Urbanization drives an early spring for plants but not for pollinatorsSubmitted by editor on 4 December 2020.Get the paper!
The sharp increase of urban areas and the associated human population in the last century has put growing pressure on native animal and plant species, as they are threatened by habitat destruction and fragmentation, pollution and changes in climatic conditions such as increased temperatures (urban heat island effect).
In this study we evaluated how the phenology of plant communities and their pollinators responded to different levels of urbanization (Figure 1). More precisely, we assessed whether the plant flowering period and the foraging activity period of wild bees and hoverflies were altered by increasing urbanization, and whether they responded in a similar way or whether there was a possibility for phenological uncoupling. To reduce the variability among study sites, we collaborated with the Parks and Gardens Services of the metropolitan area of Lille (France) to find flowering meadows that were homogeneously managed across the gradient using a standardized seed mix including native herbaceous plant species (Figure 2).
Figure 1. Researchers prepare coloured pan traps to capture pollinators in an urban site in early April (A). By mid- to late-June most plants have already bloomed and flower resources are becoming scarce (B).
Figure 2. The Park and Gardens Services of the Métropole Européenne de Lille manages several meadows in urban and peri-urban habitats to favour biodiversity. Even small areas can be very effective due to the large variety of native plants that flower at different time periods.
We found a high diversity of pollinators at all sites (Figure 3), with no temporal variation in species richness across the gradient. Similarly, we did not find significant temporal shifts in pollinator abundance at different urbanization levels. However, we recorded a strong effect of urbanization on plant flowering phenology. The flowering peak occurred up to four weeks earlier in areas at high urbanization than in areas at low urbanization, and a similar pattern was found for plant species richness. These results show a potential mismatch between plant flowering phenology and pollinator activity in relation to increased urbanization. Moreover, our results highlight the importance of green spaces for biodiversity conservation in urban areas: a management focused on providing plants with flowering times that match the different periods of activity of pollinators and support the pollinator diversity, based on the level of urbanization, could reduce negative consequences on both partners of the plant-pollinator interaction.
We are currently investigating how the differential responses of plant and pollinator phenology across the gradient affect the structure of plant-pollinator interaction networks and the role of species therein.
Figure 3. Urban meadows managed with native flowering plants can host a wide diversity of pollinators, including several species of wild bees and hoverflies. Here we see a bumblebee (Bombus lapidarius) seeking nectar on a knapweed (Centaurea jacea, A) and a hoverfly (Eristalis tenax, mimicking the colours of a honeybee) eating pollen on an oxeye daisy (Leucanthemum vulgare, B).
Alessandro Fisogni, Nina Hautekèete, Yves Piquot, Marion Brun, Cédric Vanappelghem, Denis Michez and François Massol
CLIMIBIO Project: @CPER_CLIMIBIO
EEP Laboratory: @Evo_Eco_Paleo
Alessandro Fisogni: @nowehere_23