Native and exotic plants play different roles in urban pollination networks across seasons

Abstract

Urban areas often host exotic plant species, whether managed or spontaneous. These plants are suspected of affecting pollinator diversity and the structure of pollination networks. However, in dense cityscapes, exotic plants also provide additional flower resources during periods of scarcity, and the consequences for the seasonal dynamics of networks still need to be investigated. For two consecutive years, we monitored monthly plant–pollinator networks in 12 green spaces in Paris, France. We focused on seasonal variations in the availability and attractiveness of flower resources, comparing native and exotic plants at both the species and community levels. We also considered their respective contributions to network properties over time (specialization and nestedness). Exotic plants provided more abundant and diverse flower resources than native plants, especially from late summer on. However, native plants received more visits and attracted more pollinator species at the community level; and during certain times of the year at the species level as well. Exotic plants were involved in more generalist interactions, increasingly so over the seasons. In addition, they contributed more to network nestedness than native plants. These results show that exotic plants are major components of plant–pollinator interactions in a dense urban landscape, even though they are less attractive than natives. They constitute a core of generalist interactions that increase nestedness and can participate in the overall stability of the network. However, most exotic species were seldom visited by insects. Pollinator communities may benefit from including more native species when managing urban green spaces.

Effects of urbanization on the structure of plant-flower visitor network at the local and landscape levels in the northern Argentinian Yungas forest

“…This agrees with previous studies where they show a positive relationship between nestedness and the presence of exotics (Stouffer et al, 2014). Exotic plants are generally involved in generalist interactions, and it has been recently found that they can even contribute more than natives to nestedness in networks of urban areas (Zaninotto et al, 2023). Exotic plants can play an important role in increasing the level of nestedness, thus probably increasing the resilience of these communities in urban areas, as they provide resources in moments when native flowers are not flowering.…”

Some like it hot: adaptation to the urban heat island in common dandelion

“…Exotic plant species are characteristically abundant in the urban habitat, either due to their thriving in disturbed habitats 47 or their use as ornamentals in gardens and parks in temperate cities, providing opportunities for dispersal as garden escapees 49 . Exotic plants are a concern as they initially tend to decrease support for native insect biodiversity 50,51 . Naturally occurring species on the other hand, such as dandelions in Europe, provide an important food source for pollen-and nectar-feeding insects in urban meadows 21 .…”

A picky generalist: nesting females of Pseudaugochlora graminea (Halictidae) are highly specialised in an urban area

“…Hence, it is likely to assume that plant replacements performed in the campus using these native species would be highly advantageous to P. graminea females, as well as to other bee species that perform buzz-pollination. Native plant species are more attractive to pollinators at a community level than exotic species (Zaninotto et al 2023) and should, then, be prioritised by city halls in urban afforestation, parks, squares and other green spaces.…”