As a result of global change, many species are expanding their geographic ranges, sometimes colonizing entirely new areas and interacting with resident communities. However, the influence of range-expanders on the re-assembly of these newly created communities is poorly understood. Alpine communities are specifically prone to range expansion, as the general warming of the planet likely alleviates some of the environmental filters limiting expansion into these communities. The predicted movement of species into the alpine is innately focused on arboreal taxa, due to their structuring role as foundation species, and their ability to cause ecosystem-wide impacts as range-expanders. Here, we study a recent invasion of Pinus contorta (Lodgepole Pine) into a treeless alpine community in Patagonia (Argentina), to investigate the initial impacts of range expansion from a community perspective. Specifically, we ask the question: Can a range-expanding species alter the processes responsible for community assembly in alpine environments? To answer this question, we quantified the structure of plant-associated fungal communities along a chronosequence of range expansion. We then modelled the relationship between compositional turnover and either spatial distances or micro-habitat differences to assess the relative influence of stochastic and deterministic assembly processes.
Results/Conclusions
In the absence of invasive pines, plant-associated fungal communities were shaped by stochastic, spatial processes, such as dispersal limitations. However, the presence and age of range-expanding P. contorta increased the importance of deterministic assembly processes. Specifically, plant-associated fungal communities beneath adult pines were almost completely dependent on deterministic processes, suggesting a range-expanding species can lead to homogenization of ß-diversity across fine spatial scales. The availability of soil organic matter (Carbon) and soil moisture determined to a large extent the compositional turnover of fungal communities in the presence of pines. Changes in these soil characteristics are generally associated with pine establishment and growth, indicating that a single range-expanding species can influence ecosystem processes, and in turn, fundamentally alter community assembly. As alpine ecosystems become increasingly threatened by climate warming and species range expansion, these results help us understand the initial ways range-expanding species shape novel community assembly, enabling researchers to better predict the composition, structure and functionality of future alpine communities