, England; Año: 2003 vol. 66 p. 687 - 693

0003-3472

Ants as central place foragers are known to repeatedly visit renewable patches such as extrafloral nectaries, yet the criteria used by workers to evaluate their quality, as well as the rules used to decide when to leave the patch, have not been identified. The present study examines both the assessment of nectar flow rate and the rules governing patch departure used by nectar-feeding ants, Camponotus rufipes. For that, single workers from a laboratory colony were trained to visit an artificial food patch providing 20% sucrose solution either ad libitum or at controlled flow rates, varying from 0.118 to 2.36 µl/min. These flow rates simulate the conditions faced by workers when visiting plant extrafloral nectaries. For the whole range of flow rates assayed, ants adjusted their visit times to the different flow rates, so that the time spent at the feeder decreased with increasing nectar flow rates. The volume of nectar collected increased with increasing nectar flow rates, and workers were observed to return to the nest with partially filled crops. To investigate the rules used by ants to decide when to depart from the patch, experienced workers, i.e. those that collected nectar at a given flow rate over four visits, were confronted in the 5th visit with a depleted patch, and the time spent there before leaving was recorded. The time spent before leaving was different depending on their previously experienced flow rate, even though ants always found a depleted patch. This suggests that ants use as a departure rule an estimate of time that depends on the flow rate previously experienced. In addition, the rate of feeding attempts at the depleted patch increased with increasing flow rates, i.e. it varied as a function of the previously experienced nectar flow rate. These results indicate that workers quantitatively assess the nectar flow rate and learn patch quality, so that they arrive at the patch with an expectation about the nectar flow rate.