Indirect interactions between crops and natural vegetation through flower visitors: the importance of temporal as well as spatial spillover

Lavhelesani D Simba,Stefan H Foord,Elisa Thébault,F.J.Frank Van Veen,Grant S Joseph,Colleen L Seymour

doi:10.1016/j.agee.2017.11.002

Abstract

As the Anthropocene advances, understanding the complex web of interactions between species has become a central theme in the maintenance of biodiversity, ecosystem functions, and agricultural systems. Plant-flower visitor networks yield insights into how natural vegetation supports crop pollination. Although crops themselves also support pollinators, the importance of spillover of flower-visiting pollinators from natural vegetation into croplands is increasingly appreciated. Natural vegetation not only provides forage and nesting sites, but can also support crop flower visitors when the crop is not flowering. We evaluated indirect effects between mango (the dominant tropical fruit crop globally) and wild plant species in neighbouring vegetation, and the factors determining these indirect effects, by constructing flower visitor networks. We constructed these networks for transects that included mango fields and neighbouring natural vegetation in north-eastern South Africa. Surveys were conducted before, during and after mango flowering, to allow evaluation of the importance of pollinator support when the crop was not in flower. Network analysis showed that potential indirect effects of other plant species on mango increased with flower abundance of those species, although this increase was less marked for species growing in natural vegetation. The cumulative (total, i.e. indirect effects summed) effect of natural vegetation on mango flower visitation was greater both during mango flowering and when it was not flowering. This is likely because of the greater plant diversity in natural systems, and because the combination of these species provided flowers over a protracted period. These positive indirect effects among plants flowering over extended periods of time have to date rarely been considered in crop pollination studies. Given the rapid expansion of high-intensity, high-yield monoculture plantings, such effects warrant further investigation.

Highlights

Ecological systems are composed of a host of interacting species and individuals
7 species were exotic weeds found in mango fields, 20 species were in natural vegetation and 11 species were found in both habitats (Table S1)
The mean indirect effect on mango of plant species flowering when mango was not in flower was less than that of plants flowering at the same time as mango (0.011 ± 0.001 and 0.0230 ± 0.006)

Summary

Introduction

Ecological systems are composed of a host of interacting species and individuals. The interactions between these role-players influence the organisms involved, but ecosystem functioning, as they combine to form complex networks at a range of scales (Pocock et al, 2016). As the Anthropocene advances, indirect interactions (that is, the effects of one species on another, mediated by a third species) via pollination of terrestrial plants emerges as key to maintenance of biodiversity, ecosystem function, and agricultural production (Pocock et al, 2016; Sauve et al, 2016; Sotomayor and Lortie, 2015). This is because perturbations can have unforeseen consequences for a number of species via shared resources. Rare plant species may share pollinators with alien invasive species (Carvalheiro et al, 2008), and such knowledge can allow management to mitigate for the removal of alien species from the system while ensuring continued pollination of rare species

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Conclusion