Native and alien species suffer from late arrival, while negative effects of multiple alien species on natives vary

Viktoria Ferenc,Frederik Zilles,Christian Merkert,Christine S Sheppard

doi:10.1007/s00442-021-05017-3

Abstract

Ongoing globalisation and climate change are causing plant species to invade new habitats and thereby alter biodiversity and ecosystem functioning. Since numbers of plant invasions continue to increase globally, it is crucial to investigate the effects of multiple co-occurring alien species on native communities. Furthermore, priority effects due to the earlier emergence of certain species affecting fitness of later arriving species can shape community structure and affect native species performance. We investigate in a common garden pot experiment the interactions among five alien-native species pairs. First we focus on the effect of growing with either one or two alien neighbour species on a native plant, second we alter the arrival time of the alien or native neighbour by 3 weeks. Generally, native species performance decreased when surrounded by two alien species compared to only one, although the magnitude of this effect varied depending on species, with one species even performing better with alien neighbours than in monoculture. Species performance greatly decreased when arriving second in the pot, for both native and alien species. In contrast, alien species tended to benefit more from arriving early. Given that we studied annual ruderal species, their potentially lower competitive ability might explain why we detected negative effects of late arrival. We highlight the need to further elucidate underlying mechanisms of small-scale invasion dynamics to achieve generalisations concerning the response of multiple alien and native plants given their species-specific differences in response to neighbour species and arrival time.

Highlights

Invasive species pose a major threat to biodiversity and ecosystem functioning (Pyšek et al 2020)
As the German floristic literature (Footnote Table 1) is inconsistent in categorising the species in native or archaeophytes, we considered archaeophytes (Solanum nigrum, Setaria pumila, Chenopodium album) as native species, given that their long history in central Europe makes it often difficult to distinguish between these categories (Scholz 2007)
While over all species the effect of two neighbours compared to one was negative (Table 2), we find Chenopodium album and Lapsana communis to strongly suffer from having two alien neighbour species (Fig. 1) while Solanum nigrum shows a weak negative response

Summary

Introduction

Invasive species pose a major threat to biodiversity and ecosystem functioning (Pyšek et al 2020). When multiple aliens are present, the following mechanisms might lead to stronger negative effects on a co-occurring native species: asymmetric competition meaning that the alien species compete less with each other than with the native species (Kuebbing and Nuñez 2016), or even facilitation among alien species (Flory and Bauer 2014) leading to higher negative impacts on the native species. The outcome of such an effect was termed ‘invasional meltdown’ by Simberloff and von Holle (1999)

Methods

Results

Discussion

Conclusion