Grassland Connectivity Research Articles

Small grassland fragments and connectivity support high arthropod functional diversity in highly modified landscapes

Abstract Grassland ecosystems undergo dramatic habitat loss and fragmentation worldwide due to agricultural expansion and intensification. Among different taxonomic groups, grassland arthropods are particularly sensitive to this process and, therefore, are exposed to considerable risk. Although many studies focus on land use impacts on arthropod diversity, these mostly consider taxonomic diversity and neglect trait‐mediated functional responses. However, studying functional diversity often provides more accurate insights into ecosystem processes. Here, we assessed the effect of fragment size and connectivity on the functional composition (community‐weighted mean trait values) and diversity (Rao's quadratic entropy) of two diverse and abundant arthropod groups: spiders and true bugs. We assigned functional traits for more than 300 species collected from 30 sandy steppe (forest‐steppes) and 30 loess steppe fragments (kurgans) in the southern part of the Hungarian Great Plain. Functional responses to fragmentation were observed for spiders in forest‐steppes and for true bugs in kurgans. We found higher functional diversity in better‐connected fragments for spiders and in small fragments for both groups. We collected small, humidity‐preferring and web‐building spiders in small fragments, and there were more ballooning spiders with moist habitat preferences in well‐connected fragments. Furthermore, increasing grassland connectivity resulted in a significantly higher proportion of polyphagous and humidity‐preferring individuals in the true bug communities. Our results highlight the importance of small grassland fragments in maintaining high arthropod functional diversity. Even small fragments in a well‐connected grassland network can promote ecosystem functioning and associated services within human‐dominated landscapes.

Dynamic simulation of functional connectivity and identification of conservation priorities for grassland in China’s Poyang Lake considering ecological processes

Analysing dynamics of landscape functional connectivity and evaluating conservation priority of habitat patches are of great significance for biodiversity conservation. Taking the grassland of Poyang Lake as a case, and comprehensively considering the ecological processes of water level change and species dispersal, this study firstly identified the range and patch composition of grassland under different water levels. Then, the graph theoretical approach was applied to analyse the dynamics of functional connectivity of grassland with different water levels and dispersal distances. Finally, the delta value for probability of connectivity (dPC) and betweenness connectivity (BC) were respectively used to identify the most important grassland patches and key grassland nodes. The results showed as follows: (1) The grassland presented the characteristics of “expanding when water falls while shrinking when water rises”. The grassland patches faced both the segmentation effect and the inundation effect of water. With the increase of water level, the distribution of grassland was gradually shrinking, the distribution of grassland decreased from 1813.61 km2 at the water level of 7.54 m to 182.36 km2 at the water level of 17.17 m, and the fragmentation of large patches and the disappearance of small patches coexisted. (2) From the perspective of water level change, the functional connectivity of grassland has progressively decreased with the increase of water level. From the perspective of species dispersal, the species dispersal distance had an absolutely positive impact on landscape functional connectivity. With the increase of dispersal distance, the functional connectivity of grassland increased dramatically. (3) The 124 important grassland patches were identified and mapped. They were all larger ones in area and primarily distributed in the center of Poyang Lake, especially concentrated in the two national nature reserves. The 16 key grassland nodes were determined and mapped. They were very small in size and mainly scattered in the central and southern margin of Poyang Lake. Giant patches and large patches play an extremely vital role in maintaining the grassland connectivity. However, small patches in pivotal locations can not be ignored as stepping stones or connecting elements. Our study provides a scientific reference for the protection and management of natural habitats in lake areas.

Dynamic simulation of the grassland connectivity and the effects of landscape pattern in China's Poyang Lake from the integrated perspective of habitat and biology

AbstractAnalysing the dynamics of landscape connectivity is of great significance for biodiversity conservation, but the scientific expression of ecological processes and the depth of coupling landscape pattern and ecological process requires to be strengthened. Taking the grassland of Poyang Lake as a case, based on the integrated perspective of habitat and biology, and comprehensively considering the ecological process of water level change and species dispersal, this study firstly analysed the changes of functional connectivity of grassland with different water levels and dispersal distances by using the graph‐based connectivity indices. Then, landscape pattern indices were applied to analyse the dynamics of landscape pattern of grassland and further study the effects of landscape pattern on landscape functional connectivity. The results showed as follows: (1) From the perspective of habitat, the functional connectivity of grassland has progressively decreased with the increase of water level. From the perspective of ecology, the species dispersal distance had an absolutely positive impact on landscape functional connectivity. With the increase of dispersal distance, the functional connectivity of grassland increased significantly. (2) The dynamics of landscape pattern of grassland showed that with the increase of water level, the patch area shrank, the patch shape tended to be simple, the patch density decreased and the patch fragmentation aggravated. (3) The correlation results between landscape pattern and functional connectivity indicated that flux index (F) had a significant positive relationship with patch density (PD), edge density (ED), probability of connectivity (PC) had a strong significant positive relationship with largest patch index (LPI), COHESION and number of components (NC) had a negative relationship with LPI, ED, COHESION. This study provides theoretical guidance for the protection and management of grassland in Poyang Lake.

The contribution of roadsides to connect grassland habitat patches for butterflies in landscapes of contrasting permeability

Roadsides, in particular those being species-rich and of conservation value, are considered to improve landscape permeability by providing corridors among habitat patches and by facilitating species' dispersal. However, little is known about the potential connectivity offered by such high-value roadsides. Using circuit theory, we modelled connectivity provided by high-value roadsides in landscapes with low or high permeability in south-central Sweden, with ‘permeability’ being measured by the area of semi-natural grasslands. We modelled structural connectivity and, for habitat generalists and specialists, potential functional connectivity focusing on butterflies. We further assessed in which landscapes grassland connectivity is best enhanced through measures for expanding the area of high-value roadsides. Structural connectivity provided by high-value roadsides resulted in similar patterns to those of a functional approach, in which we modelled habitat generalists. In landscapes with low permeability, all target species showed higher movements within compared to between grasslands using high-value roadsides. In landscapes with high permeability, grassland generalists and specialists showed the same patterns, whereas for habitat generalists, connectivity provided by high-value roadsides and grasslands was similar. Increasing the ratio of high-value roadsides can thus enhance structural and functional connectivity in landscapes with low permeability. In contrast, in landscapes with high permeability, roadsides only supported movement of specialised species. Continuous segments of high-value roadsides are most efficient to increase connectivity for specialists, whereas generalists can utilize also short segments of high-value roadsides acting as stepping-stones. Thus, land management should focus on the preservation and restoration of existing semi-natural grasslands. Management for enhancing grassland connectivity through high-value roadsides should aim at maintaining and creating high-value roadside vegetation, preferably in long continuous segments, especially in landscapes with low permeability.

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

A decrease in habitat amount and connectivity causes immediate or delayed species extinctions in transformed landscapes due to reduced functional connections among populations and altered environmental conditions. We assessed the effects of present and historical grassland amount and connectivity as well as local habitat factors typical of the present landscape on the current species richness of grassland specialist and generalist plants and arthropods in grassland fragments. We surveyed herbaceous plants, ants, orthopterans, true bugs and rove beetles in 60 dry grassland fragments in Hungary. We recorded the area of the focal grassland, the slope and the cover of woody vegetation. By using habitat maps of the present and historical landscape, we calculated grassland amount and connectivity for four time periods covering 158 years (1858–2016). We found evidence for an unpaid extinction debt in specialist plants, suggesting that they have not come to equilibrium with the grassland amount and connectivity of the present landscape yet. This localised and typically long-lived group responded slowly to the landscape changes. Specialist arthropod taxa with short generation times responded much faster to habitat loss than plants and did not show an extinction debt. Generalist plants and animals adapted to a wide range of habitats were affected by the landscape-scale decline of grassland habitats. Despite decreased habitat connectivity, grassland fragments with dry environmental conditions and high environmental heterogeneity can sustain specialist plants in transformed landscapes. Unpaid extinction debt should be considered an early warning signal: Restoration of grassland connectivity is necessary to halt ongoing extinction processes.

Habitat availability and climate warming drive changes in the distribution of grassland grasshoppers

Land use and climate change are considered the major drivers of current insect declines. However, in intensively used agricultural landscapes the impacts of both on Orthoptera (hereinafter termed ‘grasshoppers’) are still poorly understood. We analysed grasshopper assemblages in two grassland types (patches, N = 63 and verges, N = 118) by comparing two surveys – one in 1995 and one in 2012 – in an agricultural landscape of the NW-German Lowland. Despite the short time period between the two surveys, we detected strong changes in environmental conditions and grasshopper assemblages. In contrast to grassland verges, grassland patches suffered from severe habitat loss. More than a quarter of all grassland patches were converted to other biotope types, in particular, arable fields cropped with maize. Additionally, summer temperatures rose by 1.1 °C. Species richness and the Community Temperature Index also increased in grassland patches and verges. By contrast, the Community Farmland Index decreased. The ongoing cultivation of maize as a bioenergy crop was responsible for a severe loss of grassland patches leading to a homogenization at the landscape level. However, due to the high connectivity of grasslands, thermophilous and generalistic grasshopper species with both low and high dispersal ability were able to track global warming. Based on our study, (i) the availability of suitable habitats and (ii) climate warming were the major drivers of grasshopper assemblage shifts. With the ongoing loss of grassland patches, grassland verges become increasingly important not only as dispersal corridors, but also as refuges for biodiversity.

Agri‐environment conservation set‐asides have co‐benefits for connectivity

Widespread declines in farmland biodiversity have led to state‐funded schemes which take land out of production to create (semi‐)natural habitats for biodiversity (e.g. EU agri‐environment schemes; US Conservation Reserve Program). Common features of such schemes are grassland strips at the edges of agricultural fields, and we examine potential co‐benefits of these biodiversity set‐asides for contributing to grassland connectivity. Although set‐aside strips had negligible impact on landscape‐scale species persistence (using metapopulation models parameterized for flying insects run on 267 landscapes of ~30 000 ha across England), they nonetheless improved connectivity in 74% (198/267) of landscapes (comparing landscapes with and without set‐asides), as shown by range expansion rates increasing by up to 100%. Benefits of set‐aside strips varied according to species type (high/low dispersal, high/low population density), but had little benefit for species with low dispersal and small population sizes, which generally failed to expand. High dispersal/high density species were already successful expanders regardless of set‐asides (> 75% of simulations were successful without set‐asides) although expansion rates were still improved when set‐asides were added. Whilst alternative strategies for placement of set‐aside strips (more/less aggregated), revealed no consensus ‘better’ strategy across species types, set‐aside benefits were generally greatest in landscapes with intermediate availability of semi‐natural grassland (0.5‐4% cover). We conclude that small‐scale set‐asides have the potential to improve connectivity, which we expect to help some species track climate change, and connect habitat patches within existing climate space for others. However, set‐asides are unlikely to benefit low dispersal species which are probably at greatest risk from agricultural intensification.

Disentangling the effects of host resources, local, and landscape variables on the occurrence pattern of the dusky large blue butterfly (Phengaris nausithous) in upland grasslands

Determining the effects of local and landscape drivers on endangered species and predicting potential suitable habitats for their persistence is crucial for effective conservation management. Here, we applied a multi-scale approach to disentangle the effects of host resources, local, and landscape variables on the occurrence pattern of Phengaris (= Maculinea) nausithous in semi-natural upland grasslands. Our approach comprised the assessment of host parameters (plant cover, density, height, flower heads density, ant nest density, ant colony size), local grassland management (pasture, meadow), site conditions (area, shape, terrain attributes), and landscape variables (landscape composition, connectivity). We used ensemble of small models based on bivariate generalized linear models for explaining and predicting the butterfly occurrence pattern. Bivariate models revealed that host ant nest density, plant cover and height, local grassland management type (pasture), slope and eastness, landscape forest cover and grassland connectivity had a positive effect on the occurrence of P. nausithous (average explained deviance 20.5%). Host ant density, host plant cover, and local grassland management were the most influential factors on the ensemble predictions. The presence of P. nausithous in upland grasslands is not only determined by host resources, but also by local and landscape factors. Such factors proved to be relevant for identifying and predicting suitable grassland sites for this endangered species. Consequently, we recommend that conservation actions should include a landscape perspective to promote connectivity by facilitating coherent grazing networks enabling dispersal between semi-natural upland grasslands and thus species persistence.

Disturbance has benefits as well as costs for fragmented populations of a cryptic grassland reptile

Conservation practitioners face complex decisions about the management of spatial and temporal disturbance regimes when disturbance plays a significant role in the dynamics of fragmented populations. This is particularly so if disturbance events have negative short-term consequences but are necessary for maintaining habitat quality in the longer term. We sought to determine the potentially interactive effects of two disturbance processes (fire and grazing) on the occupancy dynamics of the threatened Striped Legless Lizard (Delma impar) among native grassland fragments in Victoria, Australia. We collected 9 years of occupancy data from 291 sites. We used these data to examine the influence of disturbance frequency and coincidence on rates of occupancy and persistence, plus the influence of grassland connectivity on colonisation rates. Fire and grazing were positively related to the persistence of D. impar populations at the frequencies observed during this study, but the interaction of these two disturbances had a strong negative effect on persistence. Colonisation of grassland fragments was positively related to connectivity to grassland habitat in the surrounding landscape. Strategic use of fire and grazing to manage fragmented grasslands can be beneficial for the persistence of D. impar populations, but intense and concurrent application of both these disturbances may trigger population collapse. Conservation risks of inappropriate disturbance are highest in small, isolated fragments of grassland, where recolonisation is unlikely. More broadly, our study highlights the value of coupling long-term occupancy and management data to investigate the influence of disturbance processes on population persistence in fragmented landscapes.

Connectedness of habitat fragments boosts conservation benefits for butterflies, but only in landscapes with little cropland

Global change pressures (GCPs) imperil species and associated ecosystem functions, but studies investigating interactions of landscape-scale pressures remain scarce. Loss of species-rich habitat and agricultural expansion are major threats for biodiversity, but if or how these factors interactively determine community-level shifts and conservation outcomes remains unclear. We tested whether matrix simplification (dominance of cropland) and reduced connectivity (i.e. landscape-scale habitat loss) either additively, synergistically or antagonistically cause community shifts in butterflies, a group of high conservation relevance. We surveyed butterflies on 30 small calcareous grassland fragments (< 1 ha) in Central Germany, representing independent gradients in grassland connectivity (an index combining grassland area and proximity), and matrix quality (landscape proportion of cropland). Using proportional odds logistic regression, we assessed whether connectivity and matrix quality interactively altered the distribution of Red List statuses, and assessed effects of local scale management (mowing, grazing, short-term abandonment). We found synergistic, conservation relevant effects: Connectivity boosted the proportion of red-listed species from 20 to 52% in crop land poor landscapes, but not in crop land rich landscapes, particularly driven by endangered and critically endangered species. Grazed sites had the lowest species richness, abundance, and proportions of conservation relevant butterflies. Mitigation measures targeting one landscape-scale pressure only may be inefficient, particularly for red-listed species. Increasing habitat connectivity bolsters butterfly communities and potential pollination services, but only if accompanied by measures to soften the matrix. Hence, halting biodiversity losses needs better understanding and implementation of complex conservation measures at the landscape scale.

Incorporating landscape heterogeneity into multi-objective spatial planning improves biodiversity conservation of semi-natural grasslands

Recent actions to mitigate biodiversity loss in agricultural environments appear insufficient despite the considerable efforts channeled via the European Union’s Common Agricultural Policy. One likely reason for this failure is the limited attention paid to the regional and landscape level ecological characteristics in farmland conservation planning. We demonstrate how to obtain conservation prioritization solutions that would address simultaneously three goals, including two landscape level targets: minimizing local habitat quality loss, maximizing habitat connectivity, and incorporating landscape heterogeneity. As these goals may be contradictory, we investigate the potential trade-offs between them. We used the Zonation prioritization tool to examine how our three goals could be implemented in the agricultural landscapes of southwest Finland. We used measures of (i) biodiversity value of grasslands, (ii) connectivity between grasslands, and (iii) landscape heterogeneity which comprised of (land cover type based) compositional heterogeneity and (field margin based) configurational heterogeneity. Integration of landscape heterogeneity measures and habitat connectivity resulted in some trade-offs with local habitat quality, the most prominent observation being that landscape heterogeneity co-varied with grassland connectivity. Among the two landscape heterogeneity parameters, inclusion of compositional heterogeneity resulted in more clustered prioritization solutions than configurational heterogeneity, which had a spatially more balanced impact. Concordance among landscape scale factors implies high potential for reconstruction of a functioning network of semi-natural grasslands in areas under intensive agricultural use. Broader scale multi-objective planning approaches can thus importantly support targeting biodiversity conservation planning and mediating the implementation of Common Agricultural Policy objectives.

Adjacent woodlands rather than habitat connectivity influence grassland plant, carabid and bird assemblages in farmland landscapes

One response to biodiversity decline is the defnition of ecological networks that extend beyond protected areas and promote connectivity in human-dominated landscapes. In farmland, landscape ecological research has focused more on wooded than open habitat networks. In our study, we assessed the infuence of permanent grassland connectivity, described by grassland amount and spatial confguration, on grassland biodiversity. We selected permanent grasslands in livestock farming areas of north-western France, which were sampled for plants, carabids and birds. At two spatial scales we tested the efects of amount and confguration of grasslands, wooded habitats and crops on richness and abundance of total assemblages and species ecological groups. Grassland connectivity had no signifcant efects on total richness or abundance of any taxonomic group, regardless of habitat afnity or dispersal ability. The amount of wooded habitat and length of wooded edges at the 200 m scale positively infuenced forest and generalist animal groups as well as grassland plant species, in particular animal-dispersed species. However, for animal groups such as open habitat carabids or farmland bird specialists, the same wooded habitats negatively infuenced richness and abundance at the 500 m scale. The scale and direction of biodiversity responses to landscape context were therefore similar among taxonomic groups, but opposite for habitat afnity groups. We conclude that while grassland connectivity is unlikely to contribute positively to biodiversity, increasing or maintaining wooded elements near grasslands would be a worthwhile conservation goal. However, the requirements of open farmland animal species groups must be considered, for which such action may be deleterious.

Grassland connectivity in fragmented agricultural landscapes of the north-central United States

In the prairies of North America, remnant native grasslands are threatened by continuing agricultural extensification. Fragmentation of the remaining grassland isolates patches and limits the potential for dispersal of native species. We explored these impacts by analyzing the spatial pattern of native grassland habitats in the Prairie Coteau region of eastern South Dakota and western Minnesota, USA. Undisturbed grasslands were mapped using a GIS database of land use history combined with manual interpretation of high-resolution aerial photographs. Network analysis based on graph theory was used to examine how connectivity changed depending on the potential movement distances of organisms and to identify important patches that made large contributions to connectivity throughout the broader network. Interpatch movement was assessed using Euclidian distance as well as cost-weighted distance that assigned lower movement cost to grasslands than to human-modified land cover types. Much of the undisturbed grassland was concentrated in a single large cluster, which was connected to other habitat concentrations via corridors of “stepping stone” patches. A small number of “keystone patches”, whose loss would have a disproportionately large effect on overall connectivity, were also identified. The locations of the major corridors were relatively consistent across different movement distances. Information about patch-level importance for overall network connectivity should be taken into account when prioritizing conservation and restoration. Future studies can build on this research by conducting more detailed assessments focused on particular species of concern and portions of the study area where connectivity is most limited.

Contrasting habitat and landscape effects on the fitness of a long‐lived grassland plant under forest encroachment: Do they provide evidence for extinction debt?

AbstractHabitat loss, fragmentation and transformation threaten the persistence of many species world‐wide. Population and individual fitness are often compromised in small, degraded and isolated habitats, but extinction can be a slow process and extinction debts are common.Long‐lived species are prone to persist as remnant populations in low‐quality habitats for a long time, but the population‐ and individual‐level mechanisms of extinction debt remain poorly explored so far.We here investigate the mechanisms involved in the long‐term persistence of the common grassland specialist, long‐lived, clonal plantAphyllanthes monspeliensisL. (Asparagaceae) after forest encroachment into semi‐natural Mediterranean calcareous grasslands in Catalonia (NEIberian Peninsula). For this purpose, we assess vegetative (above‐ground and below‐ground) and reproductive plant performance indicators and their habitat and landscape (current and historical) drivers.We confirm the existence of an extinction debt for this species, since current plant frequency is related to historical but not current connectivity, and we also find a positive effect of historical connectivity on seed set. In addition, current tree cover negatively affects individual size and above‐ground/below‐ground biomass ratio, and biotic soil acidification leads to a reduction in the flowering probability of individuals and stems.However, we also find that current connectivity negatively affects flowering and that tree cover enhances seed set. The forestation process, thus, also exerts a positive effect on some fitness traits, probably by providing a moister environment.Synthesis. Habitat loss and deterioration result in a decreased vegetative performance ofAphyllanthes monspeliensis, a grassland specialist, but show contrasting effects on its reproductive performance. This suggests that the species would perform better in open forests than grasslands in a context of climate change. However, further forest encroachment would increase light competition and soil acidification, threatening its persistence and promoting the payment of the extinction debt if no conservation measures are taken, like opening gaps in forests and enhancing grassland connectivity.

Grassland connectivity explains entomophilous plant species assemblages in an agricultural landscape of the Pampa Region, Argentina

AbstractThe Pampa grassland of Argentina is one of the most highly threatened biomes in the world. A high proportion of the original grassland cover has been transformed into land for agriculture or degraded. In the southern part of the region, fragmented semi‐natural grasslands over exposed rock still persist and connectivity between them is assumed to be crucial for maintaining viable populations. We quantified overall connectivity of grassland patches in a sector of the Southern Pampa region, and investigated the degree to which landscape connectivity explains entomophilous plant species assemblages in a subset of patches. We characterized each of the 301 patches in the landscape by their degree of intra‐patch and inter‐patch connectivity based on graph theory, and considering threshold dispersal distances from 100 to 1000 m. We surveyed entomophilous plant species in 39 grassland patches and classified the species in three categories (annual herbs, perennial herbs and shrubs) considering their different growth form and longevity. The influence of connectivity variables on entomophilous plant species assemblages variation was explored using Canonical Correspondence Analysis. Although grassland patches were poorly connected at all threshold distances, some of them were found to be critical for global connectivity. Connectivity significantly explained total, annual‐biennial and shrub assemblages for all threshold dispersal distances (6–13% of total variation). Variation in annual species assemblages was associated with intra‐patch and inter‐patch connectivity at short distance (100 m), while variation in shrub species assemblages was explained by intra‐patch and inter‐patch connectivity for distances between 100 m and 1000 m. This study evidenced the low connectivity of the study system, allowed the identification of critical areas for conservation, and provided valuable information to develop management strategies in increasingly human‐dominated landscapes.

Conservation Reserve Program mitigates grassland loss in the lesser prairie-chicken range of Kansas

Since the beginning of the 20th century, the overall occupied range of the lesser prairie-chicken (Tympanuchus pallidicinctus) has declined by 84% commensurate with population trends. Much of this decline has been attributed to the loss and fragmentation of native grasslands throughout the lesser prairie-chicken range. However, quantification of changes in land cover in the distribution of the lesser prairie-chicken is lacking. Our objectives were to (1) document changes in the areal extent and connectivity of grasslands in the identified lesser prairie-chicken range in Kansas, USA, (>60% of extant lesser prairie-chicken population) from the 1950s to 2013 using remotely sensed data and (2) assess the potential of the Conservation Reserve Program (U.S. Department of Agriculture Program converting cropland to permanent cover; CRP) to mitigate grassland loss. Digital land cover maps were generated on a decadal time step through spectral classification of LANDSAT images and visual analysis of aerial photographs (1950s and 1960s). Landscape composition and configuration were assessed using FRAGSTATS to compute a variety of landscape metrics measuring changes in the amount of grassland present as well as changes in the size and configuration of grassland patches. With the exception of a single regional portion of the range, nearly all of the grassland converted to cropland in the lesser prairie-chicken range of Kansas occurred prior to the 1950s. Prior to the implementation of CRP, the amount of grassland decreased 3.6% between the 1950s and 1985 from 18,455 km2 to 17,788 km2. Since 1985, the overall amount of grassland in the lesser prairie-chicken range has increased 11.9% to 19,898 km2 due to implementation of CRP, although the area of grassland decreased between 1994 and 2013 as CRP contracts were not renewed by landowners. Since 1986 grassland in Kansas became more connected and less fragmented in response to the CRP. While the CRP has been successful in increasing grassland quantity and connectivity throughout the lesser prairie-chicken range in Kansas, offsetting loss of grassland since the 1950s, abundance and occupied range of lesser prairie-chickens has declined since the 1980s, suggesting that habitat quality is the principal factor influencing population demography of the species. Although the CRP is contributing to conservation actions for lesser prairie-chickens, efforts to improve habitat quality throughout the range of the lesser prairie-chicken are likely necessary to meet management goals. Continuation of the CRP faces an uncertain future in the face of rising commodity prices, energy development, and reduction in program scope, leaving open the possibility that these areas that have created habitat for lesser prairie-chickens could be lost.

A graph-based approach to defend agro-ecological systems against water vole outbreaks

The cyclic spread of montane water vole populations in the grasslands of the Jura plateaus causes severe economic, ecological, and public-health problems. Since this phenomenon cannot be managed by massive use of the anticoagulant rodenticide bromadiolone, the challenge is to limit it by reducing regional-level connectivity through landscaping and agro-environmental interventions such as planting hedgerows, ploughing, and cultivating cereals. We used landscape graphs – a spatial modelling approach based on graph theory – to represent the grassland network and identify key areas for intervention. Several strategies were compared in terms of their capacity to fulfil operational requirements by interchanging patches and meta-patches as nodes of the graph, and least-cost distances and resistance distances to weight links. The combination of meta-patches and resistance distances provides a relevant basis on which to design concrete action to decrease regional-level connectivity of grasslands. The results also indicate that the usual removal method applied to the links of the graph would benefit from data on the statistical distribution of cost values along the shortest paths. More broadly, this suggests the modelling approach should be better matched the actual field interventions if the connectivity analysis is to be operational.

Assessing coexisting plant extinction debt and colonization credit in a grassland-forest change gradient.

Changes in species richness along the ecological succession gradient may be strongly determined by coexisting extinction debts of species from the original habitats and colonization credits of those from the replacing habitats. The magnitude of these processes and their causes remain largely unknown. We explored the extinction debt and colonization credit for grassland and forest specialist plants, respectively, and the local and landscape factors associated to the richness of these species groups in a 50-year process of forest encroachment into semi-natural Mediterranean grasslands. A set of sampling plots of persistent grasslands and forests and their transitional habitat (wooded grasslands) was selected within fixed-area sites distributed across the landscape. Our results confirm the extinction debt and suggest colonization credit (according to observed trends and model predictions) in wooded grasslands when compared to persistent forests, despite wooded grasslands and persistent forests having similar tree cover. Grassland connectivity and solar radiation had opposing effects on the richness of both grassland and forest specialists, and it is possible that the availability of seed sources from old forests may have accelerate the payment of colonization credit in the wooded grasslands. These results suggest that extinction debt and colonization credit have driven species turnover during the 50 years of forest encroachment, but at different rates, and that local and landscape factors have opposing effects on these two phenomena. They also highlight the importance of documenting biodiversity time lags following habitat change when they are still in progress in order to timely and adequately manage habitats of high conservation value such as the grasslands studied here.

Genetic assessment of environmental features that influence deer dispersal: implications for prion‐infected populations

AbstractThe landscape can influence host dispersal and density, which in turn, affect infectious disease transmission, spread, and persistence. Understanding how the landscape influences wildlife dispersal and pathogen epidemiology can enhance the efficacy of disease management in natural populations. We applied landscape genetics to examine relationships among landscape variables, dispersal of white‐tailed deer hosts and transmission/spread of chronic wasting disease (CWD), a fatal prion encephalopathy. Our focus was on quantifying movements and population structure of host deer in infected areas as a means of predicting the spread of this pathology and promoting its adaptive management. We analyzed microsatellite genotypes of CWD‐infected and uninfected deer from two disease foci (Southern Wisconsin, Northern Illinois). We quantified gene flow and population structure using FST, assignment tests, and spatial autocorrelation analyses. Gene flow estimates were then contrasted against a suite of landscape variables that potentially mediate deer dispersal. Forest fragmentation and grassland connectivity promoted deer movements while rivers, agricultural fields and large urbanized areas impeded movement. Landscape variables, deer dispersal, and disease transmission covaried significantly and positively in our analyses. Habitats with elevated host gene flow supported the concept of dispersal‐mediated CWD transmission by reflecting a concomitant, rapid CWD expansion. Large, interrelated social groups isolated by movement barriers overlapped disease foci, suggesting that philopatry exacerbated CWD transmission. Our results promote adaptive management of CWD by predicting patterns of its spread and identifying habitats at risk for invasion. Further, our landscape genetics approach underscores the significance of topography and host behavior in wildlife disease transmission.

Importance of Native Grassland Habitat for Den-Site Selection of Indian Foxes in a Fragmented Landscape

Fragmentation of native habitats is now a ubiquitous phenomenon affecting wildlife at various scales. We examined selection of den-sites (n = 26) by Indian foxes (Vulpes bengalensis) in a highly modified short-grassland landscape in central India (Jan-May, 2010). At the scale of the home-range, defined by an 800 m circular buffer around den sites, we examined the effect of land-cover edges and roads on selection of sites for denning using a distance-based approach. At the smaller den-area scale, defined by a 25 m x 25 m plot around den and paired available sites, the effect of microhabitat characteristics was examined using discrete-choice models. Indian foxes selected den-sites closer to native grasslands (t = -9.57, P < 0.001) and roads (t = -2.04, P = 0.05) than random at the home-range scale. At the smaller scale, abundance of rodents and higher visibility increased the odds of selection of a site by eight and four times respectively, indicating resource availability and predator avoidance to be important considerations for foxes. Indian foxes largely chose to den in human-made structures, indicated by the proportion of dens found in earthen bunds (0.69) and boulder piles (0.27) in the study area. With agricultural expansion and human modification threatening native short-grassland habitats, their conservation and effective management in human-dominated landscapes will benefit the Indian fox. The presence of some human-made structures within native grasslands would also be beneficial for this den-dependent species. We suggest future studies examine the impact of fragmentation and connectivity of grasslands on survival and reproductive success of the Indian fox.