Abstract
Biological control agents may have unintended effects on native biota, particularly species that are closely related to the target invader. Here, we explored how Chrysolina quadrigemina, a beetle introduced to control the invasive weed Hypericum perforatum, impacts native H. punctatum in Tompkins County, New York, USA. Using a suite of complementary field surveys and experimental manipulations, we examined beetle preference for native and exotic Hypericum species and whether beetle herbivory influences the spatial distribution of H. punctatum. We found that the introduced beetle readily consumes native H. punctatum in addition to its intended target, and that H. punctatum at our field sites generally occurs along forest edges despite higher performance of experimental plants in more open habitats. However, we found no evidence that the beetle limits H. punctatum to forest edge habitats.
Highlights
Invasions by exotic species can negatively impact native communities through altered species interactions and ecosystem processes (Mack et al, 2000)
We asked (1) do beetles preferentially exploit the native or exotic Hypericum species, (2) is beetle herbivory concentrated in sunny areas, and (3) does beetle herbivory limit the distribution of H. punctatum and H. perforatum?
Amongst naturally-occurring Hypericum, we found that natives on average had heavy damage on 23% of leaves compared to only 13% of leaves on the exotic (Fig. 2A) and this trend was consistent with distance from the forest edge (Fig. 3A)
Summary
Invasions by exotic species can negatively impact native communities through altered species interactions and ecosystem processes (Mack et al, 2000). A logical way to combat invasive species is through biological control, the practice of releasing specialist enemies, typically from the original range of the invader, to control the spread of the exotic species (McFadyen, 1998; Van Driesche et al, 2010). Because the traits mediating plant-herbivore interactions, such as plant chemical defenses, are often phylogenetically conserved (Futuyma & Agrawal, 2009), most herbivores readily utilize several closely related plants (Jaenike, 1990; Pearse & Altermatt, 2013).
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