Restoration of semi-natural grasslands, a success for phytophagous beetles (Curculionidae)

Semi-natural pastures have rich plant and animal communities of high conservation value which depend on extensive management. As the area of such land decreases, abandoned semi-natural grasslands have been restored to re-establish biodiversity. Restoration schemes, which include thinning of woody plants and reintroduction of grazing, are mainly designed according to the responses of well-studied groups (such as vascular plants and birds). Weevils (Curculionidae) are a very diverse phytophagous beetle family. Here, we evaluated the restoration success of pastures for weevils (Curculionidae), by comparing their species diversity in abandoned, restored, and continuously grazed semi-natural pastures on 24 sites in central Sweden. Weevils were sampled by sweep-netting. We recorded 3019 weevil individuals belonging to 104 species. There was no statistically significant difference in species numbers between the pasture management treatments. However, weevil species composition of abandoned pastures differed from those in restored and continuously managed pastures, but there was no significant difference in community composition between restored and continuously grazed pastures. The abandoned sites tended to be dominated by polyphagous species, whereas the grazed sites contained more monophagous and oligophagous species. The number of weevil species was positively related to understory vegetation height and connectivity to other semi-natural grasslands and negatively related to the cover of trees and shrubs in the pastures. We conclude that restoration of abandoned semi-natural pastures is a good approach to restore weevil communities. To maintain a species rich weevil community, pastures should be managed to be relatively open, but still have patches of tall field- layer vegetation. Restoration and conservation measures should primarily be targeted on regions and landscapes where a high proportion of semi-natural grassland stil

Restoration of semi-natural grasslands, a success for phytophagous beetles (Curculionidae)

Semi-natural pastures have rich plant and animal communities of high conservation value which depend on extensive management. As the area of such land decreases, abandoned semi-natural grasslands have been restored to re-establish biodiversity. Restoration schemes, which include thinning of woody plants and reintroduction of grazing, are mainly designed according to the responses of well-studied groups (such as vascular plants and birds). Weevils (Curculionidae) are a very diverse phytophagous beetle family. Here, we evaluated the restoration success of pastures for weevils (Curculionidae), by comparing their species diversity in abandoned, restored, and continuously grazed semi-natural pastures on 24 sites in central Sweden. Weevils were sampled by sweep-netting. We recorded 3019 weevil individuals belonging to 104 species. There was no statistically significant difference in species numbers between the pasture management treatments. However, weevil species composition of abandoned pastures differed from those in restored and continuously managed pastures, but there was no significant difference in community composition between restored and continuously grazed pastures. The abandoned sites tended to be dominated by polyphagous species, whereas the grazed sites contained more monophagous and oligophagous species. The number of weevil species was positively related to understory vegetation height and connectivity to other semi-natural grasslands and negatively related to the cover of trees and shrubs in the pastures. We conclude that restoration of abandoned semi-natural pastures is a good approach to restore weevil communities. To maintain a species rich weevil community, pastures should be managed to be relatively open, but still have patches of tall field-layer vegetation. Restoration and conservation measures should primarily be targeted on regions and landscapes where a high proportion of semi-natural grassland still remains

Restoration of plant and pollinator communities in fragmented grasslands

A large proportion of the former area of species-rich semi-natural grasslands has been lost due to agricultural intensification and abandonment. Remaining small and isolated grassland fragments are often imbedded in more or less intensively managed landscapes. The loss and fragmentation of these grasslands have profound effects on overall biodiversity, and may affect processes and functions in the entire agricultural landscape. Therefore, semi-natural grasslands are key targets for conservation and restoration efforts. Until recently, evaluations have mainly assessed restoration outcomes in terms of species richness and abundance, often only of plants. Contrasting responses among interacting species to landscape and local factors can have consequences for the recovery of community composition, species interactions and ecosystem functions in restored habitat fragments. In this thesis, I examine the response of plant and pollinator (bees; Apoidea, and hoverflies; Syrphidae) communities to restoration of semi-natural grasslands in fragmented landscapes in south-central Sweden. Restoration effects were measured in terms of species richness, species composition, community trait composition, and composition of species and interactions within plant-pollinator networks. Following restoration, plant communities recovered both in terms of species richness and trait composition. These changes were reflected in a recovery of pollinator composition within plant-pollinator networks, and also a recovery in species interactions. The trait composition among pollinators was sustained both through abandonment and restoration, but responded to structural features of the vegetation. Plant communities had higher species richness in sites adjacent to intact grasslands than in those adjoining croplands. Hoverflies were not affected by grassland connectivity, but high connectivity facilitated the recovery of sedentary and specialized bee species. Time since restoration was an important driver in the recovery of plant communities, but not for pollinators or species interactions. This thesis shows that plant and pollinator communities as well as plant-pollinator interactions can be restored. The dispersal ability of both plants and pollinators, and the resource use of pollinators within and outside grassland fragments affected species responses to grassland connectivity. Connectivity to intact grasslands does not fully reflect the availability of resources and potential source populations within fragmented landscapes. Except for intact grasslands, abandoned and restored grasslands are also important for biodiversity and ecosystem functioning in the agricultural landscape

Plant-pollinator diversity indices per study site

Data table with the information associated to each study site: name, coordinates, grassland category (abandoned, restored or continuously grazed), landscape connectivity index, flowering plant diversity variables (abundance, species richness, species evennes, functional richness and functional evenness) and bee and hoverfly diversity variables (abundance, species richness, species evennes, functional richness and functional evenness)

Pollinator foraging flexibility mediates rapid plant-pollinator network restoration in semi-natural grasslands

We examined how plant-pollinator interactions were affected by time since habitat restoration and landscape connectivity by comparing plant-pollinator networks in restored, abandoned and continuously grazed semi-natural pastures in south-central Sweden. We measured richness of flowering plants and pollinators, and local plant-pollinator network characteristics including species composition as well as the number and identity of interactions, allowing a deeper understanding of species and interaction beta diversity. Pollinator richness and abundance were highest in restored grasslands. They successfully resembled continuously grazed grasslands. However, the turnover of interactions was extremely high among pasture categories (0.99) mainly due to high turnover of plant (0.74) and pollinator species (0.81). Among co-occurring plant and pollinator species, the turnover of interactions (0.66) was attributable mainly to differences in the number of links and to a lesser extent to species true rewiring (~0.17). Connectivity and time since restoration had no effect on the measured network properties. We show that plant-pollinator interactions can be rapidly restored even in relatively isolated grasslands. This is partly due to flexibility of most pollinators to establish interactions with the available flowering plants and relatively high species interaction rewiring, indicating that pollinators behavioural plasticity allow them to shift diets to adapt to new situations.Peer reviewe

Mobility and resource use influence the occurrence of pollinating insects in restored seminatural grassland fragments

After habitat restoration, species need to recolonize from existing populations. The ability of species to recolonize restored habitats likely depends on their traits. This study aimed to test if species traits and isolation from source habitat can explain the presence of insects in restored grasslands. We surveyed the occurrence of hoverflies and bees in 14 restored seminatural pastures as well as in intact seminatural grasslands in the surrounding landscape. We tested how connectivity, time since restoration, and species traits influence if species that are present in the surrounding landscape also occur in restored pastures. Solitary bee species present in the landscape were less likely to occur in restored pastures compared to bumblebees and hoverflies. The occurrence of bumblebees, but not solitary bees or hoverflies, decreased with time since restoration. The occurrence of solitary bees increased but the occurrence of hoverflies decreased with high connectivity. Migratory hoverflies were more likely to occur in restored pastures than nonmigratory hoverflies, especially in pastures with low connectivity. Among both bumblebees and solitary bees, the occurrence was influenced by nesting traits, with the lowest occurrence of parasitic species and of species digging nests in the ground. The subset of the landscape's species pool that occurs in restored pastures has a contrasting set of traits compared with species in intact source habitats. Both mobility and resource use act as filters that influence the assembly of pollinator communities after restoration. A full recovery of pollinator communities is more likely if source populations are available nearby