Differing impacts of two major plant invaders on urban plant-dwelling spiders (Araneae) during flowering season

Tobias Bauer,Jens Schirmel,Fabian Kempfer,Daria Alison Bäte

doi:10.1007/s10530-020-02452-w

Abstract

Plant invasions can have major impacts on ecosystems and influence global species diversity. In Central Europe, Himalayan balsam (Impatiens glandulifera) and American goldenrods (Solidago canadensis and S. gigantea) are important invaders often establishing dense and homogeneous stands, especially in urban and other disturbed habitats. We investigated their impacts on plant-dwelling spiders (abundance, family structure, guild structure) and potential spider prey items during flowering season within an urbanized landscape using a paired design comparing invaded and native reference vegetation plots. In general, flowering American goldenrods and Himalayan balsam had no significant impacts on the spider family composition. Invasion of American goldenrods further had no effect on total spider abundance and potential prey item abundance. In contrast, goldenrods showed a significantly increased crab spider (Thomisidae) abundance while being less inhabited by web builders. Himalayan balsam negatively influenced free hunters and running crab spider (Philodromidae) abundance, while we found no effects on other groups and total spider abundance. For Himalayan balsam, potential prey item abundance was higher than in native vegetation stands. Notwithstanding that our results only represent a snapshot of the system, they suggest that large-scale removal of urban goldenrod stands during flowering season might negatively influence local spider abundance, especially of crab spiders. Management efforts should therefore be accompanied by compensation measures to avoid disruptive effects on local plant-dwelling spider communities.

Highlights

Biological invasions can have tremendous ecological and socio-economic consequences (Sala et al 2000; Nentwig et al 2018)
Himalayan balsam negatively influenced free hunters and running crab spider (Philodromidae) abundance, while we found no effects on other groups and total spider abundance
In our studied urban environments, we found contrasting impacts of flowering American goldenrods and Himalayan balsam on plant-dwelling spiders

Summary

Introduction

Biological invasions can have tremendous ecological and socio-economic consequences (Sala et al 2000; Nentwig et al 2018). Invasive alien plant species are one of the major drivers of current global biodiversity erosion (Bellard et al 2016; Simberloff et al 2013), yet their eradication can result in enormous costs (Hoffmann and Broadhurst 2016; Pimentel et al 2005). Invasive plants have negative effects on animal diversity, fitness and abundance (Schirmel et al 2016). Herbivore communities are often directly affected by alien plant invasions due to loss of indigenous vegetation Invasive plants can negatively affect predator communities by altering habitat conditions (e.g., Balkenhol et al 2018; Gerber et al 2008) and might lower foraging success of some predators (Maerz et al 2005)

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