Release from herbivory does not confer invasion success for Eugenia uniflora in Florida

Abstract

One of the most commonly cited hypotheses explaining invasion success is the enemy release hypothesis (ERH), which maintains that populations are regulated by coevolved natural enemies where they are native but are relieved of this pressure in the new range. However, the role of resident enemies in plant invasion remains unresolved. We conducted a field experiment to test predictions of the ERH empirically using a system of native, introduced invasive, and introduced non-invasive Eugenia congeners in south Florida. Such experiments are rarely undertaken but are particularly informative in tests of the ERH, as they simultaneously identify factors allowing invasive species to replace natives and traits determining why most introduced species are unsuccessful invaders. We excluded insect herbivores from seedlings of Eugenia congeners where the native and invasive Eugenia co-occur, and compared how herbivore exclusion affected foliar damage, growth, and survival. We found no evidence to support the ERH in this system, instead finding that the invasive E. uniflora sustained significantly more damage than the native and introduced species. Interestingly, E. uniflora performed better than, or as well as, its congeners in terms of growth and survival, in spite of higher damage incidence. Further, although herbivore exclusion positively influenced Eugenia seedling survival, there were few differences among species and no patterns in regard to invasion status or origin. We conclude that the ability of E. uniflora to outperform its native and introduced non-invasive congeners, and not release from insect herbivores, contributes to its success as an invader in Florida.

No release for the wicked: enemy release is dynamic and not associated with invasiveness

“…For example, in a study of 12 temperate vine species, native and invasive vines experienced more foliar damage from Table A1. insect and mammal herbivores than noninvasive exotics, not supporting ERH predictions (Ashton and Lerdau 2008). Similarly, invasive Eugenia uniflora sustained more insect herbivore damage than congeneric native and noninvasive exotic species in a common garden experiment, also not supporting Predictions 1 and 2 (Stricker and Stiling 2014). In a study using 18 clover species, introduced and native species experienced similar amounts of disease, and the most invasive introduced species experienced the most disease (Parker and Gilbert 2007).…”

“…Given the dual roles enemies play in invasions, homogenizing invasive and noninvasive exotic species into one group could miss important information on the drivers of invasiveness, and thus provide only a conservative estimate for whether invasive species experience enemy release. Studies that do not differentiate between these two types of introduced species have found that introduced plants receive less (Agrawal et al 2005), no difference (Agrawal and Kotanen 2003, Hawkes 2007, Chun et al 2010, or more (Ashton andLerdau 2008, Stricker andStiling 2014) enemy damage compared to natives. These same patterns are found in studies looking at enemy abundance or the performance consequences of enemy damage (reviewed in Colautti et al 2004).…”

Phenology in a warming world: differences between native and non‐native plant species

“…The non‐native species are all from outside the United States, based on herbarium or historical records (Michigan Flora [http://michiganflora.net], Consortium of Midwest Herbaria [http://midwestherbaria.org/portal/]). We further categorised non‐native species as invasive or non‐invasive exotic, because differentiating between these two types of non‐native species can yield important information on the drivers of invasiveness (Agrawal et al ; Stricker & Stiling ; Schultheis et al ). Species were characterised as invasive (here defined as widespread and damaging non‐native species) if they were listed on one or more of the following as of June 2014: (1) Michigan Natural Features Inventory (Borland et al ), (2) Czarapata () list of ‘major invader[s] of natural areas’ not needing disturbance to establish, (3) Wild Type Plants (http://www.wildtypeplants.com) and (4) the Michigan Seed Law (Act 329 of 1965) (http://www.michigan.gov/).…”

Is Enemy Release Strong for Invasive Plants?

“…Similarly, invasive Eugenia uni ora in south Florida exhibited more insect damage than native or non-invasive exotic Eugenia spp. in common gardens (Stricker and Stiling, 2014). More recent reviews are also mixed.…”