Does enemy release matter for invasive plants? evidence from a comparison of insect herbivore damage among invasive, non-invasive and native congeners

Abstract

One of the most popular single-factor hypotheses that have been proposed to explain the naturalization and spread of introduced species is the enemy release hypothesis (ERH). One ramification of the ERH is that invasive plants sustain less herbivore damage than their native counterparts in the invaded range. However, introduced plants, invasive or not, may experience less herbivore damage than the natives. Therefore, to test the role of natural enemies in the success of invasive plants, studies should include both invasive as well as non-invasive introduced species. In this study, we employed a novel three-way comparison, in which we compared herbivore damage among native, introduced invasive, and introduced non-invasive Eugenia (Myrtaceae) in South Florida. We found that introduced Eugenia, both invasive and non-invasive, sustained less herbivore damage, especially damage by oligophagous and endophagous insects, than native Eugenia. However, the difference in insect damage between introduced invasive and introduced non-invasive Eugenia was not significant. Escape from herbivores may not account for the spread of invasive Eugenia. We would not have been able to draw this conclusion without inclusion of the non-invasive Eugenia species in the study.