Mistletoes as keystone species in pine woodlandsExploring the ecological consequences of a new interaction cocktail

Résumé

In this thesis, a study is made of the different roles that the European mistletoe (Viscum album subsp. austriacum) can play simultaneously in a Mediterranean pine forest, and their ecological consequences generating multiple plant–plant and plant–animal interactions in their ecosystem. Due to their hemiparasitic nature, the mistletoe has been traditionally regarded as a host pathogen, causing detrimental effects on growth, morphology, and reproduction. However, recently other ecological interactions that mistletoe establishes in the forest ecosystem have been found to be noteworthy, not only with its host but also with the rest of the community where they live. Consequently, the presence of mistletoe in the forest canopy can cause direct and indirect effects in their ecosystem through trophic and non– trophic relationships, favoring the restructure of community composition. Therefore, this thesis has been split into three main parts examining the role of mistletoe: I) as a keystone resource for its associated arthropods (Chapters 1–3); II) as direct competitor with its host (Chapters 4–5); and III) as indirect competitor with host–feeding herbivores (Chapter 6) and facilitator for the herbaceous community (Chapter 7). From a holistic view, it is concluded that mistletoes are keystone species that trigger a series of interactions with important ecological consequences at the community level, causing direct and indirect effects at different trophic levels. This has profound implications for the dynamics of the forest ecosystem, restructuring the entire community, from nutrient dynamics and herbaceous community to primary and secondary consumers. Thus, by simultaneously providing new resources while acting as a competitor and facilitator, mistletoes become ecosystem engineers, building an additional level of heterogeneity to the forest canopy and amplifying biodiversity and complexity in their ecosystem.