SEED DISPERSAL OF TRILLIUM OVATUM (LILIACEAE) IN SECOND-GROWTH REDWOOD FORESTS

Trillium ovatum (Liliaceae) is myrmecochorous: its seeds bear large elaiosomes that are attractive to ants. Nevertheless, in coastal second-growth redwood forests of northern California, most seedlings occur in mixed-age clusters close to potential parents, suggesting that seed dispersal is limited. Ants were absent or rare at two relatively cool, moist study sites. At these sites, most seeds either eventually fell passively from fruits or were knocked to the ground by banana slugs that foraged on the elaiosomes. At two warmer, drier sites, a single species of ant, Lasius pallitarsis, dispersed the seeds but tended to remove the elaiosomes before returning to the nest. Thus at all sites a large number of seeds remained close to adults, accounting for the observed pattern of seedling distribution. The dispersal adaptations of T. ovatum and other redwood forest myrmecochores probably evolved in forests where seed-carrying ants were more common.