Distribution of the invasive plant Taraxacum officinale at mediterranean altitudinal gradients: using niche models to infer whether cushion plants expand altitudinal range of this species

Abstract

Climatic conditions at higher altitudes pose a barrier to exotic species establishment due to an increase of the severity of climatic conditions, reducing plant survival and/or reproduction. However, processes that occur at lower spatial scale such as facilitation can expand the altitudinal range beyond that expected by climatic conditions alone. We tested this idea in Taraxacum officinale, a successful invasive plant that occur in Mediterranean ecosystems: California (Western USA) and central Chile among other regions based on the fact that facilitation effects on T. officinale (and other exotic plants) at higher altitudes have been widely documented for cushion plants. We used Ecological Distribution Models (EDMs) comparing a global niche model (a proxy of the fundamental niche), constructed with the totality of occurrences observed for this species worldwide with the regional niche model (a proxy of the realized niche, constructed with the occurrences observed in the invaded ranges): California and central Chile. This comparison allowed to infer the invasive stage at each invaded range. We also compared altitudinal distribution models predicted from global and regional niche model at each invaded region. Our result indicated that the regional niche model predicted areas not predicted by the global niche model, areas that coincide with the co-occurrences between T. offcinale and cushion plants. Moreover, regional niche models predicted an elevation range beyond that predicted by the global niche model. While plant facilitation process occurs locally, we propose that this process can scale-up to expand altitudinal distribution of invasive species. We emphasize the importance of predicting biological invasions not only from the perspective of climatic niche, but also including the effect of biological interactions.