Parasitic plants in Europe: ecological niches and spatial patterns.

Parasitic plants inhabit a wide range of ecosystems worldwide, where they may have critical roles as "ecosystem engineers". We examined the ecology of parasitic plants in Europe. We aimed to identify habitat preferences, spatial distribution, and environmental drivers of parasitic plant functional types: euphytoid hemiparasites, obligate root parasites, and parasitic vines, and assess individual species' ecological niches. We analysed 244 parasitic plant species in a dataset of 819,452 vegetation plots across European natural vegetation. We used a boosted regression tree model to assess the effects of macro-climate, topography, and habitat descriptors (open, wet, saline) on the distribution of parasitic plant functional types. We analysed their distribution along the gradients of ecological indicator values. Finally, we determined the niches of individual species along all the environmental gradients. Parasitic plants occur across Europe and in nearly all habitats. Euphytoid hemiparasites (173 species) are most abundant in colder environments with moderate to high precipitation and low precipitation seasonality. In contrast, obligate root parasites (52 species) and parasitic vines (12 species) are primarily associated with warm-temperate to Mediterranean dry climates. All three functional types prefer nutrient-poor to moderately rich conditions. Some species diverge from the trend of their functional type. The spatial distribution and niches of parasitic plant functional types correspond to their fundamental physiological properties, including mode of resource acquisition and level of photosynthesis. Euphytoid hemiparasites are likely to be negatively affected by climate warming, while obligate root parasites and parasitic vines might benefit from future warmer and drier climates.