Female-directed dispersal and facilitation between a tropical mistletoe and a dioecious host

Phoradendron hexastichum is a bird-dispersed mistletoe that infects the dioecious tree Cecropia schreberiana. Because both species share frugivore seed dispersers, we hypothesized that female Cecropia would have a greater probability and intensity of mistletoe infection than males due to more frequent visitation by shared frugivores. Over 50% of female Cecropia were infected, in contrast with 25% of males. On average, female trees had twice as many mistletoes as male trees. Infection probability and intensity increased with basal area in females but not in males, suggesting that lifetime reinfection was also female biased. We found mistletoe frugivores visiting uninfected fruiting females twice as often as males. Although mistletoes were mostly consumed by the mistletoe specialist Euphonia musica, we did not record Euphonia visiting uninfected Cecropia trees. Uninfected Cecropia trees were frequently visited by generalist frugivores (such as Spindalis portoricensis) that used both mistletoes and Cecropia fruits. The Cecroppia-frugivores-Phoradendron network of interactions seems to have led to the spatial linkage of the two plant species through directional dispersal, to plant-plant facilitation through shared frugivores. and to bird-bird facilitation in which generalist frugivores start new foci of infection that specialist frugivores can use.