Neutral effect of an invasive plant species with specialized flower structure on native pollinator communities

Viktor Szigeti,Anikó Kovács-Hostyánszki,Boglárka Berki,Zoltán Soltész,Annamária Fenesi

doi:10.1007/s10530-020-02305-6

Abstract

Invasive plants modify native plant communities with serious consequences on plant-pollinator interactions. Invasion by common milkweed (Asclepias syriaca L.) threatens natural and agricultural habitats in Europe, with unknown effects on pollinators. Its special flower structure, habitat requirements and phenology offer novel insights into pollination ecology aspects of plant invasion. We compared flowering plant and pollinator communities between invaded and control sites, and the flower visitors between native plants and common milkweed. Wild bees and hoverflies did not differ in abundance, diversity and community composition between the invaded and control sites. However, honey bees and bumble bees preferred milkweed above native plants during milkweed flowering. In contrast to many studies, our results suggest neutral effect of plant invasion on the sampled aspects of diurnal wild pollinator community, while providing resources for a few pollinator taxa. This neutral effect might be explained by the long-term, wide scale distribution of milkweed and/or its typically relatively low coverage compared to many other invasive plants, enabling the persistence of some native flowering species. However, its special flower structure offers nectar only for a few common pollinators, including honey bee, and it decreases abundance of native flowers in spring with unknown consequences on wild bees’ reproduction success. Despite the lack of direct negative effects on wild pollinators, restoration of invaded habitats to promote native floral communities is suggested to enable diverse, longer lasting foraging resources for wild pollinators and honey bees. Promoting actively wildflower habitats might be vital for beekeepers in the case of milkweed eradication.

Highlights

Invasive plant species often profoundly modify the abundance and the diversity of native plant species, and sustain an alternative vegetation state by halting the trajectory of succession (Meiners et al 2002; Cramer et al 2008; Fenesi et al 2015)
We studied whether there is any competition between milkweed and native plants for pollination, namely whether milkweed was visited by different wild bee species or is it likely to attract more bumble bees and honey bees than native flowers
To study whether milkweed was visited by different wild bee species than native flowers and to indicate any competition between milkweed and the native plants for flower visitors, we performed two analyses

Summary

Introduction

Invasive plant species often profoundly modify the abundance and the diversity of native plant species, and sustain an alternative vegetation state by halting the trajectory of succession (Meiners et al 2002; Cramer et al 2008; Fenesi et al 2015) Such changes on plant communities can have an impact on the related animal communities, such as pollinator insects and their pollination service (Bezemer et al 2014; Traveset and Richardson 2014; van Hengstum et al 2014). The altered pollinator community can further boost the plant invasion: the reduced pollinator visits and/or pervasive inter-specific pollen transfer decrease reproduction success and diversity of the native flora (Chittka and Schurkens 2001; Carvalheiro et al 2014; but see Charlebois and Sargent 2017), and increase the reproduction success on the highly visited invasive plant species (Stout and Tiedeken 2017)

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