Multiple global-change drivers and cascading effects in Mediterranean ecosystems: Lessons from an iconic national park

Historically, Mediterranean systems, particularly the Mediterranean Basin, have been substantially impacted by multiple regional-scale disturbances resulting from complex interactive effects of global-change drivers. However, such effects are typically studied on isolated groups of organisms, often disregarding how ecological processes such as biotic interactions affect ecosystem responses to global change. We use the Doñana Protected Area, one of the most important wetlands and shrublands in Europe, as a well-documented case study to highlight how regional anthropogenic pressures simultaneously affect various interacting species, creating cascading impacts across trophic webs on different ecosystems. Using two examples representing the role of key habitat-structuring species on ecosystem processes, the cork oak (Quercus suber) and European rabbit (Oryctolagus cuniculus), we show how abundance decreases of such key species due to interlinked direct and indirect anthropogenic pressures can alter multitrophic communities – but not always negatively, as other species can adapt to the loss of key species. We also use two examples of species that have flourished under human pressures, the native wild boar (Sus scrofa) and invasive red swamp crayfish (Procambarus clarkii), and how their abundance increases have had complex impacts on ecosystems. We then discuss, based on the outcomes of actual conservation actions, how management targeted at single species or taxa is ineffective for ecosystem functioning, as it ignores complex interlinks with other components of the system. Instead, the ecosystem-wide impacts of gain and losses of interacting species serves as an excellent empirical example for the need for conservation management and research agenda that account for the complexity of global change in the Mediterranean.