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

The wild bees (Hymenoptera, Apoidea, Anthophila) of the urban nature reserves of Rome (Italy, Latium): a preliminary survey

Background

Urbanisation is a global phenomenon responsible for negative processes in natural ecosystems, such as degradation, loss of habitat and fragmentation. Large urban green areas could, however, represent shelter for animal species, promoting biodiversity conservation. Urban green spaces can also provide useful habitats for threatened species. Wild bees are amongst the most important and efficient pollinating insects and play an indispensable role in ecosystem functioning. Approximately half of the European wild bee species have been reported from Italy, making it a biodiversity hotspot for this group of insects. Many studies have been conducted on pollinating insects in recent years, but few data and incomplete knowledge on wild bee faunas in strictly urban environments exist. Georeferenced faunal data would be important for conservation efforts and understanding the effects that large cities such as Rome may have on the diversity of wild bee communities.

New information

This work focused on the diversity of wild bees in nature reserves belonging to the RomaNatura network within the urban area of Rome, Italy. A total of 208 wild bee species belonging to 36 genera and six families were identified. Amongst the species surveyed, one species was classified as Endangered (EN) and seven species were classified as Near Threatened (NT) by the European Red List of wild bees. Twenty-four species are new reports for the urban area of Rome. Sampling took place from April to September 2022. The most represented family in terms of abundance was Halictidae, accounting for 36% of all bees collected, followed by Apidae (24% of samples), Andrenidae (17% of samples), Megachilidae (15% of samples), Colletidae (7% of samples) and Melittidae (1% of samples). The Megachilidae family was the richest in terms of the number of species, accounting for 25% of the total species sampled. This research aimed to provide a set of standardised and georeferenced wild bee occurrences that constitute the baseline for any faunistic, ecological and conservation activity of Rome's nature reserves. In addition, the research aims to demonstrate the importance of large urban green areas in one of the largest European cities as biodiversity reservoirs for wild bees.

Exotic and native plants play equally important roles in supporting and structuring plant-hummingbird networks within urban green spaces

Background

Urban gardens, despite their transformed nature, serve as invaluable microcosms for a quantitative examination of floral resource provision to urban pollinators, considering the plant's origin. Thus, knowledge has increased, emphasizing the importance of these green areas for hosting and conserving pollinator communities. However, there is a significant knowledge gap concerning the changing availability of these native and exotic floral resources over time and their impact on structuring interaction networks with specific pollinators.

Methods

Over a year-long period, monthly surveys were conducted to record both native and exotic plant species visited by hummingbirds in an urban garden at Tlaxcala, Mexico. Flower visits were recorded, and the total flowers on each plant visited were tallied. Additionally, all observed hummingbirds were recorded during the transect walks, regardless of plant visits, to determine hummingbird abundance. The interactions were summarized using matrices, and network descriptors like connectance, specializacion, nestedness, and modularity were computed. Plant and hummingbird species in the core and periphery of the network were also identified. Lastly, simulations were performed to assess the network's resilience to the extinction of highly connected native and exotic plant species, including those previously situated in the network's core.

Results

We recorded 4,674 interactions between 28 plant species, and eight hummingbird species. The majority of plants showed an ornithophilic syndrome, with 20 species considered exotic. Despite asynchronous flowering, there was overlap observed across different plant species throughout the year. Exotic plants like Jacaranda mimosifolia and Nicotiana glauca produced more flowers annually than native species. The abundance of hummingbirds varied throughout the study, with Saucerottia berillyna being the most abundant species. The plant-hummingbird network displayed high connectance, indicating generalization in their interaction. Significant nestedness was observed, mainly influenced by exotic plant species. The core of the network was enriched with exotic plants, while Basilinna leucotis and Cynanthus latirostris played central roles among hummingbirds. Network resilience to species extinction remained generally high.

Conclusions

Our findings provide valuable insights into the dynamics and structure of plant-hummingbird interactions in urban gardens, emphasizing the influence of exotic plant species and the network's resilience to perturbations. Understanding and managing the impact of exotic plants on such networks is crucial for the conservation and sustainable functioning of urban ecosystems.