Herbivory by an introduced Asian weevil negatively affects population growth of an invasive Brazilian shrub in Florida

Abstract

The enemy release hypothesis (ERH) is often cited to explain why some plants successfully invade natural communities while others do not. This hypothesis maintains that plant populations are regulated by coevolved enemies in their native range but are relieved of this pressure where their enemies have not been co-introduced. Some studies have shown that invasive plants sustain lower levels of herbivore damage when compared to native species, but how damage affects fitness and population dynamics remains unclear. We used a system of co-occurring native and invasive Eugenia congeners in south Florida (USA) to experimentally test the ERH, addressing deficiencies in our understanding of the role of natural enemies in plant invasion at the population level. Insecticide was used to experimentally exclude insect herbivores from invasive Eugenia uniflora and its native co-occurring congeners in the field for two years. Herbivore damage, plant growth, survival, and population growth rates for the three species were then compared for control and insecticide-treated plants. Our results contradict the ERH, indicating that E. uniflora sustains more herbivore damage than its native congeners and that this damage negatively impacts stem height, survival, and population growth. In addition, most damage to E. uniflora, a native of Brazil, is carried out by Myllocerus undatus, a recently introduced weevil from Sri Lanka, and M. undatus attacks a significantly greater proportion of E. uniflora leaves than those of its native congeners. This interaction is particularly interesting because M. undatus and E. uniflora share no coevolutionary history, having arisen on two separate continents and come into contact on a third. Our study is the first to document negative population-level effects for an invasive plant as a result of the introduction of a novel herbivore. Such inhibitory interactions are likely to become more prevalent as suites of previously noninteracting species continue to accumulate and new communities assemble worldwide.

Biological control and precipitation effects on spotted knapweed (Centaurea stoebe): empirical and modeling results

“…Our results join others in suggesting that the net contributions of seed reductions and increased plant mortality resulting from biological control can have population-level effects (Louda and Potvin 1995, Rose et al 2005, Eckberg et al 2012, Stricker and Stiling 2012. Biological control contributes to spotted knapweed populationlevel effects directly through reducing spotted knapweed seed production and plant survival and indirectly by decreasing spotted knapweed's ability to exploit favorable climatic conditions.…”

Joint effects of nutrient addition and enemy exclusion on exotic plant success

“…). To reliably quantify the impact of natural enemies on native and exotic species, experimental manipulation of enemy damage at the level of the plant community is a strong, but under‐utilized approach (e.g., Stricker and Stiling , Suwa and Louda ). However, because the community‐level approach only quantifies enemy impacts relative to competitors, testing for regulation by enemies at the population level would ideally be done by manipulating enemies in monocultures of each plant species.…”

An exotic herbivorous insect drives the evolution of resistance in the exotic perennial herb Solidago altissima

“…These findings will promote the understanding of how biological interactions after establishment are critical in shaping evolution in invasive plants. Finally, a growing number of studies are reporting interactions of exotic plants and exotic herbivorous insects in both natural (Ando et al 2010, Chang et al 2011, Stricker and Stiling 2012 and managed systems (Wheeler and Schaffner 2013). Although Garcia-Rossi et al (2003) pointed out that the large genotypic variation in plant tolerance to the original specialist planthopper Prokelisia marginata is likely to decrease effectiveness of biological control using the planthopper in the invasive Spartina spp.…”