Local and landscape responses of biodiversity in calcareous grasslands

Herbivory is one of the most important antagonistic insect–plant interactions and can be influenced by factors at local and landscape scales. Landscape fragmentation may reduce herbivory directly (i.e., decreasing abundance and species richness of herbivores), but also indirectly increase herbivory (i.e., releasing herbivores from top‐down control). At a local scale, reduced plant diversity may enhance herbivory through lessened associated resistance, while resource availability (i.e., higher vegetation height and cover) may promote herbivory. Few studies have simultaneously considered the influence of local and landscape variables on insect herbivory. We evaluate effects of landscape (fragment size, connectivity, and arable land percentage) and local factors (plant cover and height and plant species richness) on insect herbivory in fragmented calcareous grasslands. Further, we ask whether these effects depend on feeding traits of herbivores (chewers vs. suckers) and habitat specialization of plants (specialists vs. generalists). Results show that herbivory was best explained by models including variables at both local and landscape scales. However, local factors were more important than landscape variables. Herbivory was in all cases positively related to height of herbs (i.e., taller and more heterogeneous food resources), whereas the effect of plant species richness varied with feeding traits of herbivores. Herbivory by chewers, which are commonly more generalist feeders, was negatively affected by plant species richness, supporting the idea of associated plant resistance. In contrast, herbivory by suckers, which tend to be more specialized, increased with plant richness. Although there was little influence of landscape scale, herbivory on specialist plants was significantly higher in smaller grasslands probably as a consequence of herbivore release from natural enemies. Functional redundancy among herbivore species would allow to maintain overall herbivory in fragmented calcareous grasslands. This study highlights the need to consider different herbivore and plant traits for a better understanding of herbivory responses to local and landscape factors.

Summary 1. Calcareous grasslands are diversity hotspots for plant and butterfly species in Europe, but connectivity of these grasslands has been reduced by habitat loss and fragmentation in recent decades. Reduced habitat area leads to biodiversity loss, but the significance of habitat connectivity independent of patch size and habitat quality is unclear. 2. Here, we focus on the impact of habitat connectivity on both butterfly and plant species richness and compare (i) a connectivity index, (ii) percentage habitat cover and (iii) distance to the next suitable habitat patch as alternative measures of connectivity. Species were recorded in 2007 in northern Bavaria (Germany) in paired large and small study sites in 31 independent landscapes. 3. We found that total loss of grassland connectivity would reduce species richness of specialist butterflies (38–69%) and specialist plants (24–37%). A connectivity index combining patch size and distance in the surrounding landscape was a better measure of connectivity than percentage habitat cover or distance to the next suitable habitat. 4. Species richness, species density and abundance of habitat‐specialist butterflies and plants were significantly higher in large compared with small study sites. 5. Synthesis and applications. We conclude that connectivity is highly relevant for conservation of butterfly and plant species with specialized habitat requirements, but the decision as to which connectivity measure is most appropriate depends on patch configuration, landscape context and study design. We suggest that management strategies should aim to increase connectivity by active restoration of former calcareous grasslands to ensure long‐term survival of habitat‐specialist species.

An important function of agri-environmental schemes (AES) is to change management of pastures to better conserve biodiversity. However, the effects of most AES on biodiversity are poorly understood, especially when it comes to effects of AES management over time. The main aim of this study is to investigate if the species richness and abundance of grassland specialists of vascular plants and two important insect pollinator groups (bumblebees and butterflies) differ over time (5 years) in pastures with AES management (two value levels; general values and special values) and pastures without AES management. We also investigate if local vegetation characteristics and landscape composition relate to species richness in semi-natural grasslands. Using data from more than 400 sites we found that species richness of vascular plants (grassland specialists) was higher in pastures with AES management (for special and general values) compared to those without AES, which implies that these schemes do have value of the conservation of plant diversity. However, species richness and abundance of butterflies (grassland specialists) and bumblebees (all species) did not differ significantly among the three AES categories. We found no evidence that the type of AES management caused any changes in species richness of plants, butterflies or bumblebees during the 5 year period of our investigation. It appears that AES management that encourages uniform and minimum levels of grazing can have both positive and negative effects on biodiversity. For example, pollinators may benefit from a lower grazing intensity that could increase flower richness and heterogeneity in vegetation height. However, low grazing intensity may lead to increased cover of trees and shrubs, which can have negative effects for both insect pollinators and vascular plants. The effects of landscape composition were weak and only species richness of bumble bees were associated with landscape composition. Designing management regimes to maintain suitably heterogeneous vegetation layer, and continued long-term monitoring of biodiversity will be critical for safeguarding culturally and functionally important semi-natural grasslands.

AimSpecies are lost world‐wide because of habitat destruction and fragmentation. Impacted communities can exhibit transient dynamics in response to such environmental changes, where slow extinctions and immigration delay the arrival to a new equilibrium. Life history traits such as generation time, resource use and dispersal capacity, as well as landscape history can be expected to affect possible extinction debt, but few have examined this for multiple taxa in the same study and particularly so for arthropods. The aim was to assess under which current and historical land use circumstances an extinction debt occurs for vascular plants and three insect taxa.LocationSouth‐eastern Sweden.MethodWe sampled current species richness of habitat specialist and generalist butterflies, bees, hoverflies, and vascular plants in 45 dry to mesic semi‐natural grassland fragments of various size and degree of connectivity, and situated in landscapes with contrasting land use conversion history. Habitat loss was estimated in each landscape by comparing modern maps to ~45 year old digitized aerial photographs. An extinction debt can be assumed if historical habitat size and connectivity better explain current species distribution than current habitat variables do.ResultsBees responded rapidly to habitat loss possibly as a result of their primary nesting resource being destroyed. Interestingly, species richness of specialist plants was best explained by historical habitat connectivity, richness of hoverflies by historical habitat area, and richness of butterflies by both historical habitat area and connectivity, indicating extinction debt for these taxa. Habitat generalist butterflies and hoverflies, but not plants and bees, exhibited extinction debt mainly in relation to habitat area. No effect of landscape type was found on the observed extinction debt.Main conclusionsSlow extinctions of persistent and long‐lived plants might explain extinction debt for both plants and herbivorous insects linked to these plants.

Burnets were surveyed in 100 semi-natural pastures in the province of Östergötland, southeastern Sweden. We analysed the presence/absence of burnets in relation to habitat characteristics, and species richness of butterflies and plants. Five species were found (Adscita statices, Zygaena osterodensis, Z. viciae, Z. filipendulae and Z. lonicerae), all occurring in 33%–36% of the localities. Among these, four are nationally red-listed. More species were found on (1) large semi-natural pastures, compared with small, (2) low- to medium-grazed semi-natural pastures, compared with heavily grazed, and (3) open semi-natural pastures, compared with wooded. A. statices and Z. viciae had a higher frequency of occupancy at localities surrounded by a large density of pastures, but the occurence of the other species did not rely on this variable. The number of burnet species per locality was positively correlated with the number of butterfly species, and slightly positively correlated with species richness of plants. The difference in species richness among burnets, butterflies and plants may be explained by different responses to grazing pressure; the species richness of burnets and butterflies peaked in localities with a lowgrazing pressure, while species richness of plants was unaffected by grazing. As burnets are easily surveyed and indicate a high butterfly-species richness, they may be suitable indicators of species richness of pastures. As uniform management with heavy grazing is detrimental for burnets and for many butterflies, it should be avoided at localities with a speciesrich fauna.

There is an increasing awareness that not only area and isolation, but also the characteristics of the landscape surrounding habitat patches influence population persistence and species diversity in fragmented landscapes. In this study, we examine the effects of grassland fragmentation and land use in the landscape matrix (on a 2 km scale) on species richness of plants, butterflies, bees and hoverflies. These organisms were studied in replicated remnant patches of different sizes and isolation, embedded in landscapes dominated either by forest, arable land or a mix of these. We found positive effects of patch area on species richness of the three insect taxa, but not of plants. Isolation had a negative effect only on hoverflies. Matrix type had contrasting effects on the studied taxa. Species richness of plants and butterflies was lowest in patches in landscapes dominated by arable land and highest in forest‐dominated landscapes. For hoverflies, the negative effect of small patch area was strongest in forest‐dominated landscapes, and there was a similar non‐significant trend for bees. Our study shows the importance of considering matrix characteristics when studying responses to habitat fragmentation. Differences in matrix response among organism groups probably impinge on differing mechanisms. A forest matrix is likely to provide additional resources for butterflies but either constitute a barrier to dispersal or deprive resources as compared to an arable matrix for hoverflies. Enhanced plant diversity in grassland patches embedded in forested landscapes can be explained by habitat generalists more easily invading these patches, or by an unpaid extinction debt in these landscapes.

Novel grassland habitats along linear infrastructure have gained attention as potential supplementary or replacement habitats for species suffering from the widespread loss of traditionally managed semi‐natural grasslands. However, it can take time for species to colonise new habitats, and both the historical and the current landscape composition can affect colonisation rates, particularly for grassland specialist species. We investigated the influence of more than 100 years of landscape history on present‐day species richness of plants, butterflies and bumblebees in two types of linear infrastructure habitats: road verges and power line corridors. We analysed the effects of time since habitat establishment and the amount of surrounding grassland cover in different time periods on species richness of the three taxa. Our results suggest a long time lag in the establishment of plant species in novel grassland habitats, with richness of butterflies and bumblebees largely dependent on the richness of plant species. There was no direct relationship between habitat age and the richness of butterflies or bumblebees, but we found unexpected legacy effects of grassland area on present‐day species richness. Higher richness of bumblebee species in road verges located in landscapes with larger surrounding grassland cover in the past is most likely a consequence of those landscapes containing a mosaic of afforested and abandoned grassland habitats today. Furthermore, we found that power line corridors might be important replacement habitats for butterflies in landscapes with little other grassland area left. Provided that road verges and power‐line corridors are managed appropriately, our results show that their species richness can be expected to increase in the future.

Different extinction debts among plants and arthropods after loss of grassland amount and connectivity

Calcareous grassland fragments as sources of bee pollinators for the surrounding agricultural landscape

This paper evaluates the long‐term effect of an ecological network of calcareous grasslands, a habitat type that experienced dramatic habitat loss and fragmentation during the 20th century, on species richness of habitat specialist plants. Calcareous grasslands are of special conservation concern as the habitat type with the highest diversity in plant and invertebrate species in central Europe. A baseline survey in 1989 established complete vascular plant species lists for all 62 previously abandoned calcareous grassland patches in the study area and assessed the presence of 48 habitat specialist plant species. An ecological network was initiated in 1989 to reconnect these patches with existing grazed pastures (core areas) through large flock sheep herding where feasible, as sheep are thought to be the primary dispersal vectors for calcareous grassland plants. An evaluation survey in 2009 showed significant increase in species richness of habitat specialist plants in patches reconnected by sheep herding, indicating successful colonizations by habitat specialist plants, while ungrazed patches showed no significant change. Observed increase in species richness between 1989 and 2009 was related to connectivity by sheep herding and the presence of a diversity of structural elements providing microsites for establishment. Baseline species richness of the patches, which had been abandoned since at least 1960, was associated with patch area, supporting the effect of ecological drift, and with vegetation type, which suggests that delays in extinction may be related to site factors governing the strength of competition with later seral species. The implementation of this ecological network represents a long‐term ‘natural experiment’ with baseline data, manipulation, and evaluation of hypothesized effects on a clearly defined target variable. It thus provides much needed empirical evidence that species loss in fragmented calcareous grassland communities can be counteracted by restoring functional connectivity among remnant patches.

Species richness and abundance of vascular plants and several groups of invertebrates (spiders, oribatid mites, diplopods, grasshoppers and bush crickets, ground beetles, butterflies and terrestrial gastropods) were recorded in three calcareous grasslands (Nenzlingen, Movelier and Vicques) in the northwestern Swiss Jura mountains. Species richness varied both between taxonomical groups and between sites (species richness ranges: 96-116 vascular plants, 60-66 spiders, 18 oribatid mites at each site, 1-7 diplopods, 10-16 grasshoppers and bush crickets, 19-21 ground beetles, 32-46 butterflies and 15-21 terrestrial gastropods). Species overlap (number of species that occured at all sites) was relatively large in terrestrial gastropods (59,1%), butterflies (56,5%), vascular plants (53,8%) and gasshoppers (47,1%), but relatively low in oribatid mites (32,3%), spiders (25,0%), ground beetles (18,4%) and diplopods (12,5%). Diversity expressed by the Shannon-Wiener index (H') was compared for five groups of invertebrates. Diversity was largest in spiders and ground beetles and lowest in terrestrial gastropods. Different taxonomical groups had their maximum diversity at different sites: each grassland had the highest diversity in a least one groupe. The three sites also varied in the abundance of different invertebrate groups. Most groups had the highest densities in Nenzlingen and the lowest densities in Vicques. All three sites contained a high proportion of species listed in the Red Data Book of Switzerland with values averaging 49,5% in grasshoppers and buch crickets, 28,9% in butterflies, 18,9% in vascular plants, 11,2% in terrestrial gastropods, and 6,7% in ground beetles. One spieder species (Oxyptila pullata) and two mite species (Epilohmannia cylindrica minima and Pergalumna myrmophila) were recorded for the first time in Switzerland.

Background and Objectives: As urbanisation is a significant global trend, there is a profound need for biodiversity protection in urban ecosystems. Moreover, the potential of urban green space to support urban biodiversity should be appreciated. Butterflies are environmental indicators that are sensitive to urbanisation. Therefore, it is important to identify butterfly distribution patterns and the factors influencing butterfly diversity and species composition in urban parks within cities. Research Highlights: To our knowledge, ours is the first study evaluating the effects of both land cover and local habitat features on butterfly species composition in urban parks of Beijing, China. Materials and Methods: In this study, we surveyed butterfly richness and abundance in 28 urban parks in Beijing, China. The parks differed in age and location in the urban area. Meanwhile, we investigated the green space in the surroundings of the parks at multi-spatial scales at the landscape level. We also investigated local park characteristics including the age of the park (Age), perimeter/area ratio of the park (SQPRA), area of the park (ha) (Area), green space cover within the park (Greenp), nectar plant species richness (Necpl), abundance of flowering nectar plants (Necabu) and overall plant species richness (Pl). Generalised linear models (GLMs) and redundancy discriminant analysis (RDA) were applied to relate butterfly diversity and butterfly species composition to environmental variables, respectively. Results: We recorded 3617 individuals belonging to 26 species from July to September in 2019. Parks on the city fringe had significantly higher butterfly diversity. Butterfly species richness was mostly related to total plant richness. The abundance of flowering nectar plants was closely linked to butterfly abundance. Land cover had little impact on butterfly diversity and community structure in urban parks. Conclusions: Once a park has sufficient plants and nectar resources, it becomes a useful haven for urban butterflies, regardless of the surrounding land cover. Well-planned urban parks focused on local habitat quality support butterfly conservation.

Patch occupancy of grassland specialists: Habitat quality matters more than habitat connectivity

Aim Biodiversity across the globe is heavily eroded by intensified management at local and landscape scales. Species communities of calcareous grasslands, which are among Europe's most diverse habitats, are severely threatened by the cessation of appropriate traditional management, loss of habitat connectivity and simplification of the surrounding landscape. However, our understanding of these often interrelated factors remains limited, in particular for trait-mediated responses across taxa. Here, we test the independent effects of local management (grazing, mowing and abandonment), habitat connectivity (measured by a connectivity index) and landscape complexity (indicated by the percentage of arable land) on nine taxa: plants, butterflies, bees, grasshoppers, hoverflies, spiders, true bugs, rove beetles and leafhoppers on small semi-natural calcareous grassland remnants (< 1 ha). Location Central Germany. Methods We use a joint analysis across taxa to identify general and trait-mediated responses (body size and Red List status) in species richness, abundance and community composition. Results We identified three key drivers of local diversity patterns: First, an increasing proportion of arable land from 10% to 80% led to a 29% loss of overall species richness. Second, despite differences between taxa, increasing habitat connectivity generally enhanced species richness. Connectivity effects were more accentuated in the large species per taxon, which can be expected to be good dispersers. Finally, grazing reduced species richness and abundance much more than annual mowing or short-term abandonment (5–15 years), in particular for red-listed species. We attribute this to plant resource removal through overgrazing and trampling. Main conclusions For the conservation management of small calcareous grasslands, we advocate an alternating strategy of mowing or lenient grazing and short-term abandonment, prioritizing connected fragments surrounded by diverse landscapes. Despite taxon-specific responses, our study across nine taxa demonstrates universal, trait-mediated effects of management, landscape complexity and connectivity on local biodiversity in fragmented communities.

Agricultural intensification has caused drastic declines in the area and species richness of semi-natural grasslands across Europe. Novel habitats, such as power line clearings, provide alternative habitats and niches for grassland species, and might therefore mitigate these declines. However, it is not fully understood which environmental factors determine the occurrence of grassland species in the clearings. Identifying the most important drivers for grassland species occurrence would help understand the value of the clearings for grassland conservation and target enhanced management into clearings with most potential as grassland habitat. We studied the effects of local environmental conditions, and past and present connectivity to semi-natural grasslands, on the species richness of grassland plants and butterflies in 43 power line clearings in Finland. The results of generalized linear models and hierarchical partitioning showed that increasing time since clear-cut and amount of clearing residue decreased the species richness of both species groups, while the cover of mesic habitats increased it. However, the two species groups showed also divergent responses. Present-day local environmental conditions appeared to be the sole driver of grassland butterfly species richness, whereas the richness of grassland plants was related both to current conditions and historical connectivity to grasslands in 1870–1880s. This suggests the presence of an extinction debt in the studied grassland plant communities, emphasizing the need for enhanced management to increase suitable grassland habitat in the clearings. This would diminish the potential future losses of grassland plant species in the clearings and create valuable habitat for grassland butterflies as well.