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Landscapes are becoming increasingly urbanized, causing loss and fragmentation of natural habitats, with potentially negative effects on biodiversity. Insects are among the organisms with the largest diversity in urbanized environments. Here, we sampled predator (Ampulicidae, Sphecidae and Crabronidae) and parasitoid (Tachinidae) flower-visiting insects in 36 sites in the city of Rome (Italy). Although the diversity of herbivorous insects in urban areas mostly depends on the availability of flowering plants and nesting sites, predators and parasitoids generally require a larger number of resources during their life cycle, and are expected to be particularly influenced by urbanization. As flower-visitors can easily move between habitat patches, the effect of urbanization was tested at multiple spatial scales (local, landscape and sub-regional). We found that urbanization influenced predator and parasitoid flower-visitors at all three spatial scales. At the local scale, streets and buildings negatively influenced evenness of predators and species richness and abundance of parasitoids probably acting as dispersal barrier. At the landscape scale, higher percentage of urban decreased predator abundance, while increasing their evenness, suggesting an increase in generalist and highly mobile species. Area and compactness (i.e. Contiguity index) of urban green interactively influenced predator communities, whereas evenness of parasitoids increased with increasing Contiguity index. At the sub-regional scale, species richness and abundance of predators increased with increasing distance from the city center. Compared to previous studies testing the effect of urbanization, we found little variation in species richness, abundance and evenness along our urbanization gradient. The current insect fauna has been probably selected for its tolerance to habitat loss and fragmentation, being the result of the intensive anthropogenic alteration occurred in the area in the last centuries. Conservation strategies aimed at predator and parasitoid flying insects have to take in account variables at multiple spatial-scales, as well as the complementarity of resources across the landscape.

Elevational gradients are characterized by strong abiotic variation within small geographical distances and provide a powerful tool to evaluate community response to variation in climatic and other environmental factors. We explored how temperature and habitat diversity shape the diversity of holometabolous predator and parasitoid insects along temperate elevational gradients in the European Alps. We surveyed insect communities along 12 elevational transects that were selected to separate effects of temperature from those of habitat diversity. Pitfall traps and pan traps were placed every 100 m of elevation increment along the transects ranging from 120 to 2200 m a.s.l. Sampling took place once a month from June to September 2015. Four groups characterized by having at least one life stage behaving as predator or parasitoid were examined: tachinids (Diptera), hoverflies (Diptera), sphecids (Hymenoptera) and ground beetles (Coleoptera). Species richness and evenness changed with elevation, but the shape and direction of the elevation–diversity patterns varied between groups. The effect of temperature on species richness was positive for all groups except for hoverflies. Habitat diversity did not affect species richness, while it modulated the evenness of most groups. Often, elevational patterns of species richness and evenness were contrasting. Our study indicates that natural enemies characterized by diverse ecological requirements can be differentially affected by temperature and habitat diversity across the same elevational gradients. As climate warming is predicted to increase mean annual temperatures and exacerbate weather variability, it is also expected to strongly influence natural enemies and their ability to regulate herbivore populations.

Aim To explore how a highly invasive plant species (Buddleja davidii Franch.), managed honeybees and flower diversity affected plant–flower visitor interactions over the whole elevational range distribution of the exotic plant. Location Italian Alps. Methods We selected nine pairs of sites (one invaded and one non‐invaded by B. davidii) across gradients in honeybee abundance and diversity of flower resources. We observed plant–flower visitor interactions every three weeks, for a total of five surveys covering the full flowering season of B. davidii (June–August). We tested how B. davidii, honeybee abundance and flowering plant diversity affected network robustness, overlap in flower resource use of wild flower visitors with honeybees and flower visitor specialization. We also tested for an interaction between B. davidii presence and honeybee abundance, and tested whether the effects of the two variables changed among insect orders. Results Buddleja davidii and honeybees had contrasting effects on network robustness and on several species‐level metrics. Network robustness increased with increasing honeybee abundance and flower diversity. Increasing honeybee abundance generally increased specialization of lepidopterans and dipterans that tended to switch to less visited plant species, possibly in order to avoid competition. Specialization of flower visitors declined in sites invaded by B. davidii, indicating that the invasive plant attracted pollinators, which in turn also visited co‐occurring species in the neighbourhood. Main conclusions Although increasing honeybee abundance was associated with higher network stability, it also modified plant–flower visitor interactions by forcing species to shift their diet irrespective of floral diversity. The effect was particularly strong for non‐bee flower visitors. The consequences of these changes in plant–flower visitor interactions for the reproductive success of flowering plants are still largely unknown.

Questions How does small‐scale soil disturbance influence establishment dynamics of native and exotic species along roadsides? Does soil disturbance provide potential opportunities to exotic invasions along elevational gradients? Does the established plant community after disturbance reflect the surrounding vegetation? Location Prealps, Italy. Methods To disentangle the role of elevation and soil disturbance in promoting exotic invasions, we performed a manipulative experiment along 12 roads spanning an elevational gradient of ca. 1,200 m. Additionally, we sampled species richness of native and exotic plants in the surroundings of the experimental plots. Results Soil disturbance reduced species richness of native plants, total plant biomass and vegetation cover compared to the undisturbed plots. The decrease in species richness of natives and plant biomass was stronger at higher than lower elevations, suggesting higher colonization opportunities for exotics. However, exotic species richness did not increase with disturbance, probably due to a low propagule and colonization pressure. We observed strong species replacement between control and disturbed plots, indicating that plant communities established after disturbance were not a subset of species communities already occurring in the surrounding vegetation. Conclusions With increasing elevation, disturbance had a stronger negative effect on native than on exotic species. Higher elevations, hitherto considered to have low invasibility, may provide new potential colonization opportunities for exotics but only if disturbance is coupled with an increased propagule pressure. Disturbance along roadsides promoted the establishment of species that did not occur in the surrounding vegetation. A manipulative experiment was performed in order to disentangle the role of elevation and soil disturbance in promoting plant colonization along roadsides. Soil disturbance reduced the number of natives, plant biomass and cover, with the effects being stronger at high elevations. These areas may provide new opportunities for species invasions, should temperature and anthropic activities increase propagule pressure in the future.