Australian Acacia species have been widely planted worldwide for different purposes. Some of them have spread and altered the native ecosystem functions to the extent of being considered economic and ecologic threats. Understanding factors that allow these species to become invasive is an important step for mitigating or preventing the damaging effects of invasive species. We aimed to test the importance of native niche climatic width and average, plant functional traits (plant height, leaf area, seed mass and length of flowering season) and anthropogenic factors (number of uses, time since introduction) for predicting invasive success, in terms of abundance and range, of 16 Australian Acacia species in South Africa. By using multiple regression analysis, we constructed one different model for each type of predicting factors. When more than two predicting variables were available in a category, they were reduced to a maximum of two predictors by means of principal component analysis. Acacia spp. abundance and range in South Africa were highly correlated. The anthropogenic model (using number of human uses as predictor) was the best to explain both abundance and range of acacias in South Africa. This may be attributed to the importance of humans as dispersal vectors and to the relatively recent introduction of these species (circa 150 years). The functional traits model was the next best model explaining Acacia range, but not abundance, acacias with higher height and leaf area being more widespread in South Africa. Taller plants may disperse their seeds more efficiently by attracting dispersal agents, such as birds. The climatic affinities model was the following in the ranking explaining both range and abundance, acacias coming from moister, cooler and less seasonal regions in Australia being more successful in South Africa. This pattern may be attributed to the fast growth genotype generally selected for under low climatic stress conditions. Acacias with wide climatic niche in the native region were also more widespread and abundant in South Africa,
Question: Do invasions by invasive plant species with contrasting trait profiles (Arctotheca calendula, Carpobrotus spp., Conyza bonariensis, and Opuntia dillenii) change the climatic niche of coastal plant communities? Location: Atlantic coastal habitats in Huelva (Spain).
Methods:We identified the species composition of 216 paired (non-invaded and invaded) 10 × 10 m plots along the coast. For each species, we calculated its climatic niche based on the two main axis of a PCA constructed with nine climatic variables.We defined the community ensemble niche by the union of the overall climate niches of co-occurring species within a plot. We compared niche overlap metrics between non-invaded and invaded paired communities.
Results:There was an almost complete overlap in the community ensemble niches between non-invaded and invaded plots for the four invaders. Plots invaded by Carpobrotus spp. presented the lowest niche stability and those invaded by A. calendula had the highest. Plots invaded by Carpobrotus spp. showed the highest values of niche unfilling and expansion. In contrast, plots invaded by O. dillenii exhibited the lowest niche unfilling. Species similarity between non-invaded and invaded plots was on average 58%. The community ensemble niches differed depending on the invasive species and were related to differences in community species similarity between non-invaded and invaded plots. Overall, there was a positive correlation between community species similarity and climatic niche stability, and a negative correlation between community difference in taxonomic richness and climatic niche stability.Conclusions: Species assemblages in coastal vegetation did not change their community ensemble climatic niches after invasion by plants with contrasted life forms. This pattern is likely the result of invasion which did not trigger major changes in species richness and composition, or alternatively, because the species that were locally displaced by invasion have been substituted by others with similar climatic requirements.
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