Direct and Indirect Influence of Non-Native Neighbours on Pollination and Fruit Production of a Native Plant.

Ana Montero-Castaño,Montserrat Vilà,Harald Auge

doi:10.1371/journal.pone.0128595

Ana Montero-Castaño, Montserrat Vilà + Show 1 more

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https://doi.org/10.1371/journal.pone.0128595

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Abstract

BackgroundEntomophilous non-native plants can directly affect the pollination and reproductive success of native plant species and also indirectly, by altering the composition and abundance of floral resources in the invaded community. Separating direct from indirect effects is critical for understanding the mechanisms underlying the impacts of non-native species on recipient communities.ObjectivesOur aims are: (a) to explore both the direct effect of the non-native Hedysarum coronarium and its indirect effect, mediated by the alteration of floral diversity, on the pollinator visitation rate and fructification of the native Leopoldia comosa and (b) to distinguish whether the effects of the non-native species were due to its floral display or to its vegetative interactions.MethodsWe conducted field observations within a flower removal experimental setup (i.e. non-native species present, absent and with its inflorescences removed) at the neighbourhood scale.ResultsOur study illustrates the complexity of mechanisms involved in the impacts of non-native species on native species. Overall, Hedysarum increased pollinator visitation rates to Leopoldia target plants as a result of direct and indirect effects acting in the same direction. Due to its floral display, Hedysarum exerted a direct magnet effect attracting visits to native target plants, especially those made by the honeybee. Indirectly, Hedysarum also increased the visitation rate of native target plants. Due to the competition for resources mediated by its vegetative parts, it decreased floral diversity in the neighbourhoods, which was negatively related to the visitation rate to native target plants. Hedysarum overall also increased the fructification of Leopoldia target plants, even though such an increase was the result of other indirect effects compensating for the observed negative indirect effect mediated by the decrease of floral diversity.

Highlights

Entomophilous non-native plants usually become well integrated into resident plant-pollinator communities, affecting the pollination and reproductive success of native plants [1,2]
Due to the competition for resources mediated by its vegetative parts, it decreased floral diversity in the neighbourhoods, which was negatively related to the visitation rate to native target plants
Our experimental approach has allowed us to disentangle whether these direct and indirect effects are mediated by the floral display or by vegetative interactions associated with the vegetative parts of the non-native Hedysarum (Fig 5)

Summary

Introduction

Entomophilous non-native plants usually become well integrated into resident plant-pollinator communities, affecting the pollination and reproductive success of native plants [1,2]. Non-native plants can indirectly (dashed black arrow in Fig 1) affect the pollination and subsequent reproductive success of a particular native species by altering the composition, abundance and diversity of floral resources in the recipient community [5]. This can be due to their own floral offer or the result of competition for abiotic resources (i.e. nutrients, water and light), allelopathy or the interaction with shared herbivores or pathogens [15,16,17] associated with their vegetative parts (vegetative interactions, hereafter). Separating direct from indirect effects is critical for understanding the mechanisms underlying the impacts of non-native species on recipient communities.

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