Extinction debt in a common grassland species: immediate and delayed responses of plant and population fitness

Changes in landscape structure and environmental conditions due to habitat fragmentation can have significant effects on plant populations. Decreasing genetic diversity and changing population structure can reduce plant fitness and influence the long-term persistence of populations. Dry calcareous grasslands in Estonia have witnessed a large decline in area within the last 80 years, but due to extinction debt, the species richness in these grasslands has not yet responded to this decline. In these calcareous grasslands, we studied genetic diversity, phenotypic performance and population characteristics of a common habitat-specialist grass, Briza media. A decrease in genetic diversity was associated with a decrease in plant reproductive output. In addition, we found that some fitness components of B. media showed a delayed response to landscape changes. Specifically, plant height and germination success were related to historical rather than to current landscape parameters, indicating a time-lagged response of plant performance to habitat fragmentation. Dependence on historical landscape structure may thus result in a future decline in population fitness even if habitat loss and fragmentation no longer continue. The documented effect of current environmental conditions, however, shows that fitness-related traits are already slowly adapting to the changing conditions. Our results indicate that even common habitat-specialist species can be susceptible to landscape changes and be threatened by decreased population performance in the future.     

Effects of habitat area, isolation, and landscape diversity on plant species richness of calcareous grasslands

Calcareous grasslands harbour a high biodiversity, but are highly fragmented and endangered in central Europe. We tested the relative importance of habitat area, habitat isolation, and landscape diversity for species richness of vascular plants. Plants were recorded on 31 calcareous grasslands in the vicinity of the city of Göttingen (Germany) and were divided into habitat specialist and generalist species. We expected that habitat specialists were more affected by area and isolation, and habitat generalists more by landscape diversity. In multiple regression analysis, the species richness of habitat specialists (n = 66 species) and habitat generalists (n = 242) increased with habitat area, while habitat isolation or landscape diversity did not have significant effects. Contrary to predictions, habitat specialists were not more affected by reduced habitat area than generalists. This may have been caused by delayed extinction of long-living plant specialists in small grasslands. Additionally, non-specialists may profit more from high habitat heterogeneity in large grasslands compared to habitat specialists. Although habitat isolation and landscape diversity revealed no significant effect on local plant diversity, only an average of 54% of habitat specialists of the total species pool were found within one study site. In conclusion, habitat area was important for plant species conservation, but regional variation between habitats contributed also an important 46% of total species richness.     

Process‐based long‐term evaluation of an ecological network of calcareous grasslands connected by sheep herding

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 diversity of remnant calcareous grasslands in south eastern Germany depends on litter cover and landscape structure

Species diversity depends on, often interfering, multiple ecological drivers. Comprehensive approaches are hence needed to understand the mechanisms determining species diversity. In this study, we analysed the impact of vegetation structure, soil properties and fragmentation on the plant species diversity of remnant calcareous grasslands, therefore, in a comparative approach.We determined plant species diversity of 18 calcareous grasslands in south eastern Germany including all species and grassland specialists separately. Furthermore, we analysed the spatial structure of the grasslands as a result of fragmentation during the last 150 years (habitat area, distance to the nearest calcareous grassland and connectivity in 1830 and 2013). We also collected data concerning the vegetation structure (height of the vegetation, cover of bare soil, grass and litter) and the soil properties (content of phosphorous and potassium, ratio of carbon and nitrogen) of the grassland patches. Data were analysed using Bayesian multiple regressions.We observed a habitat loss of nearly 80% and increasing isolation between grasslands since 1830. In the Bayesian multiple regressions the species diversity of the studied grasslands depended negatively on cover of litter and to a lower degree on the distance to the nearest calcareous grassland in 2013, whereas soil properties had no significant impact.Our study supports the observation that vegetation structure, which strongly depends on land use, is often more important for the species richness of calcareous grasslands than fragmentation or soil properties. Even small and isolated grasslands may, therefore, contribute significantly to the conservation of species diversity, when they are still grazed.     

Hybrid ecosystems can contribute to local biodiversity conservation

Calcareous grasslands have become severely threatened habitats in Europe. The aim of this study was to investigate the changes in plant species richness, and functional and phylogenetic diversity in northern Estonian calcareous (alvar) grasslands resampled after 90 years of land-use change. Functional traits characterizing species that have benefited most from decreased habitat area and altered environmental conditions, and additional species that can potentially inhabit the remaining grassland patches were identified. Also changes in the relative amount of habitat-specific species were studied to detect a possible decrease in habitat integrity. Although grasslands in the studied region had lost most of their original area (~90 %), species richness had substantially increased due to invasion by more competitive, nutrient-demanding native species. Functional diversity generally increased, whereas phylogenetic diversity showed no response to altered conditions. Overall, these grasslands have lost their integrity as calcareous grassland habitat type in the region, because the relative amount of habitat-specific characteristic species has declined significantly. However, although the grasslands have transformed to a ‘hybrid’ habitat type and restoration to their previous state is likely not reasonable, such degraded species-rich grassland fragments can still be recognized as important habitats to preserve high local biodiversity and several characteristic species of calcareous grasslands. As current landscapes consist of an increasing number of hybrid and novel communities, new tools to supplement traditional conservation or restoration practices are necessary to recognize and maintain regions and habitats of high local biodiversity.     

Tracking the effects of one century of habitat loss and fragmentation on calcareous grassland butterfly communities

Habitat loss and fragmentation are known to reduce patch sizes and increase their isolation, consequently leading to modifications in species richness and community structure. Calcareous grasslands are among the richest ecosystems in Europe for insect species. About 10% (1,150 ha) of the total area of a calcareous ridge region (Calestienne, Belgium) and its butterfly community was analysed over a timeframe of about 100 years. Since 1905 to present day (2005), the Calestienne region has undergone both calcareous grassland loss and fragmentation: not only did calcareous grassland size decrease and isolation increase, but also, the number of calcareous grassland patches within the landscape increased until 1965, and subsequently decreased, clearly reflecting the effects of fragmentation. These processes have had a profound effect on the butterfly community: extinction and rarefaction affected significantly more often specialist species, which means that generalist species are more and more overrepresented. This ecological drift, i.e. the replacement of specialists by generalists in species assemblages is likely to be a general effect of habitat loss and fragmentation on natural communities.     

Landscape‐ and small‐scale determinants of grassland species diversity: direct and indirect influences

Species richness is influenced both by mechanisms occurring at landscape scales, such as habitat availability, and local‐scale processes, that are related to abiotic conditions and plant–plant interactions. However, it is rarely tested to what extent local species richness can be explained by the combined effect of factors measured at multiple spatial scales. In this study, we quantified the simultaneous influence of historical landscape‐scale factors (past human population density, and past habitat availability – an index combining area and connectivity) and small‐scale environmental conditions (shrub cover, and heterogeneity of light, soil depth, and other soil environmental variables) on plant species richness in dry calcareous grasslands (alvars). By applying structural equation modelling (SEM) we found that both landscape conditions and local environmental factors had significant direct and indirect (i.e. through the modification of another factor), effects on species richness. At the landscape scale, we found a direct positive influence of historical habitat availability on species richness, and indirect positive influence of past human population (via its effects on historical habitat availability). At small scales, we found a positive direct influence of light heterogeneity and shrub cover on species richness. Conversely, we found that small‐scale soil environmental heterogeneity, which was mainly determined by soil depth heterogeneity, had a negative effect on species richness. Our study indicates that patterns of species richness in alvar grasslands are positively influenced by the anthropogenic management regime that maintained the landscape habitat conditions in the past. However, the abandonment of management, leading to shrub invasion and increased competition for light resources also influenced species richness. In contrast to the positive heterogeneity–diversity relationship we found that soil heterogeneity reduced species richness. Environmental heterogeneity, occurring at the plant neighbourhood scale (i.e. centimetres), can increase the isolation among suitable soil patches and thus hinder the normal functioning of populations. The combination of previous knowledge of the system with new ecological theories facilitates disentangling how species richness responds to complex relationships among factors operating at multiple scales.     

What determines Orthoptera species distribution and richness in temperate semi-natural dry grassland remnants?

Wide-spread fragmentation and isolation of habitats with high nature conservation value lends increasing importance to a better understanding of the factors which determine species richness in isolated habitat patches. Using data of one of the most abundant invertebrate groups in grasslands, Orthoptera, we analysed how species richness and distribution in 60 isolated semi-natural grassland remnants in Austria were affected by five environmental variables (altitude, habitat and land use diversity within each patch, habitat diversity of areas adjacent to each patch, patch size), and related to diversity of their main food source, i.e. vascular plants. We found a significant positive correlation between Orthoptera and vascular plant species richness, with threatened Orthoptera species having the lowest correlation coefficients. Life form diversity of plants was only moderately positively correlated with Orthoptera species richness. Habitat diversity within and adjacent to the grassland patch had by far the highest loadings on the first two axes of the principal component analysis, which jointly explained 99?% of the variance, and proved to be significant for total, threatened and not threatened Orthoptera, as well as for the two Orthoptera orders occurring in Central Europe (Caelifera, Ensifera). Additionally, the distribution of the majority of those 14 Orthoptera species analysed individually was mainly correlated with habitat diversity within and adjacent to the grassland patch. However, the distribution of a significant proportion of species was associated with other factors: five species were closely related to on-site land use diversity and patch size, and the distribution of three Ensifera species was not significantly correlated to any of the explanatory variables. We conclude that a surrogate taxa approach, i.e. the use of well-known taxonomic groups (e.g. vascular plants), may indeed deliver good results for capturing total, but less so for threatened, Orthoptera species richness in semi-natural grassland remnants. Small scale habitat diversity may be crucial to allow for the co-existence of a large number of Orthoptera species and has to be taken equally into account as patch size in nature conservation.     

Predictors of mammal species richness in KwaZulu-Natal,South Africa

The management of multi-functional landscapes warrants better knowledge of environment-richness associations at varying disturbance levels and habitat gradients. Intensive land-use patterns for agricultural purposes lead to fragmentation of natural habitat resulting in biodiversity loss that can be measured using landscape metrics to assess mammalian richness. Since carnivores and herbivores are likely to show different responses to disturbance, we calculated carnivore, non-carnivore, and total mammal species richness from camera surveys using a first order Jackknife Estimator. Richness was compared along a habitat gradient comprising coastal forest, Acacia thicket, and highland in KwaZulu-Natal, South Africa. We used standardized OLS regression models to identify climatic and disturbance variables, and landscape metrics as predictors of species richness. The estimated total and non-carnivore species richness were highest in coastal forest, while carnivore species richness was highest in highland followed by coastal forest and Acacia thicket. Average monthly maximum temperature was a significant predictor of all richness groups, and precipitation of the wettest month and isothermality determined total and non-carnivore species richness, respectively. These climatic variables possibly limit species distribution because of physiological tolerance of the species. Total mammal richness was determined by mean shape (+) and habitat division (−) while diversity (+) and patch richness (−) explained carnivore species richness. Mean shape index (+) influenced non-carnivore richness. However, habitat division and patch richness negatively influenced total mammal richness. Though habitat patch size and contiguity had a weak positive prediction, these metrics demonstrated the importance of habitat connectivity for maintaining mammal richness. The identification of these climatic and landscape patterns is important to facilitate future landscape management for mammal conservation in forest-mosaics.     

Woody elements benefit bird diversity to a larger extent than semi-natural grasslands in cereal-dominated landscapes

Increasing landscape complexity can mitigate negative effects of agricultural intensification on biodiversity by offering resources complementary to those provided in arable fields. In particular, grazed semi-natural grasslands and woody elements support farmland birds, but little is known about their relative effects on bird diversity and community composition. In addition, the relative importance of local habitat versus landscape composition remains unclear. We investigated how the presence of semi-natural grasslands, the number of woody elements and the composition of the wider agricultural landscape affect bird species richness, true diversity (exponential Shannon diversity) and species composition. Bird communities were surveyed four times on 16 paired transects of 250 m each with 8 transects placed between a crop field and a semi-natural grassland and 8 transects between two crop fields with no semi-natural grasslands in the vicinity. The number of woody elements around transects was selected as an important predictor in all models, having a positive effect on species richness and true diversity, while the local presence of semi-natural grasslands was not selected in the best models. However, species richness and true diversity increased with increasing cover of ley and semi-natural grasslands, whereas species composition was modified by the coverage of winter wheat at the landscape scale. Furthermore, bird species richness, true diversity and species composition differed between sampling dates. As bird diversity benefited from woody elements, rather than from the local presence of semi-natural grasslands as such, it is important to maintain woody structures in farmland. However, the positive effect of grassland at the landscape scale highlights the importance of habitat variability at multiple scales. Because species richness and true diversity were affected by different landscape components compared to species composition, a mosaic of land-use types is needed to achieve multiple conservation goals across agricultural landscapes.     

Trait-Specific Responses of Wild Bee Communities to Landscape Composition,Configuration and Local Factors

Land-use intensification and loss of semi-natural habitats have induced a severe decline of bee diversity in agricultural landscapes. Semi-natural habitats like calcareous grasslands are among the most important bee habitats in central Europe, but they are threatened by decreasing habitat area and quality, and by homogenization of the surrounding landscape affecting both landscape composition and configuration. In this study we tested the importance of habitat area, quality and connectivity as well as landscape composition and configuration on wild bees in calcareous grasslands. We made detailed trait-specific analyses as bees with different traits might differ in their response to the tested factors. Species richness and abundance of wild bees were surveyed on 23 calcareous grassland patches in Southern Germany with independent gradients in local and landscape factors. Total wild bee richness was positively affected by complex landscape configuration, large habitat area and high habitat quality (i.e. steep slopes). Cuckoo bee richness was positively affected by complex landscape configuration and large habitat area whereas habitat specialists were only affected by the local factors habitat area and habitat quality. Small social generalists were positively influenced by habitat area whereas large social generalists (bumblebees) were positively affected by landscape composition (high percentage of semi-natural habitats). Our results emphasize a strong dependence of habitat specialists on local habitat characteristics, whereas cuckoo bees and bumblebees are more likely affected by the surrounding landscape. We conclude that a combination of large high-quality patches and heterogeneous landscapes maintains high bee species richness and communities with diverse trait composition. Such diverse communities might stabilize pollination services provided to crops and wild plants on local and landscape scales.     

Extinction debt in fragmented grasslands: paid or not?

Fragmentation of grasslands and forests is considered a major threat to biodiversity. In the case of plants, the effect of fragmentation or landscape context is still unclear and published results are divergent. One explanation for this divergence is the slow response of long‐lived plants, creating an extinction debt. However, this has not been empirically confirmed. In this study, data were compiled from broad‐scale studies of grasslands from throughout the world that relate plant diversity to fragmentation effects. Only seven studies from northern Europe, out of a total 61, gave any information on actual habitat fragmentation in time and space. In landscapes with >10% grassland remaining, present‐day species richness was related to past landscape or habitat pattern. In landscapes with <10% grassland remaining, in contrast, plant species richness was more related to contemporary landscape or habitat pattern. Studies from landscapes with >10% grassland remaining supported the concept of an extinction debt, while studies from more fragmented landscapes did not provide any evidence of an extinction debt. In order to make generalisations about historical legacies on species diversity in grasslands it is important to consider a range of highly transformed landscapes, and not only landscapes with a high amount of grassland remaining.     

Diverse Effects of a Seven-Year Experimental Grassland Fragmentation on Major Invertebrate Groups

Habitat fragmentation is a major driver of biodiversity loss, but observed effects vary and may depend on the group examined. Time since fragmentation may explain some differences between taxonomical groups, as some species and thus species composition respond with a delay to changes in their environment. Impacts of drivers of global change may thus be underestimated in short-term studies. In our study we experimentally fragmented nutrient-poor dry calcareous grasslands and studied the response of species richness, individual density and species composition of various groups of invertebrates (gastropods, ants, ground beetles, rove beetles, orthoptera, spiders, woodlice) in 12 small (1.5 m * 1.5 m) and 12 large (4.5 m * 4.5 m) fragments and their corresponding control plots after 7 years. We further examined responses to fragmentation in relation to body size and habitat preferences. Responses to fragmentation varied between taxonomical groups. While spider species richness and individual density were lower in fragments, the opposite was true for an orthopteran species and woodlice. Species composition and β-diversity differed between fragments and control plots for some groups. However, the interaction treatment*plot size was rarely significant. Species with high occupancy rates in undisturbed control plots responded more negatively to the fragmentation, while species with large body size were relatively more abundant in fragments in some groups. No effect of the fragmentation was found for ants, which may have the longest lag times because of long-lived colonies. However, relationships between abundance and the species’ preferences for environmental factors affected by edge effects indicate that ant diversity too may be affected in the longer-term. Our results show the importance of considering different groups in conservation management in times of widespread fragmentation of landscapes. While species richness may respond slowly, changes in abundance related to habitat preferences or morphology may allow insights into likely long-term changes.     

西双版纳大卡老寨农地景观与物种保护的关系

应用参与式农村评估法从村级水平对西双版纳大卡老寨农地景观与物种保护关系进行了初步调查与分析。斑块物种丰富度与斑块的平均大小、破碎度和分离度相关性较复杂。由于橡胶、西番莲、砂仁斑块面积的迅速发展,多样性、均匀度有所增加,而以集体林为主的景观优势度下降,景观格局的改变使得物种保护呈现出两种不同结果,一是新增加的斑块类型使物种数增加,提高了农业生态系统的多样性,另一方面则是减少或消失的斑块类型造成物种流失。而森林景观是整个农地景观的重要环节,应严格加以保护和合理利用。     

Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks

Habitat loss and fragmentation affect species richness in fragmented habitats and can lead to immediate or time‐delayed species extinctions. Asynchronies in extinction and extinction debt between interacting species may have severe effects on ecological networks. However, these effects remain largely unknown. We evaluated the effects of habitat patch and landscape changes on antagonistic butterfly larvae–plant trophic networks in Mediterranean grasslands in which previous studies had shown the existence of extinction debt in plants but not in butterflies. We sampled current species richness of habitat‐specialist and generalist butterflies and vascular plants in 26 grasslands. We assessed the direct effects of historical and current patch and landscape characteristics on species richness and on butterfly larvae–plant trophic network metrics and robustness. Although positive species‐ and interactions–area relationships were found in all networks, structure and robustness was only affected by patch and landscape changes in networks involving the subset of butterfly specialists. Larger patches had more species (butterflies and host plants) and interactions but also more compartments, which decreased network connectance but increased network stability. Moreover, most likely due to the rescue effect, patch connectivity increased host‐plant species (but not butterfly) richness and total links, and network robustness in specialist networks. On the other hand, patch area loss decreased robustness in specialist butterfly larvae–plant networks and made them more prone to collapse against host plant extinctions. Finally, in all butterfly larvae–plant networks we also detected a past patch and landscape effect on network asymmetry, which indicates that there were different extinction rates and extinction debts for butterflies and host plants. We conclude that asynchronies in extinction and extinction debt in butterfly–plant networks provoked by patch and landscape changes caused changes in species richness and network links in all networks, as well as changes in network structure and robustness in specialist networks.     

Missing the target? A critical view on butterfly conservation efforts on calcareous grasslands in south-western Germany

Butterflies are strongly declining on grassland habitats of Central Europe. Therefore, the success of conservation measures on high quality grassland habitats is controversially discussed. We compared the changes in butterfly diversity and community structure on six managed calcareous grasslands with eight unmanaged vineyard fallows. We obtained strong losses of species diversity and remarkable shifts of community compositions on both habitat types. However, the changes on vineyard fallows were only slightly more severe but more stochastic than on the calcareous grasslands. The shifts in community composition with respect to functional species traits were rather similar between the two different grassland types so that complex butterfly communities evolved into generalist-dominated ones. Connectivity was higher among vineyard fallows than among calcareous grasslands. Consequently, conservation measures on calcareous grasslands only partly achieved their goal to maintain the high species diversity and functional complexity still observed in the 1970s. The negative impacts of eutrophication and monotonisation of the landscape as well as climate change are affecting all habitats, independently from management concepts. Therefore, management on conservation sites can buffer against these effects, but is not sufficient for a full compensation.     

Pattern of land mosaics affecting butterfly assemblage at Mt Ikoma, Osaka, Japan

We studied the effects of habitat mosaics on butterfly assemblage on multiple spatial scales: landscape, landscape element, local habitat, and microhabitat, based on the transect counts conducted along a 3.84 km route. The transect route, including 21 local habitats, passed through two distinct areas: 1.65 km of a secondary deciduous Quercus forest and the grove of a shrine in Hiraoka, and 2.19 km of a mosaic of secondary deciduous Quercus forest, grassland, and farmland in Narukawa. The diversity of the landscape elements and species richness were higher in Narukawa than in Hiraoka; the landscape mosaic enhanced the species richness in Narukawa. However, the diversity indices and specialist species (univoltine tree feeder) were decreased in this mosaic landscape. The species richness at local habitats was also increased by the mosaic of microhabitats, such as the herbaceous layer, glade, and mantle in the local habitats, whereas it was decreased by an abundant shrub layer. The ratios of species richness to abundance in the local habitats were lower than expected based on random sampling from the total of Hiraoka and Narukawa. This means that local assemblages were non-random samples from an assemblage on the landscape or regional scale, and were made up by the process of habitat selection of butterfly species in the assemblages on the landscape or regional scale. For conservation of butterfly assemblages, we recommend that woodlands should be kept without fragmentation, but with glades or small grasslands, and with clearance of the shrub layer along the path.     

The role of patch area and habitat diversity in explaining native plant species richness in disturbed suburban forest patches in northern Belgium

Relatively easy measurable patch characteristics (especially habitat diversity measures) have proven to be valuable indicators of forest plant species richness in forest fragments of relatively undisturbed areas. Urban and suburban forest patches, however, are characterized by a specific landscape ecological context implying that specific processes may influence ecosystem functioning and hence that other abiotic indicators for plant diversity are more appropriate. We studied the relation between functional ecological plant species groups and suburban forest patch characteristics such as patch area, habitat diversity and isolation. Some components of species richness were related to the isolation of the patches. In contrast to previous similar large-scale fragmentation studies in more rural areas, further results stressed the overwhelming importance of patch area relative to habitat variables in determining species richness. This suggests (1) the occurrence of density-dependent species extinction processes in small forest patches; or (2) the existence of external deterministic factors which put a major constraint on species richness in small patches. We tend to support the latter hypothesis and propose forest disturbance and associated black cherry (Prunus serotina Ehrh.) invasion as such a possible external factor. Small forest patches may be more sensitive to disturbance and biological invasion due to various reasons. Hence large forest patches are to be preferred for plant conservation in the suburban area.     

Heterogeneity fosters biodiversity: Linking history and ecology of dry calcareous grasslands

Calcareous grasslands in Central Europe harbour a high diversity of plant and animal species. However, as man-made habitats, they need to be managed in order to maintain high species diversity. Conservation efforts often aim at reintroducing historical management regimes, such as regular grazing or mowing. Despite such efforts, the diversity and number of species of calcareous grasslands is still decreasing. We propose that, besides fragmentation and eutrophication, a lack of structural heterogeneity within and around calcareous grasslands as created by historic management is causing species loss as well. Here, we review the literature on the history of calcareous grassland management in northern Switzerland, the heterogeneity that it created and the relevance of this heterogeneity for biodiversity at three spatial scales: (1) within grasslands, (2) in their close surroundings and (3) at the landscape scale. Considering that historic management has created heterogeneity at all three scales and that many species do indeed depend on this structural diversity, we conclude that in order to conserve the full range of biodiversity associated with calcareous grasslands, conservation management should aim at increasing heterogeneity in, around, and between grasslands.     

Conserving butterflies in fragmented plantation forests: are edge and interior habitats equally important?

Edge effects are increasing in forest-dominated landscapes worldwide, due to increased fragmentation by other land uses. Understanding how species respond to edges is therefore critical to define adequate conservation measures. We compared the relative importance of interior and edge habitats for butterflies in a landscape composed of even-aged pine plantations interspersed with semi-natural habitats. Butterfly assemblages were surveyed simultaneously at the edge and the interior of 68 patches belonging to four main habitat types: herbaceous firebreaks, clearcuts and young pine stands, older pine stands, and deciduous woodlands. Butterfly species richness was higher at edges than in interior habitats, especially for pine stands. Assemblage composition differed significantly between edge and interior habitats, except for firebreaks. Of the 23 most abundant butterfly species, seven were significantly more abundant in one or all edge habitat types, five in interior habitats, and 11 species showed no edge-interior preference. Modelling the presence of individual species in edge habitats revealed the importance of habitat variables such as the abundance of nectar and host-plants, but also of the abundance of the same species in the adjacent interior habitat. Moreover, our results suggest that most species use several, different habitat types to find supplementary or complementary resources, including micro-climatic refuges to escape hot temperatures during summer. The use of adjacent edge and interior habitats by butterflies is probably a key process in such mosaic landscapes and underlines the importance of landscape heterogeneity for butterfly conservation.