Are range limits concordant with climatic niche requirements in alien plants? Leguminous invasive plants as case study, along a latitudinal gradient, central Chile

How do species reach the limits of their distribution and what prevents their continued expansion beyond these ranges? Exotic plant species represent a natural experiment to answer these questions. If climate is the limiting factor, then one would expect a matching between the observed range limit for a species and the range limit predicted by its climatic niche. If there is no matching, then other factors such as dispersal limitation, competition or facilitation come into play. In this work, the predicted and observed range limits for eight exotic legume species were compared: Acacia dealbata , Acacia melanoxylon , Cytisus striatus , Teline monspessulana , Ulex europaeus , Lotus corniculatus , Trifolium suffocatum and Vicia villosa , in a latitudinal gradient in Chile. For the estimation of the observed range limit (North and South), absence/presence data were obtained from 30° to 43.1° south latitude. For the estimation of the predicted range limits, GBIF presence data were used to construct the global climatic niches, identifying suitable climatic zones (presences) and unsuitable climatic zones (absences). With this information, presence probability models were constructed with hierarchical Huisman-Olff-Fresh (HOF) regression, from which the predicted range limits (North and South) were obtained. Our results suggest that the species Acacia dealbata and Cytisus striatus have reached their predicted edge at the northern and at the southern end of the gradient. The rest of the species have not yet reached this limit across both geographic edges. At the southern end of the gradient, most species have not reached the limit predicted by the climatic niche; except for Cytisus striatus whose observed range limit is higher than predicted. Factors other than climate are discussed to explain the discrepancies between observed and predicted range limits.