Indirect evidence for an extinction debt of grassland butterflies half century after habitat loss

Habitat loss often leads to a substantial decline in species richness. However, the extinction of species is typically not instant, but rather involves a time lag. Species richness in recently disturbed habitats is therefore expected to reflect past rather than current habitat availability, with the set of species eventually going extinct representing extinction debt. We explored current species richness of butterflies (Lepidoptera: Rhopalocera) and burnet moths (Lepidoptera: Zygaenidae) with respect to past and current habitat characteristics. The study was conducted in calcareous grasslands, a habitat that has suffered a rapid decline in Europe during the last century. We showed that species richness of habitat specialists correlated positively with both past (75 years ago) and current habitat area, and was best explained by a model incorporating both of these variables. The independent effect of past habitat area presumably indicates the presence of extinction debt in the study region. Species requiring large habitat areas were more likely to show signs of extinction debt. Species richness of other grassland butterflies (those not confined to the focal habitat type) was not associated with past or current habitat area, the pattern indicating their lower sensitivity to changes in focal habitats. The response to habitat loss in specialist butterflies appears faster than in specialist plants, studied in the same landscape earlier. We conclude that linking patterns of species diversity with the temporal dynamics of habitats substantially improves the understanding of the variation in species diversity, and thus helps to identify species of conservation concern.     

Effects of anthropogenic land use on forest birds and butterflies in Subic Bay, Philippines

Despite the loss of 83% of native forests in the Philippines, little is known on the effects of this massive habitat loss and degradation on its forest biotas. This is a cause for concern because of the threat posed to the country’s large number of endemic taxa. To investigate the impacts of anthropogenic disturbance, forest birds and butterflies were surveyed in closed and open canopy forests, as well as suburban, rural and urban areas within the Subic Bay Watershed Reserve and Olongapo City in western Luzon. Measures of forest species richness and population densities for both taxa were similar in the two forest types, but showed different patterns in the other habitats. Indirect gradient analysis showed that forest bird species were positively correlated with vegetation variables (i.e., canopy cover, tree density, height to inversion and ground cover), while forest butterflies were not strongly correlated to any of the measured habitat variables. Community composition of birds in forests was distinct from those in modified habitats, while butterfly communities were more similar. A simulation showed that canopy cover of 60% or higher was required by 24 of the 26 bird species that were sensitive to canopy loss. Endemicity and nesting strata were the significant predictors of vulnerability to habitat disturbance for birds, while endemicity and larval hostplant specificity were significant for butterflies. Both taxa were negatively affected by anthropogenic disturbance but may respond to different components in the habitat (i.e., structure and resources), and thus cannot be used as surrogates of each other. Conservation of forests with contiguous canopy cover should be prioritized, and more ecological research is needed to improve the knowledge on the effects of disturbance on Philippine biodiversity.     

Effects of rainforest fragmentation on non-flying mammals of the Eastern Dorrigo Plateau, Australia

This paper describes the non-flying mammals recorded in warm-temperate rainforest fragments on the Eastern Dorrigo Plateau of New South Wales, Australia, and investigates the importance of landscape and habitat factors in determining their richness and abundance. Thirty-three rainforest fragments, ranging in size from 0.15 to 996 ha, and five sites within continuous rainforest, were surveyed. Mammal species were detected by live-trapping, spotlighting, diurnal transect walks and nest boxes. Vegetation surveys were carried out within fragments, and landscape parameters such as area and disturbance were measured on-site, via aerial photographs, and through discussion with land-owners. Nineteen species of non-flying mammals were recorded, the most common being two possums (Trichosurus vulpecula, Pseudocheirus peregrinus), a peramelid (Perameles nasuta), two native (Melomys cervinipes, Rattus fuscipes) and one introduced (Rattus rattus) species of rodent and a dasyurid (Antechinus stuartii). Mammal species richness overall was linked overwhelmingly with landscape parameters, particularly fragment area. Analyses of abundance were carried out on small mammal species only. The most important variables for A. stuartii were related to habitat, in particular structures used for nesting. Rattus fuscipes and M. cervinipes were restricted largely to fragments above 1 ha in area, and exhibited complex relationships with several habitat variables. Larger species of mammals were lost progressively from small fragments probably because their spatial requirements could not be met. Protection of existing remnants and establishment of links between these remnants and continuous forest may slow attrition of the region's mammalian fauna.     

The severe decline of butterflies on western German calcareous grasslands during the last 30 years: A conservation problem

Butterflies and burnet moths are a suitable model species group with which to analyse the general decline of invertebrate biodiversity over the last few decades. In this study, we analysed which ecological groups of butterflies and burnet moths are most affected and how the recent modifications of the landscape have influenced them. Therefore, we studied the species composition of seven calcareous grassland remnants in south-western Germany in 1972 and 2001. We observed a strong change in the community composition and a severe decline in species richness. In general, the incidence of the autochthonous non-ubiquitous species declined by more than 50%, whereas ubiquitous species showed no significant difference in numbers during this period. Especially affected by the decline were those species which need structured habitats, those which are poor dispersers, species which need habitat sizes of 16 ha and more, monophagous species, K strategists and Red Data Book species. Most probably, either habitat outside the reserves is affecting dynamics within the reserves or loss of habitat outside the protected areas has reduced the overall area and connectivity of habitat for some species, increasing extinction rates and reducing colonisation rates in metapopulations. We conclude that these negative trends can only be stopped or even reversed if the landscape structure is made less hostile for species with conservation interest.     

Restoring grassland biodiversity: Sowing low-diversity seed mixtures can lead to rapid favourable changes

We studied the effect of sowing low-diversity seed mixtures (containing 2-3 competitive grass species) on the regeneration of vegetation on croplands previously used as alfalfa fields. In four permanent plots in 10 restored fields (four with alkali and six with loess seed mixture) the cover of flowering plants was recorded and phytomass was measured between 2006 and 2008. We asked three questions: (i) How fast will weedy, short-lived species decrease in abundance during secondary succession enhanced by sowing low-diversity seed mixtures? (ii) Can weeds be suppressed by sowing competitive native grasses, followed up by management by mowing? (iii) Can succession towards the target native grasslands be accelerated by sowing only low-diversity seed mixtures compared to set-aside old field succession? Our results showed that in just two years a vegetation dominated by perennial grasses has developed, which successfully prevented the establishment of weed species. These results suggested that sowing seeds of two or three competitive grass species is an effective tool to eliminate weed domination and to lead towards the restoration of species poor grasslands with grass domination such as alkali grasslands. However, the developed dense perennial grass cover and the accumulated litter may hamper the immigration of specialist species characteristic to reference grasslands. Therefore, the restoration of species-rich grasslands requires the facilitation of the immigration of grassland specialist species by further management (grazing, mowing and/or hay-transport).     

Effects of soil properties and land management on the structure of grassland snail assemblages in SW Germany

Quantitative analyses of the snail assemblages of four a priori defined categories of grassland sites, characterized by soil moisture, land use and management, were conducted in SW Germany. Topsoil pH and calcium content were determined for each of 39 sites. The objectives were to study the effects of these habitat characteristics on snail density, species richness and quantitative structure of the land snail assemblages. With one exception, no significant relationships between soil pH (as a proxy for Ca supply) and the total numbers of individuals and species at the four site categories were observed. Snail density and species richness on groundwater soils, represented by rarely mown sedge stands and regularly mown meadows, were clearly higher than on intermediate moisture soils (as defined by the climatic water balance) of regularly mown meadows, indicating that soil moisture was the most important factor accounting for these differences. Furthermore, we observed specific conditions associated with the presence of trees in the category of meadow orchards on intermediate moisture soils. There, numbers of individuals and species were significantly higher than in the meadows on intermediate moisture soils. A posteriori cluster analysis of quantitative similarity of all snail assemblages showed that soil moisture accounts for the major differences between the site categories with respect to snail density, species richness and quantitative composition of the grassland snail assemblages. As these results are in contrast to the findings of many woodland studies, we suggest that the occurrence or abundance of certain species in the site categories are explained by land management, especially by frequent disturbances at the soil surface caused by mowing.     

Old cultural traditions, in addition to land use and topography, are shaping plant diversity of grasslands in the Alps

Socio-economically motivated land use changes are a major threat for species diversity of grasslands throughout the world. Here, we comprehensively explore how plant species diversity of grasslands in the species-rich cultural landscape of the Swiss Alps depends on recent land use changes, and, neglected in previous studies, on old cultural traditions. We studied diversity in 216 grassland parcels at three altitudinal levels in 12 villages of three cultural traditions (Romanic, Germanic, and Walser). In valleys of Romanic villages more different parcel types tended to occur than in those of Germanic and Walser villages, suggesting that socio-economic differences among cultural traditions still play a role in shaping landscape diversity. Moreover, at the village level, higher man-made landscape diversity was associated with higher plant species richness. All observed changes in land use reduced the farmers’ workload. Plant species richness was lower in fertilized than in unfertilized parcels and in abandoned compared with used parcels. Grazing slightly reduced species richness compared with mowing among unfertilized parcels, while in fertilized parcels it had a positive influence. The highest species diversity was found in mown unfertilized subalpine grasslands. Nevertheless, moderate grazing of former meadows can be a valuable alternative to abandonment. We conclude that the ongoing changes in land use reduce plant species richness within parcels and at the landscape level. To preserve plant species diversity at the landscape level a high diversity of land use types has to be maintained.     

Effects of crop abandonment and grazing exclusion on available soil water and other soil properties in a semi-arid Mongolian grassland

Improper cropping and overgrazing have led to land degradation in semi-arid regions, resulting in desertification. During desertification, vegetation changes have been widely observed, and are likely controlled to some extent by soil water. The purpose of this study was to investigate changes in soil physical properties, organic C, and vegetation induced by land-use changes, with special reference to the dynamics of available soil water. We selected four study sites in a typical Mongolian steppe grassland: grassland protected from grazing, grazed grassland, abandoned cropland, and cultivated cropland. Grazing exclusion increased the cover of perennial grass, with little increase in the root weight. Since there was no difference in available water between the grasslands with and without grazing, there appears to be no serious soil compaction due to overgrazing. On the other hand, vegetation cover and the number of species were poor in both abandoned cropland and cultivated cropland. However, the root weight was greater in abandoned cropland. Although the abandonment of cultivation appeared to increase organic C, available water did not differ significantly in comparison with cultivated cropland. The silt contents were significantly lower in abandoned and cultivated cropland than in both grasslands, suggesting the effects of wind erosion. In addition, the silt contents were positively correlated with the volume fraction of storage pores for available water. Therefore, the lower silt contents may constrain the volume of available water in abandoned cropland. Moreover, the unsaturated hydraulic conductivity results indicated that the diameters of storage pores for available water at the present study sites were smaller than those suggested by previous studies. Although the differences in vegetation cover by different land-use types were observed at every site, differences in the volume of available water were observed at between abandoned cropland and cultivated cropland. The reason why the no differences in available water between grazed grassland and grasslands protected from grazing may be short time of grazing exclusion for 2 years for evaluating the effects of exclusion on soil properties.     

The relationship between local extinctions of grassland butterflies and increased soil nitrogen levels

In contrast to many other western European countries, the knowledge about trends in the Swedish butterfly fauna is poor. We studied the effects of habitat and species characteristics on species turnover in 13 grassland sites in southern Sweden by comparing species richness and compositions at two separate occasions with an interval of 21 years. The mean number of species per site decreased from 30 to 24, with a large variation between sites. The number of extinctions was highest in sites where the proportion of trees and shrubs had increased most, but there was no detectable effect of area or of the composition of landscapes surrounding the sites. Areas protected as nature reserves had lost as many species as unprotected areas had, indicating both the importance of proper management of nature reserves and that nature reserves alone may not be enough to inhibit regional extinction of butterfly species. Species dependent on nutrient-poor conditions tended to decrease while species dependent on nutrient-rich conditions tended to increase, indicating a negative effect of increased soil nitrogen levels resulting from active fertilizing of pastures and/or atmospheric nitrogen deposition. A regular monitoring program could show whether our results are representative for Sweden or Northern Europe.     

Small mammals in agricultural landscapes of Prince Edward Island (Canada): Effects of habitat characteristics at three different spatial scales

We examined the influence of habitat characteristics at the microhabitat, macrohabitat, and landscape spatial scales on small mammals occurring in 12 forest patches within four agricultural landscapes of Prince Edward Island (Canada). Landscape features were important determinants of small mammal variables at all levels, but especially at the community level, whereas microhabitat characteristics tended to influence small mammals at the population level. Macrohabitat characteristics had only minor effects on small mammals occurring in our study sites. Species richness was most strongly influenced by patch area, reaching a threshold at forest patches of roughly 8-10 ha. The proportions of both forest and hedgerow cover within 400 m from the study site were also significant determinants of small mammals species diversity, possibly reflecting their ability to perceive suitable habitats, forage in areas outside the forest patches, and/or disperse in agricultural landscapes. At least one small mammal species (Napaeozapus insignis) benefitted from the presence of agricultural fields at distances up to 1000 m. Tamias striatus benefitted from the presence of hedgerow cover within 400 m from forest patches, possibly allowing them to move between forest patches. Clearly, the maintenance of forest patches of 8-10 ha and of forest cover within 400 m from them is fundamental for the conservation of small mammals inhabiting agricultural landscapes on the Island. Conservation strategies should also consider the establishment of more effective regulations to prevent and/or reduce hedgerow removal on Prince Edward Island.     

Habitat use and conservation of bumblebees (Bombus spp.) under different grassland management regimes

Declines in the natural populations of several bumblebee species across Britain and Europe are an increasing cause for concern. In this study the habitat use of bumblebees was investigated on Salisbury Plain Training Area, the largest remaining area of unimproved chalk grassland in north-west Europe. Habitat characteristics influencing the overall abundance, species richness and foraging activity of bumblebees included the diversity and abundance of flowering plant species (particularly of favoured forage plants such as Trifolium pratense), vegetation structure and height. It is suggested that different Bombus species respond to these habitat characteristics depending on their specific foraging and nesting requirements, the case of Bombus humilis being especially relevant. The effects of several grassland management practices were considered in terms of their suitability for the conservation of bumblebee habitats. Cattle grazing was shown to be preferable to both sheep grazing and the absence of any management, although the timing and intensity of such grazing was important. Small-scale disturbances caused by vehicle activity were also of value in producing locally abundant forage resources in less intensively managed grasslands.     

A biodiversity monitoring framework for practical conservation of grasslands and shrublands

Comprehensive and standardized biodiversity monitoring schemes are needed to build scientifically sound decision-making tools for biodiversity conservation. Based on a thorough review of published literature, we propose a novel biodiversity monitoring framework to unify conservation theory and practice. The framework is built on the inter-connection among different types of indicators, and on the systematic articulation of their relationships into seven indicator approaches. Semi-natural grasslands and shrublands in Europe, which still lack a common biodiversity monitoring scheme, are used as a model for the framework. Different biotic indicators have been widely used to estimate the state of biodiversity, but we integrate these with biodiversity drivers, i.e. factors driving changes in biodiversity, to track biodiversity response to environmental changes. Precise information on biodiversity drivers (e.g. past and present management or disturbance regimes, environmental conditions, landscape patterns) has an effective indicator value, but this is often not taken into account in monitoring schemes. Our framework can be used to detect gaps in available data, translate indicator systems into practical conservation, identify combined sets of indicators to monitor biodiversity in target habitats, and recognize most suitable surrogates when information for some indicators is missing. We also take into account the effect of regional species pools in order to consider large-scale historical and biogeographical processes. We propose general guidelines to create validate and launch biodiversity monitoring frameworks for target habitats in the light of current examples of biodiversity conservation schemes (e.g. Natura 2000 in Europe).     

太行山区不同农业景观生境的蜘蛛群落结构特征及其影响因子

为探索太行山区农业景观中不同生境类型对蜘蛛多样性的影响,采用陷阱法对河北省武安市西部太行山区5种类型生境(核桃林、玉米地、苹果-芍药套作园、次生林、绿海花廊景观带)的地表蜘蛛多样性进行调查。通过分析5种类型生境中蜘蛛多样性分布及其与局部生境因子的相关关系,探讨半自然生境对蜘蛛的保护作用。结果表明:人为干扰会显著降低生境中蜘蛛丰富度和多度;增加植被群落结构的复杂程度会使生境中蜘蛛丰富度显著增加,而蜘蛛的多度显著降低;蜘蛛的多度随生境中枯落物厚度的增加而增加。其中核桃林的蜘蛛Shannon-Wiener多样性显著高于其他4种类型生境,核桃林、次生林和绿海花廊的蜘蛛丰富度显著高于苹果-芍药套作园和玉米地,苹果-芍药套作园和绿海花廊的蜘蛛多度显著高于其他3种生境。玉米地、苹果园-芍药套作和绿海花廊中蜘蛛的群落组成具有较高相似性,而核桃林与次生林中蜘蛛群落结构具有较高异质性。地表枯落物厚度是影响当地蜘蛛群落结构的最主要因素。研究区在农业景观与自然景观的过渡区种植核桃林、苹果-芍药套作园和绿海花廊间作板栗,对蜘蛛多样性的保护都有积极作用;不同的生境因子与不同蜘蛛群落的关系不同,如狼蛛偏向人为干扰较大的苹果-芍药套作园和绿海花廊景观带,所以生产管理时要结合特有的生境条件,对相应的蜘蛛进行合理的保护和高效的利用。研究结果对当地的农业景观生境管理和生物多样性保护具有指导意义。     

Responses of birds of different biogeographic origins and habitat requirements to agricultural land abandonment in northern Spain

Agricultural land-use changes in Europe have taken two opposing directions: towards agricultural intensification or land abandonment. While in the Mediterranean region land abandonment is a main cause of avian diversity decline, in northern Europe species diversity often increases with successional age. We examined the hypothesis that the biogeographic origin of the avifauna determines whether abandonment brings conservation benefits or detriment by studying the bird community of agricultural land in northern Spain, at the boundary of the Mediterranean and Eurosiberian regions. Using a successional gradient, we examined landscape-scale effects of agricultural abandonment on birds during the breeding and non-breeding seasons.The trend in avian diversity with successional stage differed little between Mediterranean and Eurosiberian species in winter. In the spring, however, there was an increase in diversity with stage in abandonment for Eurosiberian birds but not for Mediterranean species. Analysis of individual species showed a preference among Eurosiberian birds for more wooded habitats whereas Mediterranean birds preferred open areas and shrubland.The introduction of agricultural policies to geo-political units that do not coincide with eco-regions cannot be assumed to bring uniform conservation benefits. In the Mediterranean region, agricultural mosaics of low intensity cultivation maintain the highest diversity of priority bird species. Agricultural land abandonment should not be assumed to benefit conservation.     

Detection of extinction debt depends on scale and specialisation

Many plants can persist in landscapes for a long time after focal habitats have disappeared or become fragmented, which might contribute to an extinction debt. Delayed responses of plant occurrence have recently received great attention, particularly in conservation, although evidence for extinction debts is incongruent. Here we asked if we could detect an extinction debt for plant species after 100 years of fragmentation, depending on regional or local (gamma or alpha respectively) diversity measure used, and if all plant species or only habitat specialists were investigated. Historical and contemporary grassland patterns were analysed in 33 rural landscapes (each 1 km² in diameter) in south-eastern Sweden. Results show that managed semi-natural grassland had declined from 39% to 3% in 100 years. Diversity measured at regional scale was best explained by grassland extent 100 years ago, for both all species and grassland specialists. Present-day management, but neither present nor past grassland extent, was important for grassland specialists’ occurrence at the local scale, although present-day grassland proportion had a positive influence on species richness at the local scale. We found evidence of an extinction debt at both local and regional scale when all species were included in the analysis, but not for grassland specialist species at the local scale. However, the extinction debt is still to be settled for grassland specialists at the regional scale, and therefore the estimation of extinction debts in fragmented habitats presents one of the greatest challenges for conservation today and in the future.     

The influence of plant diversity on people’s perception and aesthetic appreciation of grassland vegetation

The conservation of biodiversity critically depends on the value that humans attach to it. Apart from an ecological and economic value, an aesthetic value has often been assigned to biodiversity. However, it is not known whether lay people appreciate the diversity of species and not just certain individual species or nature as a whole. We studied in a series of experiments and field studies people’s perception and appreciation of species diversity. We presented meadow-like arrays of different species richness and evenness but random species composition to lay people and asked them to estimate plant species richness and rank the arrays by attractiveness. The experiments were complemented by two larger-scale field studies using natural meadows. Both in the experiments and the field studies the mean perception of species richness by people increased with true species richness, but was slightly overestimated at low and increasingly underestimated at high diversity levels. Lay people’s aesthetic appreciation of both the experimental grassland arrays and the natural meadows increased with true species richness. Communities consisting of the same number of species were perceived to be more species-rich and were appreciated more when their evenness was high. Our results demonstrate that plant diversity in itself is attractive to humans. The current reduction of the diversity of grasslands due to intensification of management may thus reduce the attractiveness of regions where grasslands are a dominant feature of the landscape. This could have negative consequences for tourism and may add an economic argument for the conservation of biodiversity in grasslands.     

Historical impacts on linear habitats: The present distribution of grassland species in forest-edge vegetation

In highly fragmented agricultural landscapes, abandoned forests and dense coniferous plantations established on former semi-natural grassland remain potentially suitable sites for the restoration of grassland communities. The roadside vegetation along the edges of these remnant forests could be a key landscape component, because these communities retain pools of grassland species that are maintained by regular mowing alongside public roads to improve traffic safety. We evaluated the effect of land-use history and the proportion of suitable surrounding habitats on the present distribution of grassland species in roadside forest-edge vegetation. The average number of grassland species was significantly lower at sites that had been cultivated since the 1950s, but it did not differ between uncultivated sites and sites cultivated during the 1880s. Positive effects of the proportion of suitable habitats around the sites were detected at specific spatial scales (500- and 700-m squares), and these effects were indistinct at sites that had lost populations to cultivation. In addition to the present habitat conditions (e.g., forest type), the best-fit model for explaining the present distribution of grassland species at a site included both the site’s land-use history and the past proportion of suitable habitat around the sites. Even in remnant linear habitats such as forest-edge vegetation along roads, historical patterns of site conditions and the landscape matrix at optimum scales can provide useful knowledge to improve explanations of the present distributions of grassland species. These information can help identify abandoned or planted forest sites potentially suitable for restoration with grassland species.     

宁南山区草地植被恢复方式对土壤饱和导水率的影响

为评价宁南山区草地植被不同恢复方式对土壤入渗性能的影响,以不同植被群落的饱和导水率为研究对象,采用逐步回归研究退耕农地、禁牧荒地、封育草地导水率的变化及影响因子,并探讨了其作用机制。结果表明：3种植被恢复方式均有利于0-40 cm土壤饱和导水性能提高;各土层土壤饱和导水率均随植被恢复而不断提高,0-5 cm土层改善作用最为明显;农地退耕序列和荒地禁牧序列5-40 cm土层、封育草地序列0-40 cm土层土壤饱和导水率随土层深度下降而降低;影响土壤饱和导水率的因子为土壤有机质因子和土壤结构因子;3种植被恢复方式土壤有机质质量分数与Ks均呈显著的线性相关关系,在该区域有机质质量分数越高,Ks增加越快;土壤有机质积累是土壤饱和导水率提高的根本动力。因此,草地封育更利于提高使该地区土壤导水性能提高,促进生态恢复。     

Patterns of species diversity in rural herbaceous communities under different management regimes, Chiba, central Japan

The patterns of plant species diversity in herbaceous vegetation subjected to various human activities were studied in most of the landscape elements in a rural area of Chiba, central Japan. Twenty-eight transects were sampled in four types of human management-regime (cultivation, trampling, mowing, and abandonment) and were grouped into seven vegetation types using TWINSPAN and DCA analyses. The DCA axis 1 arranged all the transects into a successional order along which biomass and the degree of succession increased. Accumulated number of species increased in a stepwise pattern along the DCA axis 1, in which the dominant plant life-forms were replaced from annuals, to perennials and perennials/tree-saplings depending on different management regimes. The unique species which were confined to a certain management regime, were identified in each site. It is suggested that the coexistence of various successional communities under different human management regimes enhance regional species diversity through maintaining these unique species. Among four types of management regime, mowing sites (especially traditional verge meadows) had most abundant unique, rare species specially adapted to regular cutting. It is suggested that maintaining such traditional mown sites is important to conserve the unique biodiversity of the studied area.