Exotic plants accumulate and share herbivores yet dominate communities via rapid growth

Warwick J Allen,Jason M Tylianakis,Lauren P Waller,Ian A Dickie,Barbara I P Barratt

doi:10.1038/s41467-021-23030-1

Warwick J Allen, Jason M Tylianakis + Show 3 more

Open Access

https://doi.org/10.1038/s41467-021-23030-1

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Abstract

Herbivores may facilitate or impede exotic plant invasion, depending on their direct and indirect interactions with exotic plants relative to co-occurring natives. However, previous studies investigating direct effects have mostly used pairwise native-exotic comparisons with few enemies, reached conflicting conclusions, and largely overlooked indirect interactions such as apparent competition. Here, we ask whether native and exotic plants differ in their interactions with invertebrate herbivores. We manipulate and measure plant-herbivore and plant-soil biota interactions in 160 experimental mesocosm communities to test several invasion hypotheses. We find that compared with natives, exotic plants support higher herbivore diversity and biomass, and experience larger proportional biomass reductions from herbivory, regardless of whether specialist soil biota are present. Yet, exotics consistently dominate community biomass, likely due to their fast growth rates rather than strong potential to exert apparent competition on neighbors. We conclude that polyphagous invertebrate herbivores are unlikely to play significant direct or indirect roles in mediating plant invasions, especially for fast-growing exotic plants.

Highlights

Herbivores may facilitate or impede exotic plant invasion, depending on their direct and indirect interactions with exotic plants relative to co-occurring natives
Exotic herbivore biomass per mesocosm increased with the proportion of exotic species planted, while no relationship was observed for native herbivore biomass
Plant normalised degree did not differ between native and exotic plants (F1,48 = 1.35, P = 0.251; Fig. 2D and Supplementary Table 7), herbivore species richness of mesocosms increased with the proportion of exotic species planted in the community

Summary

Introduction

Herbivores may facilitate or impede exotic plant invasion, depending on their direct and indirect interactions with exotic plants relative to co-occurring natives. One research method has focused on comparing important invaders with congeneric native species[16,17,18,19], frequently finding support for invader escape from enemies[5] Despite this being a wellreasoned approach, the majority of studies to date have examined a relatively low diversity of plants and enemies from the community (see Supplementary Table 1 for sample sizes of species from studies used in the Meijer et al 2016 analysis7), leaving it unclear whether plant–herbivore interactions systematically favour exotic species. This may be especially true for exotic plant species, which can mitigate herbivore impacts via typically fast growth rates[29] and high tolerance of herbivory[30]

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