Indirect positive effects of a parasitic plant on host pollination and seed dispersal

Parasitic plants often have a strong fitness-impact on their plant hosts through increased host mortality and reduced or complete suppression of reproduction. Tristerix corymbosus (Loranthaceae) is a hemiparasitic mistletoe that infects a wide range of host species along its distribution range. Among such species, Rhaphithamnus spinosus (Verbenaceae) is a frequent host with a flowering and fruiting season partially synchronized with mistletoe reproductive phenology. As parasitized hosts have, in principle, a larger flower display and fruit crop size than non-parasitized hosts, we examined whether host and parasite reproductive synchrony make infected hosts more attractive for pollinators and seed dispersers than uninfected hosts. Our results showed that pollinator visit rates did not differ between parasitized and non-parasitized hosts. Conversely, seed rain was higher in parasitized than non-parasitized individuals. The number of seeds fallen under non-parasitized plants was spatially associated with crop size, while parasitized plants did not show such association. Finally, the number of seedlings of R. spinosus was significantly larger near parasitized than non-parasitized hosts. Our results suggest that the presence of the mistletoe might be responsible of the higher reproductive success showed by the parasitized fraction of R. spinosus. This effect, however, seems to be related to seed dispersal processes rather than pollination effects.