THE ECOLOGICAL FUNCTION OF EXTRAFLORAL NECTARIES - HERBIVORE DETERRENCE BY VISITING ANTS AND REPRODUCTIVE OUTPUT IN CARYOCAR BRASILIENSE (CARYOCARACEAE)

1. Shrubs of Caryocar brasiliense are intensively visited by many ant species in the cerrado vegetation of south-east Brazil. Ants collect n ectar from the extrafloral nectaries (EFNs) located on the buds at the apex of the plant. 2. The proportion of C. brasiliense shrubs occupie d by ants greatly surpassed that of neighbouring plants without EFNs a nd this resulted in many more termites being attacked and removed on t his plant than on plants lacking EFNs. Ant attacks on Caryocar were mo re frequent near the EFNs. 3. Ant-exclusion experiments with Caryocar shrubs revealed that ants significantly reduce the infestation levels by the butterfly Eunica bechina, the sucking bud Edessa rufomarginata, the bud-destroying fly Prodiplosis floricola and by a stem-galling wa sp. Ants had no effect on the infestation by a leaf-galling wasp. 4. C ontrol (ants present) and treatment (ants excluded) plants produced eq ual numbers of buds but flower and initial fruit production was signif icantly greater for ant-visited plants. Higher abortion rates of initi al fruits by control plants resulted in similar final fruit and seed s ets for plants in either experimental category. 5. The extremely low f ertility of cerrado soils is suggested as a possible factor constraini ng the ability of Caryocar shrubs to provide the resources necessary f or growth and development of their heavy fleshy fruits. Higher product ion of initial fruits by ant-visited shrubs would be neutralized by co mpetition among developing fruits and subsequent abortion. 6. Possible ant-derived benefits to C. brasiliense include: protection of vegetat ive tissues during plant growth, larger floral display and increased a ttractiveness to bat pollinators, increased male contribution to fitne ss through pollen donation and selective abortion of genetically infer ior progeny as the maternal investment is adjusted to match available resources.