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.

1. More than half of the world's population lives in urban areas, a proportion that is expected to increase. Even if urbanisation is widely regarded as a major threat to global biodiversity, recent research highlighted the potential ecological importance of cities for pollinators. Key determinants of cities' ability to sustain pollinators are the presence of green areas and the connectivity between them.However, also temperature is expected to be of primary importance for pollinator activities.2. Here, we aimed at disentangling the effects of temperature, open habitat cover, and distance from the city centre on wild bee communities in the city of Rome (Italy). We selected 36 sites along two statistically independent gradients of temperature and open habitat cover, and we sampled wild bee communities using pan-traps for 4 months. Then, we measured functional traits of wild bee species, that is, body size, social behaviour, nesting strategy, and diet breadth.3. Temperature emerged as the main driver of wild bee communities, with communities richer in species and individuals at warmer temperatures. We found little species replacement between cold and warm sites. In addition, with increasing temperatures, bee communities were dominated by polylectic and small-bodied species.4. Here, we showed that in a highly urbanised environment, temperature shapes pollinator communities irrespective of other landscape metrics. Even if warming seemed beneficial for urban pollinator abundance and richness, it might strongly homogenise bee communities by selecting for those traits that make species more easily adaptable.

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.

Aim Climate warming and increasing human disturbance are expected to promote non‐native plant invasions in mountain ecosystems. Although biological invasions are also expected to be modulated by biotic interactions, it is still not clear how invertebrate herbivores can affect plant invasion dynamics. Using a large manipulative experiment, we aimed at testing: (1) the effect of soil disturbance and elevation on native and non‐native plant communities, and (2) the effect of plant‐herbivore interactions, nitrogen deposition, and elevation in driving plant establishment after soil disturbance. Location European Alps, NE Italy. Taxon Vascular plants. Methods We selected remote, uninvaded dry semi‐natural grasslands along the core elevational range of non‐native plants in the European Alps (c. 100–1300 m) and manipulated soil disturbance, nitrogen deposition, and invertebrate herbivory. Then, we followed the natural establishment under real field conditions of both native and non‐native plants over one growing season. We used generalized mixed‐effects models to test the effects of the experimental treatments. Results Native and non‐native species showed contrasting responses to soil disturbance and elevation. Low elevations and disturbance promoted non‐native success, while affecting native species diversity negatively. Two‐thirds of the experimental sites acquired novel non‐natives after disturbance. Most of the observed non‐natives were not present in the surrounding vegetation as mature plants, indicating that propagules were able to reach even remote natural areas. While current N deposition levels did not affect plant establishment, we found that after disturbance invertebrate herbivory might play an important role in facilitating non‐native invasions by reducing native cover. Main conclusions Our findings show that highly resistant ecosystems such as continuous grasslands can be easily invaded once the resident vegetation has been removed, and that natural herbivory pressure from invertebrates might amplify the negative effects of disturbance on resident native species irrespective of elevation. Together, these results indicate increasing risks of future plant invasions on mountains under global change.

As predator and parasitoid insects depend on multiple resources for adult feeding and reproduction, environmental heterogeneity (EH) is expected to be a key driver of their species diversity. In temperate regions, the benefits of EH are expected to vary across spatial scales and seasons, depending on species life‐history traits and temporal fluctuations in resources. We tested the importance of EH at multiple spatial scales on diversity and abundance of predator and parasitoid insects, and whether its effects changed across seasons. Insect sampling was carried out in highly fragmented landscapes in a Mediterranean region (Tuscany, Central Italy). We selected 18 semi‐natural patches, embedded in an intensive agricultural matrix. For each patch, EH was measured at three spatial scales (micro, patch, and landscape). Five groups of predator and parasitoid insects were sampled 16 times with pan traps between March and November, 2012. EH at the landscape scale positively influenced the diversity of predator and parasitoid insects, while the effects at smaller spatial scales were less evident. The strength and the direction of EH˗diversity relationship changed between groups and across seasons, indicating that the mechanisms by which EH affects predators and parasitoids are various and complex. Conservation strategies aimed at maximising the diversity of predators and parasitoids should focus more on increasing EH at the landscape scale than at the local scale.

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.

1. Spotted wing drosophila (SWD; Drosophila suzukii Matsumura, 1931) is a polyphagous invasive crop pest native of Southeast Asia able to attack a wide array of host plant species in both cultivated and natural habitats. SWD is now widespread in several mountain regions, but it is still unclear how the species moves to different elevations across the seasons, and how this depends on environmental conditions and food resources.2. The temporal dynamics of several SWD populations were studied along elevational gradients in the Alps using a synchrony analysis. Twelve transects were selected, covering an overall elevational gradient of 2100 m. SWD abundance was monitored every 2 weeks during the growing season (from June to November 2015) when cultivated and wild hosts are potentially susceptible (i.e. fruits are ripe).3. Spotted wing drosophila were widely distributed along all the tested elevations, revealing synchrony in population dynamics across ranges in elevation and geographic distance. Synchronised populations were observed at distances of up to 100 km at sites with similar temperatures. The high dispersal potential of the pest together with the seasonal variation in temperature are likely to be the dominant mechanisms causing the observed spatial synchrony. A factor that seemed to reduce synchrony is the large concentration of host plants (i.e. crop) in lowland agricultural landscapes.4. The spatial synchrony in pest abundance at large spatial scale indicates that the risk of SWD outbreaks is highly dependent on drivers beyond the control of traditional field‐scale management. These findings could help in developing monitoring and predictive models of SWD population dynamics.