Secondary foundation species foster novel plant-animal interactions in the forest canopy: evidence from mistletoe

Forest canopies provide the initial physical and biological framework to secondary, dependent species, such as parasitic plants. In a Mediterranean pine forest, we have taxonomically and functionally characterised the entire arthropod community that interacts with mistletoe during its flowering period. We hypothesise that a secondary foundation species such as mistletoe enhances the arthropod diversity and abundance, fostering novel plant-animal interactions in the canopy. Our results clearly show contrasting guilds of herbivores (highly specialised) and floral visitors (highly generalist) with markedly different taxonomic and ecological profiles, the latter determining the fruit set of the mistletoe. By acting as a secondary foundation species, mistletoe, during flowering, increases the diversity and abundance of newcomers in the pine canopy. New species attracted to the canopy include a specialised herbivore,Cacopsylla visci, and a diverse guild of floral visitors, including the orders Hymenoptera, Diptera, Hemiptera, and Lepidoptera. In conclusion, mistletoe creates conditions that support the co-occurrence of functionally distinct organisms in the canopies, fostering pine forest biodiversity and complexity of ecological interactions.