TREE-EPIPHYTE-ANT RELATIONSHIPS IN THE LOW INUNDATED FOREST OF SIAN-KAAN-BIOSPHERE-RESERVE, QUINTANA-ROO, MEXICO

Research on epiphyte (9 bromeliads and 1 orchid) relationships with host trees, and with arthropods, especially ants, was undertaken in the low inundated forest of Quintana Roo, Mexico. Epiphyte association with host trees is determined by the interaction of the epiphyte seed type and dispersal mode with the bark type of the host. Airborne seeds of the Tillandsia spp, are caught on the rough-barked and small, spiny branches of Bucida spinosa; flat, ovoid seeds of Aechmea bracteata, which are disseminated by birds, germinate principally on Haematoxylum campechianum and Erythroxylum confusum, two rough-barked tree species, often in forks of major branches, and never on B. spinosa; the minute seeds of Schomhurgkia tibicinis germinate generally on E. confusum, but also on Manilkara zaposa and rarely on B. spinosa. Epiphyte association with non-ant arthropods is determined principally by the size and shape of the cavities. Most of the arthropods, including aquatic insects, are detritivores feeding on rotten debris which collects in the reservoirs of bromeliads. Also, some animals utilize epiphytes only as shelter. Epiphyte association with ants is largely correlated with the size and shape of the cavities. Intermediate steps between the ''phytotelm'' type and the ''myrmecophytic'' type were determined in the genus Tillandsia. The best rate of occupation by ants (96% of the ramets sheltered ants) was obtained by A. bracteata of the ''phytotelm tank'' type (reservoir in peripheric cavities, but also a waterproof central cavity), while the best rate of ant diversity was observed in T. bulbosa (''myrmecophytic'' type; 26 ant species). Ants sheltered in the bromeliads were shown to protect host trees against defoliation by an undetermined chrysomelid beetle and the leaf-cutting ant Atta cephalotes.