Climate and land-use changes are main drivers of insect declines, but their combined effects have not yet been quantified over large spatiotemporal scales. We analysed changes in the distribution (mean occupancy of squares) of 390 insect species (butterflies, grasshoppers, dragonflies), using 1.45 million records from across bioclimatic gradients of Switzerland between 1980 and 2020. We found no overall decline, but strong increases and decreases in the distributions of different species. For species that showed strongest increases (25% quantile), the average proportion of occupied squares increased in 40 years by 0.128 (95% credible interval: 0.123–0.132), which equals an average increase in mean occupancy of 71.3% (95% CI: 67.4–75.1%) relative to their 40-year mean occupancy. For species that showed strongest declines (25% quantile), the average proportion decreased by 0.0660 (95% CI: 0.0613–0.0709), equalling an average decrease in mean occupancy of 58.3% (95% CI: 52.2–64.4%). Decreases were strongest for narrow-ranged, specialised, and cold-adapted species. Short-term distribution changes were associated to both climate changes and regional land-use changes. Moreover, interactive effects between climate and regional land-use changes confirm that the various drivers of global change can have even greater impacts on biodiversity in combination than alone. In contrast, 40-year distribution changes were not clearly related to regional land-use changes, potentially reflecting mixed changes in local land use after 1980. Climate warming however was strongly linked to 40-year changes, indicating its key role in driving insect trends of temperate regions in recent decades.

Semi‐natural habitats provide important resources for wild bees in agricultural landscapes. Landscapes under management are dynamic and floral resources fluctuate in space and time. Thus, promoting different semi‐natural habitat types within landscapes could be key to support diverse bee meta‐communities throughout the season. Here, we integrate analyses of α‐diversity (species richness) and β‐diversity and species‐habitat networks to examine the relative contribution of all major semi‐natural habitats to wild bee meta‐communities in agricultural landscapes. We sampled extensively and conventionally managed meadows, flower strips, hedgerows and forest edges in spring, early and late summer in 25 landscapes in Switzerland. Habitat types varied in their importance for wild bees throughout the season: While extensively managed meadows supported more rare species, habitat specialists and bee species overall than the other habitat types, flower strips were most important later in the season. Each of the five investigated habitat types harboured relatively unique sets of species with different habitats generally acting as distinct modules in the overall bee‐habitat network. Not only flower richness in a habitat per se, but also flower‐habitat network properties (habitat strength and functional complementarity) were good predictors of wild bee richness. In addition to local floral richness, landscape composition and configuration interactively influenced β‐diversity patterns across habitats. Synthesis and applications. Our study highlights the value of pollinator‐habitat network analysis to inform pollinator conservation management at the landscape scale, especially when combined with information on floral resources and flower‐habitat networks. Maintaining different types of semi‐natural habitats offers diverse and complementary resources throughout the season, which are crucial to sustain diverse wild bee meta‐communities in agricultural landscapes. Particularly meadow extensification schemes can play a key role in safeguarding rare and specialist species in these landscapes. While locally a high flower richness promoted bee abundance and richness in general, our results indicate that increasing connectivity between habitat patches in landscapes dominated by arable crops appears to improve species exchange between local bee communities of different habitats, thereby possibly increasing their resilience to disturbances.

1. Understanding how multi-scale environmental heterogeneity shapes the structure and functions of animal and plant communities is pivotal in agroecology. Our capacity to ensure the provision of ecosystem services (ES), the sustainability of agroecosystems and the efficiency of agri-environmental schemes (AES) relies on this knowledge.2. There is growing interest in how biodiversity and ES are affected by the interplay between landscape characteristics and agricultural management (e.g., intermediate landscape complexity hypothesis; ILCH). However, studies have typically focused on classical measures of community structure (e.g., species abundance, richness and biodiversity), tending to neglect the effects on the structure and stability of ecological networks and the increased risk of biotic homogenization (i.e., loss of β-diversity).3. In this work, we use bee trap nests to sample pollen-solitary bee mutualistic networks in 9 pairs of olive groves under different management regimes (conventional vs. organic) in a landscape complexity gradient in southern Spain. We analyse the mutualistic networks at farm level to test the ILCH and study how agricultural practices and landscape complexity interact to affect the properties of these networks. We also explore the effects on spatial biotic homogenization by performing multivariate analyses of the composition and abundance of bee-plant communities and their pairwise interactions. The results show that solitary bee-plant networks have greater complexity andstability on organic olive farms embedded in relatively heterogeneous landscapes.Differences from conventional management were higher in landscapes of intermediate complexity but were non-significant on olive farms located in simpler landscapes. β-diversity of bees, plants and their pairwise interactions was also greater on organic olive farms. 5. In conclusion, human-induced environmental heterogeneity interacts at different scales to shape plant-solitary bee networks in olive groves, which may have important implications for ES provision and the effectiveness of agri-environmental measures. K E Y W O R D Sbiotic homogenization, landscape structure, mutualistic networks, network complexity, organic farming, plant-pollinator interactions, trap nests, β-diversity | 2317Functional Ecology MARTÍNEZ-NÚÑEZ ET Al.

This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

One of the current challenges for applied ecologists is to understand how to manage/restore agroecosystems in a sustainable and cost‐effective way. The intermediate landscape complexity hypothesis (ILCH) predicts that the effectiveness of agri‐environmental measures (AES) on biodiversity and ecosystem services recovery is often largest in landscapes of intermediate complexity. This hypothesis has rarely been tested in savanna‐like permanent agroecosystems. Focusing on pollinators, we test the ILCH at the regional scale in Mediterranean olive orchards, one of the most important permanent agroecosystems in the world. We inferred abundance of cavity‐nesting pollinators in 40 paired olive orchards (extensively vs. intensively managed herbaceous cover) in 20 localities selected across a landscape complexity gradient. We also studied how different magnitudes in local management switches may affect pollinators by considering organic and intensive fields as management extremes in olive orchards. We used 208 trap nests for solitary bees to measure colonization rates. Additionally, we conducted pollinator surveys to ascertain that colonization rate was a representative proxy for pollinator activity. Our results showed that (a) changes in colonization rates due to local herb cover management peaked at intermediate landscape complexity, with extensively managed fields rendering higher colonization rates. (b) Organic fields had higher colonization rates than their control farms regardless of landscape complexity. (c) There was a highly significant correlation between nest colonization rates and density of pollinators foraging on flowers, which suggests that colonization rate is a good estimator of pollinator activity. Policy implications. The maintenance of ground herb cover (main agri‐environmental measure in olive orchards) is a cost‐effective investment allowing recuperation of pollinators when targeting olive farms located in landscapes of intermediate complexity. Additionally, fostering organic farming (still minority in olive groves) for the conservation of solitary bees should be a priority for policymakers since its effects are beneficial in any landscape.