Urbanization drives an early spring for plants but not for pollinators

Abstract

Urbanization is one of the major threats to wild plants and pollinators, and its global increase demands a better understanding of the mechanism driving its negative impact. Urban warming and altered local environmental conditions have the potential to affect the timing of flowering and of pollinator activity. While previous evidence has shown that plant phenology tends to advance in urban areas, little is known about its effects on pollinator phenology. In this study we simultaneously assessed the response of the timing of flowering of native plants and of the flight period of wild pollinators to increased urbanization. We collected data from 12 sites along an urbanization gradient in northern France, a region under strong anthropogenic pressure. Overall, we recorded more than 70 plant species, and we sampled more than 4300 wild bees and hoverflies belonging to 154 species. Plant flowering showed a strong response to urbanization at the community level with a striking advancement of the flowering peak in sites at high urbanization. On the contrary, pollinator communities did not show any clear shift of their flight phenology along the gradient, neither regarding abundance nor diversity. Our results indicate that phenologies of plant and pollinator communities can respond differently along the same urbanization gradient. These asymmetric responses can drive modifications in the structure of plant–pollinator networks, and potentially negatively affect the fitness of both mutualistic partners.

Supporting Bees in Cities: How Bees Are Influenced by Local and Landscape Features

“…Microclimates, or local climatic conditions within habitats, can vary across urban environments and even within individual habitat patches depending on the biotic and abiotic qualities of a space [ 13 , 74 , 75 ]. Vegetation type and cover along with background environmental warming are two such characteristics that can influence local microclimate [ 76 ].…”

Valuing the Role of Time in Urban Ecology

“…The cascading effects of this asynchrony on plantanimal interactions are largely uncharacterized. In a rare example along these lines, Fisogni et al (2020) recently observed that urbanization advanced the timing of flowering in France, but not pollinator flight, potentially leading to disrupted pollination in cities. In another example, ecological theory predicts that higher trophic levels may become less synchronized due to the urban heat island effect, disrupting ecosystem services, such as biological pest control.…”

Climate drivers of adult insect activity are conditioned by life history traits

“…Less is known about insects' phenological response to urbanization. The emergence of some insect species appears to be advancing in urbanized areas (Diamond et al, 2015;Chick et al, 2019), but other studies have found no change in phenology across urbanization gradients, despite phenological advances in co-occurring plant species (Seress et al, 2018;Fisogni et al, 2020). The interaction between urbanization and regional temperature can be an important driver of spatial phenology patterns, as urbanization appears to advance plant phenology in cold areas but causes delays in warm areas (Li et al, 2019).…”