Influence of urbanisation and plants on the diversity and abundance of aphids and their ladybird and hoverfly predators in domestic gardens

Elise A Rocha,Christopher Burley,Lewis A.D Bleakley,Mark D.E Fellowes,Estevao N.F Souza,Jade L Mott,Gloria Rue-Glutting

doi:10.14411/eje.2018.013

Abstract

Urban gardens can harbour a high diversity of insects, which are critically important components of urban ecosystems. In this work, we investigate the richness and diversity of a major taxon of economic and ecological importance, the aphids (Homoptera: Aphididae), and their main insect predators, the hoverflies (Diptera: Syrphidae) and ladybirds (Coleoptera: Coccinellidae), in urban gardens. We examined how variation in environmental factors associated with urbanisation (garden host plant abundance, garden plant richness, garden size, proportion of impervious surfaces in the surrounding area) directly and indirectly (via prey and predator abundance) influence the local diversity and abundance of aphids, ladybirds, and hoverflies. Sixty-seven domestic gardens located in southern England were surveyed during the peak period of aphid abundance, and the numbers and identity of aphids and their predators were recorded. We observed 45 aphid species (179917 individuals in total), 15 hoverfly species (494 individuals) and 8 ladybird species (173 individuals). We found that aphid species richness and abundance were positively associated with utilised host plant abundance and garden plant species richness. Hoverfly abundance was positively correlated with garden plant richness. The abundance of ladybirds was positively correlated with aphid abundance and garden plant species richness, and negatively associated to the proportion of impervious surfaces in the surrounding environment. The difference in responses between the two major taxa of aphid predators may reflect differences in their behaviour and natural history. Our results indicate that overall increases in urban land cover are not favourable for ladybirds as a group, and that fine scale habitat variables that are determined by garden owners have the potential to greatly affect the general diversity of aphids and their main predators.

Highlights

Urbanisation is perhaps the most extreme form of widespread anthropogenic habitat modification
We ask how local and fine-scale environmental factors affect the diversity of aphids and their primary predators in urban gardens. Investigating both trophic groups at the same time may provide insights into which group may be more sensitive to urbanisation and its consequences. To address this knowledge gap, we investigate how variation in environmental factors are directly and indirectly associated with the local diversity and abundance of aphids, ladybirds, and hoverflies
We found that aphid species richness and abundance were positively associated with utilised host plant abundance and garden plant species diversity, both traits of gardens largely determined by the homeowner

Summary

Introduction

Urbanisation is perhaps the most extreme form of widespread anthropogenic habitat modification. The magnitude of the effects of urbanisation depends to a marked degree on the composition, amount, and management of green spaces in cities (Marzluff & Ewing, 2001; Loram et al, 2007). This is because urban green spaces can mitigate the detrimental impacts of urbanisation by providing ecosystem services (e.g. nutrient cycling, rainwater drainage) and serving as refuges for plant and animal species (Goddard et al, 2010; Hennig & Ghazoul, 2012). Domestic gardens are a major and important component of green spaces in urbanised areas (Smith et al, 2006).

Methods

Results

Conclusion