Dr. Marco Moretti

Land-use changes, driven by agricultural intensification and urbanization, are major contributors to biodiversity loss, altering habitats and reducing available resources. These changes impact species’ foraging strategies, particularly in human-modified ecosystems. While dietary shifts due to land-use changes have been well-studied in vertebrates, similar research in invertebrates, such as wild bees, remains limited. The present data paper provides a comprehensive dataset on the pollen collected from urban and rural populations of two bumblebee species (Bombus lapidarius and B. pascuorum) in Switzerland, examining pollen composition, nutrient content, and diet breadth. Additionally, by analyzing pollen from both body and leg-baskets, the dataset also offers a comprehensive overview of plant-bumblebee interactions. The data help understand plant-bumblebee interactions, pollination services, nutritional supply to larvae, and the impact of land-use changes on these processes. Furthermore, the dataset can be integrated with existing plant trait data to explore the effects of non-native species and other ecological factors on bumblebee foraging and nutrition in anthropogenically modified landscapes.

Understanding how land use affects temporal stability is crucial to preserve biodiversity and ecosystem functions. Yet, the mechanistic links between land-use intensity and stability-driving mechanisms remain unclear, with functional traits likely playing a key role. Using 13 years of data from 300 sites in Germany, we tested whether and how trait-based community features mediate the effect of land-use intensity on acknowledged stability drivers (compensatory dynamics, portfolio effect, and dominant species variability), within and across plant and arthropod communities. Trait-based plant features, especially the prevalence of acquisitive strategies along the leaf-economics spectrum, were the main land-use intensity mediators within and across taxonomic and trophic levels, consistently influencing dominant species variability. Functional diversity also mediated land-use intensity effects but played a lesser role. Our analysis discloses trait-based community features as key mediators of land-use effects on stability drivers, emphasizing the need to consider multi-trophic functional interactions to better understand complex ecosystem dynamics.

Urban biodiversity and ecosystem services depend on the quality, quantity, and connectivity of urban green areas (UGAs), which are crucial for enhancing urban livability and resilience. However, assessing these connectivity metrics in urban landscapes often suffers from outdated land cover classifications and insufficient spatial resolution. Spectral data from Earth Observation, though promising, remains underutilized in analyzing UGAs' connectivity. This study tests the impact of dataset choices on UGAs' connectivity assessment, comparing land cover classification (Urban Atlas) and spectral data (Normalized Difference Vegetation Index, NDVI). Conducted in seven European cities, the analysis included 219 UGAs of varying sizes and connectivity levels, using three connectivity metrics (size, proximity index, and surrounding green area) at different spatial scales. The results showed substantial disparities in connectivity metrics, especially at finer scales and shorter distances. These differences are more pronounced in cities with contiguous UGAs, where Urban Atlas faces challenges related to typology issues and minimum mapping units. Overall, spectral data provides a more comprehensive and standardized evaluation of UGAs' connectivity, reducing reliance on local typology classifications. Consequently, we advocate for integrating spectral data into UGAs’ connectivity analysis to advance urban biodiversity and ecosystem services research. This integration offers a comprehensive and standardized framework for guiding urban planning and management practices.

1. Urban ecosystems are formed by pronounced socio-ecological gradients, which are distinct from other ecosystems and can simultaneously filter and promote taxa, ultimately affecting their interactions. However, the strength of the effect of filtering and facilitation across the different trophic levels could vary among biotic and abiotic factors.
2. Here, we investigate the effects of habitat amount, temperature and host-enemy biotic interactions in shaping communities of cavity-nesting bees and wasps and their natural enemies. We installed trap-nests in 80 sites distributed along urban intensity gradients in five European cities (Antwerp, Paris, Poznan, Tartu and Zurich). We quantified the species richness and abundance of hosts and their natural enemies, as well as two performance traits (survival and parasitism) and two lifehistory traits (sex ratio and number of offspring per nest for the hosts). We analysed the importance of the abiotic and biotic variables using generalised linear models and multi-model inference.
3. We found that habitat amount was the main driver of multiple host responses, with larger habitat amounts resulting in higher species richness and abundance for hosts and natural enemies, as well as a larger probability of survival and a larger number of brood cells for hosts.
4. Local resources proxies shaped both bees and wasps and indicate different uses of existing vegetation between bees and wasps. Temperature proxies had a minor role in shaping host and natural enemies.
5. Biotic interactions were a main driver of host and enemy community structure, with natural enemies being strongly affected by host availability, that is, with direct density-dependence between hosts and their natural enemies. 6. Overall, our study highlights the importance of habitat amount and temperature in shaping urban food webs, as well as on biotic interactions through direct effects on hosts responses and the subsequent consequences for their natural enemies. As cities prepare to tackle the consequences of global change, strategies that make it possible to maintain habitat and mitigate urban overheating emerge as a key urban adaptation for biodiversity conservation.

In cities, green areas are essential for biodiversity conservation, with land cover heterogeneity being a decisive factor. Yet, as heterogeneity increases for a given green area, the patch size of land covers automatically decreases, as the area available for individual species, especially habitat specialist species. This relationship, known as the area-heterogeneity trade-off, is expected to lead to a unimodal relationship between species richness and land cover heterogeneity, and contrasted effects between species according to their level of urban avoidance.
We investigated the potential consequences of this trade-off on birds in green areas selected along an urban intensity gradient in six European cities. Using a European database on bird occurrences in nesting habitats, we defined a continuous gradient of urban avian avoidance.
We confirmed the marked area-heterogeneity trade-off in urban green areas but found no effect of land cover heterogeneity on total avian richness at green area level. However, both land cover heterogeneity and patch size were positively associated with richness of urban avoider species, indicating that urban avoiders fared better in green areas with large and heterogeneous patches. Total richness was also higher in green areas surrounded by an urban matrix composed of a variety of land covers.
To protect urban bird avoiders, which are most at risk in cities, green area managers and urban planners should thus be aware that land cover heterogeneity is not a panacea if patch sizes are too small. To conserve avian richness, we stress the importance of maintaining large vegetated areas as well as heterogeneity in land covers within the urban matrix.

Decades of research on multifunctional Green Infrastructure (GI) has yet to translate into holistic implementation in the built environment. This oversight stems from assumptions that many ecosystem services occur passively and thus potential synergies are overlooked during planning and design. This study offers specific guidance for coordinating GI planning, design, and construction by examining the current state of academic literature on these aspects. It identifies 15 GI elements (e.g., green roofs) and 15 objectives (e.g., biodiversity) to collectively consider before implementation. The literature tends to isolate discussions of “engineered” GI elements with water-related objectives, while more “natural” GI are linked to biodiversity and human well-being. Coordinating across GI objectives and elements remains imperative, but evaluating too many options risks a paradox of choice. This study recommends short-term adherence to principles of adaptive design and, in the long-term, reemphasizes multifunctionality assessments, inter and transdisciplinary collaboration, and political will.

Robust, quantitative understanding of the diverse ecological needs of species is needed to inform effective biodiversity conservation, now and in the future, but is lacking for most species. The advent of "big data" in ecology presents unprecedented opportunities to fill this gap and to disentangle the diverse drivers of biodiversity. Variable and model selection in sparse (small sample sizes for most species), high-dimensional (large pool of candidate predictors) problems is, however, non-trivial. Here, we employ cross-validated Bayesian projection predictive variable selection and shrinkage priors to identify, from a list of 70 ecological and biophysical candidate predictor variables, the minimal subset that best predicts the habitat preferences and distributions of 103 species of amphibians, birds, butterflies, dragonflies, and grasshoppers using the city of Zurich, Switzerland, as a case study. We contrast the predictive performance and ecological inference of models fit with the full set of predictors using shrinkage priors (exhaustive models) to models fit with a limited number of predictors obtained by compiling predictors from the full list of predictors using weakly informative priors (selective models). We show that exhaustive models excel in predictive performance, albeit at the cost of greater model complexity compared to selective models. Results from the selective models reveal the importance of access to aquatic habitat for a wide range of taxa, relative to other drivers such as urbanisation, vegetation and environmental hazards. These results are complemented by more nuanced insights from the exhaustive models into the importance of specific types of aquatic habitat (ponds, lakes, streams) and vegetation (herb, shrub, canopy cover) for the distribution of urban biodiversity, as well as the different spatial scales at which drivers are of predictive relevance. Our findings demonstrate the potential of shrinkage-based Bayesian variable selection to leverage big ecological data for species distribution modelling, and contribute to the development of concrete guidelines for urban planning and infrastructure design that account for biodiversity conservation.

The emergence of novel ecosystems, characterized by shifts in species composition and interactions, abiotic conditions and altered ecosystem functioning, is a major and inevitable challenge to contemporary ecosystem management. This study examines the ecological implications of Trachycarpus fortunei, a non-native evergreen palm, currently involved in a biome shift from deciduous temperate forest to evergreen laurophyllous forest in the Southern European Alps. Specifically, we investigated the effects of T. fortunei encroachment in peri-urban forests on flying and ground-dwelling arthropod communities as well as on leaf-litter decomposition. We found that the presence of T. fortunei altered arthropod community composition, mostly by reducing the number of herbivore species. This effect was likely driven by the lower quality of palm leaves as a food source compared to deciduous, dicotyledonous tree leaves and by a lower plant richness in the herb and shrub layer. Furthermore, we observed higher rates of leaf-litter decomposition associated with increasing abundance of young palm trees, which was not explained by predictors commonly associated with litter decomposition (i.e., detritivore abundance, litter depth and air temperature). Hence, the slow decay of palm leaves appears to be counterbalanced by the favourable conditions for litter decomposition within dense palm stands. Overall, our findings indicate that high densities of the non-native palm species (T. fortunei) impacts herbivore arthropod communities in the Southern European Alps, providing first evidence of possible effects on ecosystem functioning of this ongoing biome shift. These outcomes are integral components of the broader process of laurophyllisation in the study region, a phenomenon linked to climate warming and land use change, encompassing both native and non-native species.

Many authors have described ‘urban ecology’ as a subfield of ecology that emerged in the 1990s and has expanded exponentially. We propose to take a step further and analyse the expansion of the ‘urban’ in ecology with a novel quantitative approach, with the aim to better understand the relationship between ecology and the urban. Previous quantitative assessments of the urban in ecology have focused on short to medium time spans (5 to 40 years) and on research coined as ‘urban ecology’, and have rarely considered the content of publications (e.g., vocabulary and topics) using quantitative methods. In this paper, we conduct a bibliometric assessment and an in-depth quantitative textual data analysis of a corpus of 960 articles published from 1922 to 2018 in 10 leading English-language journals in ecology and conservation biology. We address the following questions: (1) When and how have urban environments been integrated into ecological research during the past century? (2) What urban research topics have been investigated in ecology during the same period? (3) How have these research topics changed through time? Our results show that the urban was never entirely absent from publications in ecology. The quantitative analyses highlight three turning points (1970s, 1990s and 2000s) in the relationship between ecology and the urban. Moreover, they help visualize the shift from particularly scattered publications at the beginning of the period to publications characterized by a more homogeneous vocabulary, reflecting the stabilization of a research field focused on the urban in ecology.

Promoting urban green spaces is an effective strategy to increase biodiversity in cities. However, our understanding of how local and landscape factors influence trophic interactions in these urban contexts remains limited. Here, we sampled cavity-nesting bees and wasps and their natural enemies within 85 urban gardens in Zurich (Switzerland) to identify factors associated with the diversity and dissimilarity of antagonistic interactions in these communities. The proportions of built-up area and urban green area at small landscape scales (50 m radius), as well as the management intensity, sun exposure, plant richness and proportion of agricultural land at the landscape scale (250 m radius), were key drivers of interaction diversity. This increased interaction diversity resulted not only from the higher richness of host and natural enemy species, but also from species participating in more interactions. Furthermore, dissimilarity in community structure and interactions across gardens (beta-diversity) were primarily influenced by differences in built-up areas and urban green areas at the landscape scale, as well as by management intensity. Our study offers crucial insights for urban planning and conservation strategies, supporting sustainability goals by helping to understand the factors that shape insect communities and their trophic interactions in urban gardens.

1. Understanding how anthropogenic activities induce changes in the functional traits of arthropod communities is critical to assessing their ecological consequences. However, we largely lack comprehensive assessments of the long-term impact of global-change drivers on the trait composition of arthropod communities across a large number of species and sites. This knowledge gap critically hampers our ability to predict human-driven impacts on communities and ecosystems.
2. Here, we use a dataset of 1.73 million individuals from 877 species to study how four functionally important traits of carabid beetles and spiders (i.e. body size, duration of activity period, tolerance to drought, and dispersal capacity) have changed at the community level across ~40 years in different types of land use and as a consequence of land use changes (that is, urbanisation and loss of woody vegetation) at the landscape scale in Switzerland.
3. The results show that the mean body size in carabid communities declined in all types of land use, with particularly stronger declines in croplands compared to forests. Furthermore, the length of the activity period and the tolerance to drought of spider communities decreased in most land use types. The average body size of carabid communities in landscapes with increased urbanisation in the last ~40 years tended to decrease. However, the length of the activity period, the tolerance to drought, and the dispersal capacity did not change significantly. Furthermore, urbanisation promoted increases in the average dispersal capacities of spider communities. Additionally, urbanisation favoured spider communities with larger body sizes and longer activity periods. The loss of woody areas at the landscape level was associated with trait shifts to carabid communities with larger body sizes, shorter activity periods, higher drought tolerances and strongly decreased dispersal capacities. Decreases in activity periods and dispersal capacities were also found in spider communities.
4. Our study demonstrates that human-induced changes in land use alter key functional traits of carabid and spider communities in the long term. The detected trait shifts in arthropod communities likely have important consequences for their functional roles in ecosystems.

Blue-green infrastructure (BGI), combining semi-natural and engineered elements, offers multifaceted benefits like stormwater management, water purification, heat mitigation, and habitat provision. However, current BGI designs prioritize engineering goals, overlooking its ecological potential. Here we advocate for integrating engineering and ecological objectives into BGI design to enhance performance and biodiversity. Through an interdisciplinary literature review, we emphasize the importance of species diversity, abundance, and ecological processes, to improve engineering performance and resilience, and lower management costs. We emphasize the importance of interdisciplinary collaboration to navigate trade-offs between engineering and ecological objectives, ultimately enabling us to engineer both for and with biodiversity.

Urban gardens have the potential to contribute to urban bee biodiversity. However, studies considering the effects of habitat amount and floral resources on bees using a functional approach, are largely lacking in Latin America, in particular in urban environments, where the potential competitive interactions between honeybees and wild bees deserve further attention. We evaluated how bee abundance and diversity, both taxonomic (richness, evenness) and functional (richness, evenness, and divergence of traits), are related to habitat amount in urban gardens (patch size, green cover in the surroundings), and the abundance and diversity of flowers (taxonomic and functional). We also examined the effect of the abundance of honeybees on urban wild bee communities. We selected 13 gardens within Córdoba city (Argentina) along an urbanization gradient based on vegetation cover, where we surveyed bee-flower interactions. We selected flower (i.e. morphology, color, and phenology) and bee (i.e. morphology, sociality, and diet) traits considered essential to plant-pollinator interactions to estimate flower and bee functional diversity, respectively. Bee taxonomic and functional diversity in urban gardens strongly depended on the floral species evenness, whereas the functional floral diversity and patch size, as well as the habitat amount at the landscape scale, did not significantly affect bee diversity. Moreover, the abundance of honeybees, once controlled by floral species evenness, did not influence the taxonomic structure of wild bee communities. Our results highlight that urban gardens can support functionally diverse bee communities, especially those with evenly distributed flower species.

Cities are socioecological systems that filter and select species, therefore establishing unique species assemblages and biotic interactions. Urban ecosystems can host richer wild bee communities than highly intensified agricultural areas, specifically in resource-rich urban green spaces such as allotments and family gardens. At the same time, urban beekeeping has boomed in many European cities, raising concerns that the fast addition of a large number of managed bees could deplete the existing floral resources, triggering competition between wild bees and honeybees. Here, we studied the interplay between resource availability and the number of honeybees at local and landscape scales and how this relationship influences wild bee diversity. We collected wild bees and honeybees in a pollination experiment using four standardized plant species with distinct floral morphologies. We performed the experiment in 23 urban gardens in the city of Zurich (Switzerland), distributed along gradients of urban and local management intensity, and measured functional traits related to resource use. At each site, we quantified the feeding niche partitioning (calculated as the average distance in the multidimensional trait space) between the wild bee community and the honeybee population. Using multilevel structural equation models (SEM), we tested direct and indirect effects of resource availability, urban beekeeping, and wild bees on the community feeding niche partitioning. We found an increase in feeding niche partitioning with increasing wild bee species richness. Moreover, feeding niche partitioning tended to increase in experimental sites with lower resource availability at the landscape scale, which had lower abundances of honeybees. However, beekeeping intensity at the local and landscape scales did not directly influence community feeding niche partitioning or wild bee species richness. In addition, wild bee species richness was positively influenced by local resource availability, whereas local honeybee abundance was positively affected by landscape resource availability. Overall, these results suggest that direct competition for resources was not a main driver of the wild bee community. Due to the key role of resource availability in maintaining a diverse bee community, our study encourages cities to monitor floral resources to better manage urban beekeeping and help support urban pollinators.

Wild bees are critical for multiple ecosystem functions but are currently threatened. Understanding the determinants of the spatial distribution of wild bee diversity is a major research gap for their conservation. We modeled wild bee α and β taxonomic and functional diversity in Switzerland to uncover countrywide diversity patterns and determine the extent to which they provide complementary information, assess the importance of the different drivers structuring wild bee diversity, identify hotspots of wild bee diversity, and determine the overlap between diversity hotspots and the network of protected areas. We used site-level occurrence and trait data from 547 wild bee species across 3343 plots and calculated community attributes, including taxonomic diversity metrics, community mean trait values, and functional diversity metrics. We modeled their distribution with predictors describing gradients of climate, resource availability (vegetation), and anthropogenic influence (i.e., land-use types and beekeeping intensity). Wild bee diversity changed along gradients of climate and resource availability; high-elevation areas had lower functional and taxonomic α diversity, and xeric areas harbored more diverse bee communities. Functional and taxonomic β diversities diverged from this pattern, with high elevations hosting unique species and trait combinations. The proportion of diversity hotspots included in protected areas depended on the biodiversity facet, but most diversity hotspots occurred in unprotected land. Climate and resource availability gradients drove spatial patterns of wild bee diversity, resulting in lower overall diversity at higher elevations, but simultaneously greater taxonomic and functional uniqueness. This spatial mismatch among distinct biodiversity facets and the degree of overlap with protected areas is a challenge to wild bee conservation, especially in the face of global change, and calls for better integrating unprotected land. The application of spatial predictive models represents a valuable tool to aid the future development of protected areas and achieve wild bee conservation goals.

This paper investigates urban imaginaries conveyed in publications in ecology over the past century. We examine some urban ecologists’ view that urban areas have been disregarded by ecology due to negative views on cities and urbanisation. Inspired by previous work on imaginaries in social and cultural geography and political ecology, and by textual data analysis methods, we adopted a methodological framework that applies both quantitative and qualitative methods in the analysis of a corpus of 960 articles (published 1922-2018) drawn from 10 long-standing international journals in ecology. Our hypothesis is that ecology has embraced an anti-urban imaginary that is manifested in urban invisibility as well as the recurrent expression of negative ideas about cities (constituting an ‘anti-urban bias’). Our results partially confirm this hypothesis. We show that until the 1970s only a few papers were published on cities. We identify nine main themes relating to cities around which ideas about cities have been constructed (threats, pests, refuges, fragmentation, gradients, pollution, homogenisation, planetary urbanisation, and planning) and show how these ideas have been mobilised in the articles since the 1920s. We discuss the way in which these evolving ideas reflect a move from an essentially anti-urban imaginary to a more complex and ambivalent one. This shift coincides with the rise of the idea of planetary urbanisation in ecological publications, increasing recommendations regarding urban planning, and more generally, growing conceptual debates on the ecological impact of cities.

Biological invasions are one of the greatest threats to biodiversity and ecosystem functioning. However, the constraints imposed by the invaders on native organisms and their associated response, remain poorly understood. Native species can survive invasion through multiple resistance strategies (avoidance, tolerance, or escape), but the relative importance of each strategy and how they vary among functional groups have been little explored. In this study, we examined the resistance strategies of native forbs and graminoids facing invasion by Solidago canadensis. First, we characterized the general impacts of invader density on native plant biomass production and diversity. Then, we investigated specific constraints linked to the invasion (competition for light, nutrients and mycorrhizal fungi), and the associated resistance strategies of native species. S. canadensis had different negative impacts on native vegetation biomass production and diversity - depending on functional groups - due to increased competition for light, nutrients, and mycorrhizal interactions. The increased competition for light was partially (1) avoided (tall forbs and graminoids) or (2) tolerated (small, shade-resistant graminoids). The effects of (3) allelopathic compounds and (4) increased competition for nutrients were avoided by some forbs (high mycorrhizal infection rates). Finally, some forbs and graminoids (5) escaped all constraints by completing their cycle early in the season. Our results highlight the diversity of non-exclusive strategies (avoidance, tolerance, escape) by which different functional groups can respond to invasion-induced constraints. They suggest that to improve understanding of the mechanisms underlying invasion, the native community responses should be decomposed into strategies specific to functional groups.