HERBIVORY AND THE LONG-LIVED LEAVES OF AN AMAZONIAN ANT-TREE

1 Tachigali myrmecophila (Caesalpinaceae) is an Amazonian myrmecophyti c canopy tree. The saplings are shade-tolerant, surviving in a suppres sed state for several years in the rainforest understorey, the hollow leaf rachis and petiole being inhabited by the stinging ant Pseudomyrm ex concolor (Pseudomyrmecinae). An experiment was designed (a) to eval uate the role of insect herbivory in the mutualism between T. myrmecop hila and P. concolor and (b) to test a falsifiable hypothesis proposed by a current trade-off model of chemical and ant defences which predi cts that myrmecophytic traits should be limited to plants with leaves of low longevity. 2 Plants from which the ants were experimentally rem oved had 4.3 times more herbivorous insects than plants with ants. All recorded orders of insects were attacked similarly by the ants. Rates of herbivory were: (a) ten times higher on experimental plants lackin g ants, (b) about three times higher on immature than mature leaves, ( c) about two and a half times higher in the wet than the dry season. A fter 18 months, the experimental plants presented an accumulated level of leaf herbivory which was about twice as high as for the plants wit h ants. 3 Observations on the phenology of control, experimental, and naturally unoccupied plants revealed that the leaf longevity of plants with active ant colonies was unexpectedly high for rainforest (81 mon ths), and about 1.8 and 2.6 times as high as the experimental (45 mont hs) and the naturally unoccupied (31 months) plants, respectively. The high leaf longevity of the myrmecophytic T. myrmecophila does not sup port the current trade-off model of chemical and ant defences. The rat e of apical growth was 1.6 times higher for plants with ants than plan ts from the experimental group. The slow growth rate of T. myrmecophil a, about 14 cm year(-1), is compatible with the resource availability hypothesis. 4 Phenological differences between experimental and natura lly unoccupied plants suggest that descriptive-correlative studies wou ld not always give a true picture and that the actual paradigm of ant- plant interactions, derived in part from this approach, should be care fully revised. 5 The results corroborate the hypothesis that the inter action between Tachigali myrmecophila and Pseudomyrmex concolor is mut ualistic, and suggest that attack by phytophagous insects is the prime factor in the evolution of the myrmecophytism.