Abstract

As a result of rapid environmental change caused by humans, species around the globe are expanding their ranges and spreading into uncharted territories at an unprecedented rate. Range- expansion of foundation species, or any species that plays a disproportionately large role in structuring ecosystems, can have severe impacts on recipient communities and ecosystems. Such species can not only alter biological diversity and ecosystem function, they can also interfere with the fundamental processes underpinning community assembly. However, despite large implications for the integrity and functioning of the world’s ecosystems, the ability of range expanders to alter community assembly processes is largely unknown. Here, we use an ongoing alpine invasion by a single foundation species (Pinus contorta) as a natural experiment to investigate the impacts of range-expansion on belowground community assembly and diversity. We report that abiotic selection exerts an increasingly strong influence as range expansion proceeds through the creation of micro-climatic islands with colder and wetter soils. Later stages of expansion were also associated with a decrease in the relative influence of dispersal and biotic interactions between fungi and their host plants. These changes, in turn, lead to an increase in the richness of fungal pathogens, and a decrease in the richness of symbionts, both locally and regionally. Taken together, these results suggest that range expanding species moving upslope have the potential to create novel ecosystems by rerouting the assembly of resident communities and reshaping biodiversity across scales. As climate change leads to poleward and upslope shifts in the distributions of plants and animals around the world, understanding the ecological processes through which range-expanders reshape native biodiversity can improve our predictions of the threats and challenges facing impacted ecosystems and enable better, more informed, conservation decisions.