BENEFITS CONFERRED BY TIMID ANTS - ACTIVE ANTI-HERBIVORE PROTECTION OF THE RAIN-FOREST TREE LEONARDOXA-AFRICANA BY THE MINUTE ANT PETALOMYRMEX PHYLAX

In this study, we demonstrate that an important benefit provided by th e small host-specific ant Petalomyrmex phylax to its host plant Leonar doxa africana is efficient protection against herbivores. We estimate that in the absence of ants, insect herbivory would reduce the leaf ar ea by about one-third. This contributes considerably to the fitness of the plant. Our estimates take into account not only direct damage, su ch as removal of leaf surface by chewing insects, but also the effects of sucking insects on leaf growth and expansion. Sucking insects are numerically predominant in this system, and the hitherto cryptic effec ts of ant protection against the growth-reducing effects of sucking in sects accounted for half of the total estimated benefit of ant protect ion. We propose that the small size of workers confers a distinct adva ntage in this system. Assuming that resource limitation implies a trad e off between size and number of ants, and given the small size of phy tophagous insects that attack Leonardoxa, we conclude that fine-graine d patrolling by a large number of small workers maximises protection o f young leaves of this plant. Since herbivores are small and must comp lete their development on the young leaves of Leonardoxa, and since a high patrolling density is required for a fine-grained search for thes e enemies, numerous small ants should provide the most effective prote ction of young leaves of Leonardoxa. We also discuss other factors tha t may have influenced worker size in this ant.