Abstract
Invasive plants are sometimes considered to be more competitive than their native conspecifics, according to the prediction that the invader reallocates resources from defense to growth due to liberation of natural enemies [‘Evolution of Increased Competitive Ability’ (EICA) hypothesis]. However, the differences in competitive ability may depend on the identity of competitors. In order to test the effects of competitors, Ageratina adenophora plants from both native and invasive ranges competed directly, and competed with native residents from both invasive (China) and native (Mexico) ranges respectively. Invasive A. adenophora plants were more competitive than their conspecifics from native populations when competing with natives from China (interspecific competition), but not when competing with natives from Mexico. Invasive A. adenophora plants also showed higher competitive ability when grown in high-density monoculture communities of plants from the same population (intrapopulation competition). In contrast, invasive A. adenophora plants showed lower competitive ability when competing with plants from native populations (intraspecific competition). Our results indicated that in the invasive range A. adenophora has evolved to effectively cope with co-occurring natives and high density environments, contributing to invasion success. Here, we showed the significant effects of competitors, which should be considered carefully when testing the EICA hypothesis.
Highlights
Species Eschscholzia californica Hypericum perforatum Alliaria petiolata Silene latifolia Centaurea maculosa Dactylis glomerata Solidago canadensis Chromolaena odorata
When invasive A. adenophora plants competed with their native conspecifics, the decrease in aboveground biomass was significantly higher for the plants from invasive populations (Fig. 1b; Table 2)
When they competed with the natives from China, A. adenophora plants from invasive populations had significantly higher competitive ability than those from native populations (Fig. 2; Appendix. 2b)
Summary
Species Eschscholzia californica Hypericum perforatum Alliaria petiolata Silene latifolia Centaurea maculosa Dactylis glomerata Solidago canadensis Chromolaena odorata. Total biomass was not significantly different between A. adenophora plants from native and invasive ranges (Appendix 1a), the plants from invasive populations produced more aboveground biomass (Fig. 1a; Table 2).
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