Increased plant size in exotic populations: A common graden test with 14 invasive species

Authors: Blumenthal, Dana; HUFBAUER, RUTH - COLORADO STATE UNIVERSITY

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2007
Publication Date: 11/15/2007
Citation: Blumenthal, D.M., Hufbauer, R. 2007. Increased plant size in exotic populations: A common graden test with 14 invasive species. Ecology 88:2758-2765.

Interpretive Summary: Understanding why invasive species are so successful is a key step in developing long-term strategies to control their populations. One factor that may contribute to invasive species success is rapid evolution following introduction to a new range. The evolution of increased competitive ability (EICA) hypothesis suggests that with few natural enemies, exotic plants (i.e., plants introduced from other continents) will evolve to allocate resources to growth or reproduction instead of defense against enemies. Previous studies generally support the prediction that exotic plants will be less well defended than native plants. However, results are mixed with respect to the question of whether lower defenses have allowed exotic plants to become more competitive. In a common garden experiment involving 14 different invasive species, we tested whether exotic plants generally grow larger than native plants, and whether any differences depend on the intensity of competition. We found a surprisingly consistent pattern of larger exotic than native plants, but only in the absence of competition. These results provide broad support for the EICA hypothesis, but are also in accord with suggestions that traits other than competitive ability per se may be evolved in a species’ exotic range.

Technical Abstract: The evolution of increased competitive ability (EICA) hypothesis suggests that in the absence of enemies, exotic plants will lose costly defenses in favor of competitive ability. Previous studies generally support the prediction that exotic plants will be less well defended than native plants. However, results are mixed with respect to the question of whether lower defenses have allowed exotic plants to become more competitive. In a common garden experiment involving 14 different invasive species, we tested whether exotic plants generally grow larger than native plants, and whether any differences depend on the intensity of competition. We found a surprisingly consistent pattern of larger exotic than native plants, but only in the absence of competition. These results provide broad support for the EICA hypothesis, but are also in accord with suggestions that traits other than competitive ability per se may be evolved in a species’ exotic range.