Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Purple loosestrife provides long-distance pollinator attraction to a coflowering native species.

Abstract

Premise of research. The ecological impacts of invasive species on native ecosystems is a topic of intense debate. Recent reviews and meta-analyses have cast doubt on the long-held idea that the impacts of invasive species are universally negative. This may be particularly true in the case of plant-pollinator interactions. Here we describe a field experiment designed to assess the impact of an invasive species, Lythrum salicaria, on pollinator visitation to a commonly co-occurring native, Decodon verticillatus. Methodology. While controlling for total inflorescence density, we manipulated the presence of an invasive species, L. salicaria, at paired quadrats across several sites using a randomized block design. Data on the number, behavior, and taxon of pollinators visiting the quadrats were recorded during a series of observations spanning several days. Using linear models and paired t-tests, we analyzed the impact of the presence of the invasive species on the number of pollinators visiting D. verticillatus along with their visitation behavior in the quadrats. Pivotal results. The presence of L. salicaria was associated with significantly more pollinator visitors to a quadrat, both total visitors, and visitors to the native D. verticillatus. Conclusions. Our findings support the hypothesis that L. salicaria operates as a pollinator magnet and may in fact facilitate the long-distance attraction of pollinators to D. verticillatus in invaded communities. While this increase in visitation most likely has a positive impact on pollination of D. verticillatus, we note that the change in visitation may have negative implications for other animal-pollinated species in the vicinity. Our findings highlight the complexity and unpredictability of interactions among invasive and native species and help improve our understanding of how invasive species alter the short- and long-term dynamics of native plant and pollinator communities.