Ecophysiological plasticity and local differentiation help explain the invasion success of Taraxacum officinale (dandelion) in South America

Plasticity and local adaptation have been suggested as two main mechanisms that alien species use to successfully tolerate and invade broad geographic areas. In the present study, we try answer the question if the mechanism for the broad distributional range of T. officinale is for phenotypic plasticity, ecotypic adaptation or both. For this, we used individuals of T. officinale originated from seeds collected in five localities along its latitudinal distribution range in the southern‐hemisphere. Seedlings were acclimated at 5 and 25°C for one month. After the acclimation period we evaluated ecophysiological and cytogenetic traits. Additionally, we assessed the fitness at each temperature by recording the seed output of individuals from different localities. Finally, we performed a manipulative experiment in order to assess the tolerance to herbivory and competitive ability between T. officinale from all origins and Hypochaeris scorzonerae a co‐occurring native species. Overall, individuals of T. officinale showed high plasticity and ecotypic adaptation for all traits assessed in this study. Changes both in physiology and morphology observed in T. officinale from different origins were mostly correlated, enhancing their ecophysiological performance in temperatures similar to those of their origin. Additionally, all localities showed the same chromosome number and ploidy level. On the other hand, all individuals showed an increase the seed output at 25°C, but those from northern localities increased more. T. officinale from all origins was not significantly affected by herbivory while native showed a negative effect. On the other hand, T. officinale exerted a strong negative effect on the native species, but this former not effected significantly to the invasive T. officinale. High plasticity and local adaptation in all ecophysiological traits, seed‐set and the low cytogenetic variability in T. officinale suggests that both strategies are present in this invasive plant species and are not mutually exclusive. Finally, higher tolerance to herbivory and competitive ability suggests that T. officinale could perform successfully in environments with different climatic conditions, and thus colonize and invade South‐America.     

Disturbance reinforces community assembly processes differentially across spatial scales

Background and AimsThere is a paucity of empirical research and a lack of predictive models concerning the interplay between spatial scale and disturbance as they affect the structure and assembly of plant communities. We proposed and tested a trait dispersion-based conceptual model hypothesizing that disturbance reinforces assembly processes differentially across spatial scales. Disturbance would reinforce functional divergence at the small scale (neighbourhood), would not affect functional dispersion at the intermediate scale (patch) and would reinforce functional convergence at the large scale (site). We also evaluated functional and species richness of native and exotic plants to infer underlying processes. Native and exotic species richness were expected to increase and decrease with disturbance, respectively, at the neighbourhood scale, and to show similar associations with disturbance at the patch (concave) and site (negative) scales.MethodsIn an arid shrubland, we estimated species richness and functional dispersion and richness within 1 m² quadrats (neighbourhood) nested within 100 m² plots (patch) along a small-scale natural disturbance gradient caused by an endemic fossorial rodent. Data for the site scale (2500 m² plots) were taken from a previous study. We also tested the conceptual model through a quantitative literature review and a meta-analysis.Key ResultsAs spatial scale increased, disturbance sequentially promoted functional divergence, random trait dispersion and functional convergence. Functional richness was unaffected by disturbance across spatial scales. Disturbance favoured natives over exotics at the neighbourhood scale, while both decreased under high disturbance at the patch and site scales.ConclusionsThe results supported the hypothesis that disturbance reinforces assembly processes differentially across scales and hampers plant invasion. The quantitative literature review and the meta-analysis supported most of the model predictions.