Functional homogenization of flower visitor communities with urbanization.

Nicolas Deguines,Colin Fontaine,Romain Julliard,Mathieu De Flores

doi:10.1002/ece3.2009

Nicolas Deguines, Colin Fontaine + Show 2 more

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https://doi.org/10.1002/ece3.2009

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Abstract

Land‐use intensification and resulting habitat loss are put forward as the main causes of flower visitor decline. However, the impact of urbanization, the prime driver of land‐use intensification in Europe, is poorly studied. In particular, our understanding of whether and how it affects the composition and functioning of flower visitor assemblages is scant, yet required to cope with increasing urbanization worldwide. Here, we use a nation‐wide dataset of plant‐flower visitor (Coleoptera, Diptera, Hymenoptera, Lepidoptera) interactions sampled by citizen scientists following a standardized protocol to assess macroecological changes in richness and composition of flower visitor communities with urbanization. We measured the community composition by quantifying the relative occurrence of generalist and specialist flower visitors based on their specialisation on flowering plant families. We show that urbanization is associated with reduced flower visitor richness and a shift in community composition toward generalist insects, indicating a modification of the functional composition of communities. These results suggest that urbanization affects not only the richness of flower visitor assemblages but may also cause their large‐scale functional homogenization. Future research should focus on designing measures to reconcile urban development with flower visitor conservation.

Highlights

Biodiversity decline continues (Butchart et al 2010) with likely implications for the functioning of ecosystems (Cardinale et al 2012)
We found no evidence of spatial autocorrelation in the residuals of our models using both graphical assessment with spline correlograms (Zuur et al 2009) and Moran’s I index
We found a significant negative effect of the proportion of urban areas on Community Specialisation Index (CSI), and this effect was independent of the plant family as shown by the absence of significant interaction between the proportion of urban areas and plant family (Table 3, Fig. 3C)

Summary

Introduction

Biodiversity decline continues (Butchart et al 2010) with likely implications for the functioning of ecosystems (Cardinale et al 2012). Reports from several countries indicated that insect flower visitors, including many pollinators which provide both key ecosystem function and services (Dupont and Olesen 2009; Vanbergen and the Insect Pollinators Initiative 2013), experienced downward historical shifts [e.g. wild bees and hoverflies (Biesmeijer et al 2006), and butterflies (Thomas et al 2004)]. Habitat loss resulting from land-use intensification was proposed as the main cause of flower visitor decline (Vanbergen and the Insect Pollinators Initiative 2013) as both the intensification of agricultural lands and practices (Kennedy et al 2013) and urbanization (McKinney 2008; Bates et al 2011) were found to decrease their richness. Reports of changes in flower visitor diversity often rely on richness alone (Winfree et al 2011). Carvalheiro et al (2013) found that the similarity of bee, hoverfly or butterfly assemblages increased between 1950 and 2009 in some European countries, revealing a taxonomic homogenization that decreases the overall diversity

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