Are alien plants more competitive than their native conspecifics? A test using Hypericum perforatum L

Area of Science:

• Ecology
• Evolutionary Biology
• Plant Science

Background:

• The evolution of increased competitive ability (EICA) hypothesis suggests invasive plants may gain competitive advantages by losing costly defenses when freed from natural enemies.
• This reallocation of resources could enhance traits for superior competition.

Purpose of the Study:

• To test the EICA hypothesis by comparing the competitive ability of native and introduced St John's wort (Hypericum perforatum).
• To investigate if introduced populations, long free from natural enemies or under biological control, exhibit enhanced competitive ability.

Main Methods:

• Greenhouse experiment comparing native European St John's wort with introduced North American populations (central and western).
• Plants were grown with and without competition from Italian ryegrass (Lolium multiflorum).
• Interspecific competition and plant growth were quantified.

Main Results:

• Introduced St John's wort did not outperform native European genotypes in competitive ability.
• The impact of ryegrass competition on St John's wort was similar across native and introduced populations.
• Introduced plants did not show uniformly larger sizes; significant variability existed between populations.

Conclusions:

• The study's findings do not support the EICA hypothesis regarding enhanced competitive ability in introduced plants.
• Resource reallocation from defense to competition was not evident in the tested invasive St John's wort populations.
• Ecological interactions and evolutionary pressures in introduced ranges may not consistently lead to increased competitive superiority.