The abundance and distribution of bird dispersed mistletoes in a community can be influenced by the foraging behavior of birds, the structure of plant communities, and the identity of host trees. However, the relative contribution of these factors shaping mistletoe demographic patterns in landscapes is still little studied. We conducted a study in Puerto Rico to quantify the relative contribution of variables affecting dispersal limitation such as host phenology pattern, host abundance, and seed dispersal by birds with variables related to host suitability affecting recruitment limitation and shaping the abundance and distribution of mistletoes. We hypothesize that the abundance and distribution of mistletoes will be strongly correlated with overlapping phenologies between mistletoes and hosts. During three years, we collected data on plant phenology, bird behaviour, and seed rain. We also conducted a demographic survey to document mistletoe host usage patterns, and a seed addition experiment to document the ability of mistletoes to grow on common bird dispersed trees at the site.
Results/Conclusions
The most important component influencing mistletoe abundance and distribution was the fruiting intensity of trees in the community, followed by the quality of hosts. We also found that distribution of mistletoes on hosts was not at random. The seed addition experiment shows that survival of mistletoes on their most common host at the study site is very low compared to survival on experimental hosts. However, the few survivors grew faster and larger than almost all other mistletoe seedlings planted on experimental hosts. Our results suggest that the observed host usage pattern of mistletoes is strongly shaped by host phenology, whose fruiting patterns combined with feeding preferences of bird dispersers determines where mistletoe seeds are being deposited. We also show that continuous deposition of mistletoe seeds by birds on a host can compensate for low survival rates. Mistletoes and other parasitic plants are often found in nature parasitizing only a subset of all suitable hosts available. Here we show that patterns of parasitism between mistletoes and hosts can be strongly shaped by the interactions among phenology and bird behaviour in a community, and the quality of hosts plants.