Evolution of increased Medicaco polymorpha size during invasion does not result in increased competitive ability

Area of Science:

• Ecology
• Evolutionary Biology
• Invasive Species Research

Background:

• Biological invasions present novel selection pressures driving rapid evolution.
• Hypotheses suggest introduced plants evolve larger sizes, enhancing competitive ability.
• Evidence for evolved larger sizes is mixed, with limited testing of competitive impacts.

Purpose of the Study:

• To investigate if introduced Medicago polymorpha genotypes exhibit evolved larger sizes compared to native genotypes.
• To determine if evolved size differences alter competitive responses or effects on native co-occurring species.
• To assess the role of evolved traits in invasion success.

Main Methods:

• Compared aboveground and belowground biomass of introduced and native Medicago polymorpha genotypes.
• Assessed competitive effects of both genotype groups on three common co-occurring native species.
• Conducted experiments under varying competition levels.

Main Results:

• Introduced genotypes produced significantly more aboveground (14%) and belowground (41%) biomass than native genotypes.
• These size differences were only apparent in the absence of competition.
• Competitive effects on native species were similar between introduced and native genotypes.

Conclusions:

• Evolutionary size increases in invasive Medicago polymorpha occurred post-introduction.
• Increased size did not translate to altered competitive effects on native species.
• Evolved larger size may enhance invasion success in disturbed or low-competition habitats.