Approach to the invasive potential of Senecio pterophorus using SDMs and niche comparison analyses

Abstract

Senecio pterophorus DC. (Compositae) is a perennial shrub native to eastern South Africa (Eastern Cape and KwaZulu-Natal provinces) that inhabits forest margins, grasslands, and fynbos. One hundred years ago, S. pterophorus expanded into Western Cape in South Africa, but also cross-continentally into Australia. A more recent expansion occurred 25¿30 years ago in the Mediterranean Europe, concretely in Liguria (NW Italy) and Catalonia (NE Spain). In the introduced ranges, it mainly occurs in disturbed areas such as railroads or roadsides, although can also be found in natural areas. During the late 19th and the early 20th centuries, S. pterophorus was recorded in Belgium and the United Kingdom, respectively, although it is now considered extinct in both countries. We used species distribution models (SDMs) [geographic (G) space] and niche comparisons analyses [both in geographic and environmental (E) spaces] aimed to: (1) determine whether the species has changed its niche during the invasion process, and (2) ascertain why the species has not succeeded neither in Belgium nor in United Kingdom. In the G-space we used the maximum entropy algorithm (implemented in MaxEnt) to build niche distribution models, which are projected and evaluated in the native area vs. the invaded ones, and vice versa. Possible niche differences between native and invaded ranges were also assessed by several approaches (including the McCormack analysis and the PCA-env method of Broennimann). Additionally, metrics of niche overlap, similarity, expansion, and stability were calculated for each pairwise comparison native vs. invaded areas. An UPGMA dendrogram was performed to examine clustering groups and relationships between all realized niches. Finally, significant differences in means of environmental layers among niches were tested to determine which variables may explain the obtained niche shifts. The outcomes of this study would contribute to understand in which conditions S. pterophorus can lead to behave as a potential plant invasion.