Studies of the population ecology of the mistletoe Phoradendron anceps (Viscaceae) and its host Pisonia albida (Nyctaginaceae) in the Guanica forest reserve, Puerto Rico

I studied the spatial distribution and the demographic structure of the mistletoe Phoradendron anceps in relation to the distribution of its host (Pisonia albida), in a 5.29 ha plot in the Guanica forest. Both parasite and host species had an aggregated spatial pattern. The mistletoe spatial pattern was mainly explained by the host size and by dispersal. Larger Pisonia trees were generally more frequently and intensively parasitized than smaller trees. Parasitized trees were more prevalent in low-density stands than in high-density stands. Foraging and feeding behavior of Euphonia musica suggested that it could be the main dispersar of the mistletoe seeds. Seed dispersal appeared to be distance-limited. The demographic structure of the mistletoe was analyzed by considering the mistletoe population in the study plot as a metapopulation of mistletoe subpopulations on individual trees. Subpopulation structures were not correlated with the spatial distance between them. Six subpopulation structure patterns were identified. Apparently, larger subpopulations with a high number of reproductive individuals may be the sources of seeds not only for these subpopulations themselves but also for nearby subpopulations. The overall mistletoe metapopulation structure suggests that recruitment of young mistletoes has been relatively continuous over the past few years. The Phoradendron anceps-Pisonia albida system in Guanica best fits the habitat-tracking metapopulation model in which the habitat patches are dynamic.