Neotropical ant-gardens: Behavioral and chemical ecology of an obligate ant-plant mutualism.

Seed dispersal mutualisms are essential for the survival of diverse plant species and communities worldwide. An outstanding but poorly understood ant-seed mutualism occurs in the Amazonian rainforest, where arboreal ants collect seeds of several taxonomically diverse plant species and cultivate them in nutrient-rich nests, forming abundant hanging gardens known as ant-gardens (AGs). AG ants and plants are dominant members of lowland Amazonian ecosystems, and their interaction is obligate and apparently species-specific. Though established AGs are limited to specific participants, it is unknown at what stage specificity arises. Seed fate pathways in AG epiphytes are undocumented, and the recognition cues that mediate the mutualism are unknown. Here the species specificity of the AG ant-seed interaction is assessed, and chemical cues are characterized that elicit seed-finding and seed-carrying in AG ants.;To examine the specificity of the ant-seed interaction, general food baits and seeds of the AG plant Peperomia macrostachya were offered on alternate days at 108 bait stations. Seventy ant species were detected at food baits and could have interacted with AG seeds, but only three species collected P. macrostachya seeds, and 84% of observed seed removal by ants was attributed to C. femoratus. In a separate experiment, arthropod exclusion significantly reduced AG seed removal rates, but vertebrate exclusion did not. Thus species specific seed dispersal, rather than post-dispersal processes, appears to be the primary determinant of the distribution of AG plants. The results also begin to quantify factors that affect seed fate in this unusually specific plant-animal mutualism.;To characterize behavioral cues on AG seeds, solvent extracts of three species (Anthurium gracile, Codonanthe uleana, and P. macrostachya) were subjected to chromatographic fractionation. To test behavioral activity, each fraction was applied to other seeds that ants ordinarily ignore. At least