Insect Herbivore Faunal Diversity among Invasive, Non-Invasive, and Native Eugenia Species: Implications for the Enemy Release Hypothesis

Hong Liu, Peter Stiling, Robert W. Pemberton, Jorge Pena

Abstract


The enemy release hypothesis (ERH) frequently has been invoked to explain the naturalization and spread of introduced species. One ramification of the ERH is that invasive plants sustain less herbivore pressure than do native species. Empirical studies testing the ERH have mostly involved two-way comparisons between invasive introduced plants and their native counterparts in the invaded region. Testing the ERH would be more meaningful if such studies also included introduced non-invasive species because introduced plants, regardless of their abundance or impact, may support a reduced insect herbivore fauna and experience less damage. In this study, we employed a three-way comparison, in which we compared herbivore faunas among native, introduced invasive, and introduced non-invasive plants in the genus Eugenia (Myrtaceae) which all co-occur in South Florida. We observed a total of 25 insect species in 12 families and 6 orders feeding on the six species of Eugenia. Of these insect species, the majority were native (72%), polyphagous (64%), and ectophagous (68%). We found that invasive introduced Eugenia has a similar level of herbivore richness as both the native and the non-invasive introduced Eugenia. However, the numbers and percentages of oligophagous insect species were greatest on the native Eugenia, but they were not different between the invasive and non-invasive introduced Eugenia. One oligophagous endophagous insect has likely shifted from the native to the invasive, but none to the non-invasive Eugenia. In summary, the invasive Eugenia encountered equal, if not greater, herbivore pressure than the non-invasive Eugenia, including from oligophagous and endophagous herbivores. Our data only provided limited support to the ERH. We would not have been able to draw this conclusion without inclusion of the non-invasive Eugenia species in the study.

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