Abstract:   Habitat fragmentation, changes in land use, defaunation, and species introductions mediated by human activities are driving a global environmental degradation at an unprecedented pace and geographic scale has critically impacted not only species performance and distribution, but also their ecological interactions with other species in the community and thus the ecosystem services they provide. In particular, hunting and other human activities have caused marked reductions or even extinction of numerous populations of many vertebrate species, this process being known as defaunation. Interesting, other human activities (e.g. predator removal, habitat management, reserves creation) have greatly augmented the density of some wild ungulates such as red deer and wild boar (i.e. overfaunation"). Even more pervasive and studied is the spread of alien invasive species which are often triggered by the worldwide intense merchandise trade of countless plant and animal species, paired to the augmented disturbances on many ecosystems. The individual impacts of these three types of perturbations (defaunation, overfaunation, biological invasions) on ecosystem composition and functioning have been generally well-investigated. Surprisingly, however, there is a important gap of knowledge concerning how these three factors interact with each other leading to potential synergies and non-additive effects. We propose to investigate the intertwined effects of defaunation and overfaunation on the seed dispersal kernels and recruitment of three representative Mediterranean plant species all dispersed by mammal species which populations are either locally declining or augmenting in some areas of the Doñana National Park (SW Spain). To this end, we combine available long-term comprehensive field data, molecular analyses (to estimate seed dispersal distances), and individual-based, spatially explicit simulation models to evaluate the consequences for plant dispersal and recruitment of different scenarios of defaunation and overfaunation. Further, we will also consider a less known system, located in Mallorca island (E Spain), to investigate the combined effect of an introduced pest and overabundant domestic ungulates on Chamaerops humilis reproductive success, as well as on the palm interactions with subsequent animal associates (pollinators, seed dispersers, seed predators). The general objective of this proposal is thus to quantify the joint effect of defaunation, overabundance of ungulates, and the introduction of invasive pests on the dynamics of several Mediterranean plant populations. To our knowledge, this is the first time that such intertwined effects will be comprehensively investigated.