Host associations of the strangler fig Ficus watkinsiana in a subtropical Queensland rain forest

The distribution of epiphytic organisms is limited by the availability of, and dispersal to suitable hosts. We examined the distribution of a hemi-epiphytic strangler fig, Ficus watkinsiana (Moraceae) in Cooloola National Park (Queensland, Australia), in order to determine whether this species exhibits a preference for certain host species and why. We assessed host bark roughness and flakiness, fruit type, and size to explain the observed distribution of F. watkinsiana. We surveyed over 1900 potential host trees of the 30 most common forest canopy species and found that host size measured by diameter at breast height accounted for most variation in fig prevalence (Binary Logistic Regression log-likelihood = -588.178, G= 314.494, d.f. = 1, P< 0.005). After controlling for host size, F. watkinsiana prevalence still differed significantly between host species (X 2 = 54.612, d.f. = 24, P < 0.005), a difference that was only partly explained by variation in the bark roughness of host trunks. These results suggest that variation in the rate at which tree species host strangler figs are primarily related to individual tree size - figs may simply be more likely to colonize and thrive upon host species that grow larger.