Patch occupancy in the endangered butterfly Lycaena helle in a fragmented landscape: effects of habitat quality, patch size and isolation

While there is agreement that both habitat quality and habitat network characteristics (such as patch size and isolation) contribute to the occupancy of patches by any given species, the relative importance of these factors is under debate. This issue is of fundamental ecological importance, and moreover of special concern for conservation biologists aiming at preserving endangered species. Against this background we investigated patch occupancy in the violet copper Lycaena helle, one of the rarest butterfly species in Central Europe, in the Westerwald area (Rhineland-Palatinate, Western Germany). Occupied (n = 102) differed from vacant (n = 128) patches in altitude, size, connectivity, availability of wind shelter, in the abundance of the larval host-plant, in the abundance of a grass species indicating favorable habitat conditions and in the abundance of nitrophilous plants. Overall, patch occupancy was primarily determined by patch size, connectivity and the abundance of the larval host plant, while all other parameters of habitat quality were of subordinate importance. Therefore, our findings suggest that even for extremely sedentary species such as L. helle habitat networks are decisive and—next to the preservation of habitat quality—need to be an integral part of any conservation management for this species.     

Persistence of species in a fragmented urban landscape: the importance of dispersal ability and habitat availability for grassland butterflies

Some species cope with, and survive in, urban areas better than others.From a conservation viewpoint it is important to understand why some species arerare or are excluded in the urban landscape, in order that we might take actionto conserve and restore species. Two ecological factors that might explain thedistribution and abundance of butterfly species in the urban landscape aredispersal ability and the availability of suitable habitat. The influence ofthese factors was assessed by examining the distribution and genetic structureof four grassland butterfly species in the West Midlands conurbation, UK. Thefour species differ in their distribution and abundance, mobility and habitatspecificity. No significant fit to the isolation-by-distance model was found forany of the study species at this spatial scale. MeanF _ST values revealed a non-significant level ofpopulation structuring for two species, Pieris napi (L.)and Maniola jurtina (L.), but moderate and significantpopulation differentiation for Pyronia tithonus (L.) andCoenonympha pamphilus (L.). Results suggest that thesespecies are limited more by the availability of suitable habitat than by theirability to move among habitat patches. Conservation strategies for thesegrassland species should initially focus on the creation and appropriatemanagement of suitable habitat. More sedentary species that have already beenexcluded from the conurbation may require a more complex strategy for theirsuccessful restoration.     

Viability of meta-populations of wetland birds in a fragmented landscape: testing the key-patch approach

The key patch approach assumes that metapopulations in fragmented landscapes are likely to be viable with at least one “key” sub-population that is sufficiently large to ensure re-colonization of surrounding minor habitat patches. It is based on a minimum viable number of breeding pairs and within-breeding season dispersal distance, linked to size of the animal and longevity. It was tested using census data of 15 wetland bird species (bearded tit, bluethroat, great reed warbler, sedge warbler, Savi’s warbler, grasshopper warbler, spotted crake, water rail, common snipe, common teal, garganey, little bittern, night heron, great bittern and marsh harrier) in 14 wetland complexes of variable size (3–55 km²) spread across the Netherlands (distances ranging 4–156 km). First, for each species it was assessed whether a wetland harbored a key subpopulation, which was the case for the sedge warbler (7 key subpopulations), grass-hopper warbler (2), water rail (2), bearded tit, bluethroat, Savi’s warbler, common teal, garganey, great bittern and marsh harrier (all one key subpopulation).Together with the adjacent sub-populations present within breeding season dispersal distance, 10 out of the 15 studied species formed viable meta-populations. This was compared with the trend in the census data of 13 species for 1990–2000 and was found to correspond significantly (likelihood ratio test, P = 0.003): species without a viable meta-population had declined (2 out of 4) or remained stable (2 out of 4), whereas viable meta-populations had increased (6 out of 9) or remained comparatively stable (2 out of 9). One wetland complex, the Oostvaardersplassen, stood out in that it haboured key sub-populations for 9 out of the 15 species studied. Variation in quantity of specific habitat (area or perimeter marshland, woodland or open water) in a wetland complex was of limited importance explaining abundance patterns, since all covaried strongly with total area among the wetland complexes, with the exception of water perimeter. Apparently, these wetlands on peat harbour largely similar landscapes. Indeed, population sizes of most birds covaried strongly and in a PCA two distinct clusters of species were identified that shared high numbers of breeding pairs in the same, larger, wetland complexes, the first (3 species) including the great reed warbler, and the second (9 species) the water rail.     

Importance of boreal grasslands in Sweden for butterfly diversity and effects of local and landscape habitat factors

A widespread decline in biodiversity in agro-ecosystems has been reported for several groups of organisms in Western Europe. The butterfly fauna was studied in 60 selected semi-natural grasslands in a coniferous-dominated boreal landscape in south-eastern Sweden. The aim was to investigate how butterfly assemblages were affected by the amount of semi-natural grasslands in the surrounding landscape. Furthermore, we wanted to determine if semi-natural grasslands in boreal landscapes harboured species otherwise declining in other parts of Europe. For each study site, the amounts of semi-natural grasslands in the landscape within radii of 500, 2,000 and 5,000 m were studied. Nine local habitat factors were also recorded. Only the amount of semi-natural grasslands within a 5,000 m radius could explain a significant part of the variation in butterfly composition, but there was no clear relationship between the amount of semi-natural grassland and butterfly diversity. Instead, this study showed that local habitat quality was very important for butterfly diversity at individual sites. Flower abundance, sward height and herb composition were the most important local factors. Patches surrounded by a small amount of semi-natural grasslands had high butterfly diversity, contrary to expectations. This may be explained by the fact that forest habitat provides a matrix with several features suitable for butterflies. The butterfly fauna was rich in species representative of low-productivity grasslands, species that are declining in other countries in Western Europe.     

The Large Blue butterfly, Phengaris [Maculinea] arion, as a conservation umbrella on a landscape scale: The case of the Czech Carpathians

Conservation umbrellas are charismatic species, the conservation of which also conserves the high diversity of associated plants and animals. The Large Blue butterfly, Phengaris [Maculinea] arion (Lepidoptera, Lycaenidae), is a textbook example of a charismatic endangered invertebrate, intensively studied throughout Europe and protected by the EU Habitat Directive. While surveying P. arion at the westernmost outskirts of the Carpathians (Javorniky and Vsetinske Mts.), within a stronghold of the species in the Czech Republic, we asked whether occupied sites differed from unoccupied ones in the composition of vascular plants and butterfly assemblages. The occupied sites (n = 65) were small pastures, including abandoned ones, with S to W exposure, located on rugged terrain and displaying a high microtopographic heterogeneity; the unoccupied sites (n = 101) were typically mown or intensively grazed. The vegetation of occupied sites was characteristic for non-intensive submountain pasture, butterfly assemblages were species richer, contained more specialised species, and significantly higher proportion of red-listed species. P. arion thus may act as an umbrella for a high number of species associated with traditional land use in the study area and elsewhere. Its survival will depend on the continuation of small-scale land use varying in space and time, and can be threatened by uniformisation of management, even if practised under the guise of agri-environmental payments.     

Foraging in a landscape mosaic: selection for energy and minerals in free-ranging cattle

Several studies have indicated the potential importance of nutrients, other than energy, in determining foraging decisions. A model was developed to test this idea, on the assumption of an intake maximization for different nutrients (energy, sodium and phosphorus). The model predictions were tested using field data from cattle grazing in a landscape mosaic of Pleistocene cover-sand and riverine grassland. Observations on foraging behaviour, food intake and diet composition were collected in thirteen 4-day-periods over 2 years. Habitat selection was determined by comparing the proportion of grazing time in different vegetation units with the available area proportion of the units. Two levels of habitat selection were examined: a micro-level (fine-scale, where vegetation units were considered separately) and a macro-level (coarse-scale, where vegetation units were combined to give selection at the landscape level). At the micro-level of habitat selection, no selection was apparent between the vegetation units of the riverine landscape, but the Deschampsia flexuosa unit was significantly selected for in the cover-sand landscape. At the landscape (macro-) level, the animals preferred the riverine landscape. The model revealed poor predictions of habitat occupancy on a micro-level. A much better prediction was obtained when vegetation units were combined at a macro-level. The D. flexuosa unit provided a higher energy intake, whereas the intake of sodium was higher in riverine grassland. Phosphorus proved relatively significant in determining habitat occupancy. Based on energy maximization alone, the model was a very poor predictor of habitat occupancy. It is argued that selection occurred mainly at the macro-level. The incorporation of different nutrient constraints in foraging models can then prove fruitful when seeking explanations of habitat occupancy. At the micro-level, difficulties for the animal in assessing nutrient availability may result in a less selective foraging pattern. However, the costs of increased selectivity may be greater than the benefits.     

Invasive birds in a novel landscape: habitat associations and effects on established species

Studying the relationships among introduced species, their preferred habitats, and native species can be important for predicting the effects of invasions on native populations. Examining the colonization of North America by the Eurasian collared‐dove Streptopelia decaocto, we quantified the habitat characteristics of sites most likely to be occupied by this invasive bird species in the early stages of the invasion. Further, we studied the relationship between collared‐dove abundance and the abundance of other dove species in the study area, anticipating a negative effect on established species following the introduction of a potential competitor. Linking satellite‐derived landcover data with winter bird community data gathered from 444 study sites in Florida, USA from 1999 to 2008, we found that collared‐doves were more likely to occur in landscapes that had been highly‐modified by human activity than in forested landscapes. Collared‐dove abundance increased as the proportion of the landscape characterized as low‐intensity development and medium/high‐intensity development increased. The probability of collared‐doves occurring at a site was also related to the spatial proximity of other sites reporting doves (positive spatial autocorrelation). Contrary to our expectations, the site‐level abundance of four other dove species all increased with collared‐dove abundance throughout the sampling period. Interactions between collared‐doves and native species should be further studied in different environments as this invasive bird rapidly colonizes North America.     

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.     

Diversity of management practices required to ensure conservation of rare and locally threatened plant species in grasslands: a case study at a regional scale (Lorraine, France)

The Lorraine region, in northeast France, harbours 77 protected plantspecies whose main localities are in grasslands. About 80% of them are very rareor rare (less than 15 localities) in that territory and are threatened by changes inagriculture. These species occur in a large range of grassland habitats,reflecting variability of climatic, hydrological and edaphic parameters, butalso of agricultural practices. A more precise analysis of managementrequirements was carried out for seven of these species, Euphorbiapalustris, Aster amellus, Pulsatillaalba, Carex hordeistichos, Thalictrumminus ssp. majus, Botrychiummatricariifolium and Ophioglossum vulgatum, whichwere represented on a triangle whose corners correspond to grazing, cutting andno or very low exploitation. It confirmed the large diversity of managementpractices required to ensure conservation of rare and threatened grassland plantspecies, even at a local level. These appropriate conservation measures havetherefore to be carried out or, at least, monitored by specialized natureconservation organizations.     

Site and landscape features ruling the habitat use and occupancy of the polecat (Mustela putorius) in a low density area: a multiscale approach

We studied the habitat of the polecat at different scales in a low density area. For this purpose we gathered data on the presence of the species and characterised them by location, home range and landscape scales. Polecats selected areas of high diversity close to, but not in, streams whilst avoiding intensively managed conifer plantations and dense urban areas. Variables determining the presence/absence of the species were found at home range scales, which implies that management and conservation practices for the species should be aimed mainly at this scale. Finally, our results agree with previously published works, which validate GIS-based approaches as a tool for carnivore management in areas with scarce data or in cases of rare species.     

The effects of fire frequency and grazing on tallgrass prairie productivity and plant composition are mediated through bud bank demography

Periodic fire, grazing, and a variable climate are considered the most important drivers of tallgrass prairie ecosystems, having large impacts on the component species and on ecosystem structure and function. We used long-term experiments at Konza Prairie Biological Station to explore the underlying demographic mechanisms responsible for tallgrass prairie responses to two key ecological drivers: fire and grazing. Our data indicate that belowground bud banks (populations of meristems associated with rhizomes or other perennating organs) mediate tallgrass prairie plant response. Fire and grazing altered rates of belowground bud natality, tiller emergence from the bud bank, and both short-term (fire cycle) and long-term (>15 year) changes in bud bank density. Annual burning increased grass bud banks by 25% and decreased forb bud banks by 125% compared to burning every 4 years. Grazing increased the rate of emergence from the grass bud bank resulting in increased grass stem densities while decreasing grass bud banks compared to ungrazed prairie. By contrast, grazing increased both bud and stem density of forbs in annually burned prairie but grazing had no effect on forb bud or stem density in the 4-year burn frequency treatment. Lastly, the size of the reserve grass bud bank is an excellent predictor of long-term ANPP in tallgrass prairie and also of short-term interannual variation in ANPP associated with fire cycles, supporting our hypothesis that ANPP is strongly regulated by belowground demographic processes. Meristem limitation due to management practices such as different fire frequencies or grazing regimes may constrain tallgrass prairie responses to interannual changes in resource availability. An important consequence is that grasslands with a large bud bank may be the most responsive to future climatic change or other global change phenomena such as nutrient enrichment, and may be most resistant to exotic species invasions.     

Habitat use by Oncifelis guigna and Pseudalopex culpaeus in a fragmented forest landscape in central Chile

Native forests in Chile have been replaced by exotic plantations, generating a mosaic of forest fragments immersed in a matrix of plantations and farms. This landscape change could affect habitat availability for native carnivores such as Oncifelis guigna (Felidae) and Pseudalopex culpaeus (Canidae). We determine the potential impact of native forest fragmentation on these species, assessinghabitat use by these carnivores. The study was carried out in continuous forest (150 ha), native forest fragments (<10 ha) and surrounding pine plantations in central Chile (35°59 S, 72°41 W). We placed scent-stations (SSs) in three types of habitat from January to August 2000, setting a total of 620 SSs to determine habitat selection. We characterized structure and composition of 100 m² of vegetation aroundevery SS, and measured its distance to nearest native forest patch, road and bottom creek. O. guigna preferred habitats with dense bush cover, far from roads and close to large patches of native forest, being almost exclusively restricted to this type of habitat. On the other hand, P. culpaeus preferred openhabitats, close to roads, relying extensively on pine plantations but scarcely using forest and forest fragments. Our results suggest that native forest fragmentation, considering habitat use only, would have a negative effect on O. guigna populations. Thus, forest size reduction and isolation may reduce O.guigna survival in a pine dominated landscape. In contrast, P. culpaeus, a generalist species that would use habitat depending on its abundance, may adapt to changes in this landscape.     

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.     

Assessing the impact of local habitat variables and landscape context on riparian birds in agricultural,urbanized, and native landscapes

Large tracts of natural habitat are being replaced by agriculture and urban sprawl in Mediterranean regions worldwide. We have limited knowledge about the effects of human activities on native species in these landscapes and which, if any, management practices might enhance the conservation of native biodiversity within them. Through a citizen volunteer bird-monitoring project, we compared bird abundance and species richness in northern Californian riparian zones surrounded by vineyards, urban areas, and natural areas. We assessed both local and landscape-level variables that may enhance native bird diversity in each land use type. We also demonstrate a new statistical approach, generalized estimating equations, to analyze highly variable data, such as that collected by volunteers. Avian abundance was highly correlated with both landscape context and local habitat variables, while avian richness was correlated with local habitat variables, specifically shrub richness, and percent of tree cover. In particular, shrub species richness has a strong positive correlation with riparian-preferring bird species. This suggests that active local management of riparian zones in human-dominated landscapes can increase our ability to retain native bird species in these areas.     

Dry grassland plant diversity conservation using low-intensity sheep and goat grazing management: case study in Prague (Czech Republic)

After abandonment, dry grassland (Festuco-Brometea) areas decline due to gradual overgrowing by woody species and the expansion of perennial tall grass species. Dry grassland vegetation was formed by extensive livestock grazing, thus grazing is considered one of the most natural methods for managing this type of vegetation. Six years after introducing low-intensity sheep and goat grazing in seven nature reserves in Prague (Czech Republic), the following impact of this management on dry grassland vegetation was observed: The cover of expansive woody species, particularly Ligustrum vulgare, and to a smaller extent Cornus sanguinea and Prunus spinosa declined. In addition, a significant, long-term declining trend of the expansive species Arrhenatherum elatius was also observed. Also the cover of Pimpinella saxifraga and Allium senescens declined significantly with regard to statistical evaluation. On the contrary, the cover of Achillea millefolium, Centaurea stoebe, Securigera varia, Elytrigia repens, Erysimum crepidifolium, Falcaria vulgaris, Fallopia convolvulus and Verbascum lychnitis increased. The cover of species characteristic of dry grasslands (Festuco-Brometea) increased significantly. No changes were observed in the number and cover of the Red List species. In addition, the presence of nitrophilous and ruderal species increased. Species diversity also significantly increased. From our findings we can conclude that managing dry grasslands with low-intensity grazing can help to keep dry grassland vegetation in good condition and conserve its plant diversity. Nomenclature: Kubát et al. (2002) for taxa and Moravec et al. (1995) for syntaxa.     

The changing status of the Chalkhill Blue butterfly <Emphasis Type="Italic">Polyommatus coridon</Emphasis> in the UK: the impacts of conservation policies and environmental factors

The Chalkhill Blue Polyommatus coridon is a widespread butterfly of lowland calcareous grassland in southern Britain and is considered a good indicator of habitat condition. Polyommatus coridon has been identified as a Species of Conservation Concern in the UK Biodiversity Action Plan due to a greater than 25% decline in range size since the 1950s, with losses due to the combined effects of habitat destruction, agricultural intensification and neglect. Analysis of annual butterfly monitoring data (transects) collected at 161 sites from 1981 to 2000 show a three-fold population recovery had occurred. The increases were at established sites, with no re-colonisations or range expansion detected. The 1980s population increase coincided with increases across the species range in stock and rabbit Oryctolagus cuniculus grazing, as well as greater protection and management of sites through protected areas and nature reserves. During the 1990s agri-environment schemes were thought to be the main conservation and policy mechanism driving the favourable conservation status of P. coridon, by facilitating appropriate habitat restoration and management. Weather played a part in the species recovery, with warm, but wet summers associated with increases in abundance. The research provides strong evidence of an important conservation success with the UK Biodiversity Action Plan, with implications for other specialist biodiversity.     

The effects of sheep grazing on seedling establishment and survival in grassland

This paper examines the effects of sheep and insect grazing on the generation of natural gaps in turf and the establishment of seedlings therein. The site is on an old field on limestone. There were five sheep grazing treatments: ungrazed, and grazed briefly in spring, briefly in autumn, in autumn or in summer and autumn. The first three of these treatments also contained plots in which insecticide was applied regularly during the growing season. Pins of increasing size (1.6 mm–12.8 mm diameter) were lowered at grid intersections in permanent quadrats to record gap type and the occurrence of seedlings on seven dates over 15 months.Heavily-grazed plots had more bare ground in spring and more herb seedlings established in them. Seedlings of annual species of Bromus were able to establish in gaps (bare ground and litter) of smaller size than was required by herb seedlings (which had much smaller seeds). The use of an insecticide increased seedling establishment in October in ungrazed and in spring-grazed paddocks but decreased it in autumn-grazed paddocks. This may indicate the greater importance of insect herbivory in making gaps in the matted sward of autumn-grazed plots.Seedlings which established in October 1986 and March 1987 were more likely to die than those establishing earlier in 1986. This may be because of winter-kill and especially vigorous spring vegetation growth respectively. Seedling mortality was not affected by gap size or grazing treatment (unless such effects operated before we detected the seedlings).     

Predator identity and consumer behavior: differential effects of fish and crayfish on the habitat use of a freshwater snail

Predators can alter the outcome of ecological interactions among other members of the food web through their effects on prey behavior. While it is well known that animals often alter their behavior with the imposition of predation risk, we know less about how other features of predators may affect prey behavior. For example, relatively few studies have addressed the effects of predator identity on prey behavior, but such knowledge is crucial to understanding food web interactions. This study contrasts the behavioral responses of the freshwater snail Physellagyrina to fish and crayfish predators. Snails were placed in experimental mesocosms containing caged fish and crayfish, so the only communication between experimental snails and their predators was via non-visual cues. The caged fish and crayfish were fed an equal number of snails, thereby simulating equal prey mortality rates. In the presence of fish, the experimental snails moved under cover, which confers safety from fish predators. However, in the presence of crayfish, snails avoided benthic cover and moved to the water surface. Thus, two species of predators, exerting the same level of mortality on prey, induced very different behavioral responses. We predict that these contrasting behavioral responses to predation risk have important consequences for the interactions between snails and their periphyton resources. Received: 1 June 1998 / Accepted: 12 October 1998     

The impact of forest spread on a marginal population of a protected peony (<Emphasis Type="Italic">Paeonia officinalis</Emphasis> L.): the importance of conserving the habitat mosaic

In the Mediterranean region of Europe, land-use changes have allowed for rapid colonisation of open habitats by woody species. As a result, it is critical to gather information on how protected species in open habitats respond to forest spread in such areas. Our objective is to quantify whether spatial heterogeneity of the vegetation associated with recent forest closure influences demographic structure and maternal fertility in a population of the protected Paeonia officinalis L. In closed woodland, adult plants of P. officinalis are almost exclusively vegetative, in open habitats seedlings are rare and on the woodland edge there is a relative over-representation of flowering plants and seedlings. Forest closure dramatically reduces flowering frequency, but has no significant effect on maternal fertility of flowering plants. The spatial aggregation of seedlings close to the maternal plants suggests that dispersal is spatially restricted. Together, these results suggest that the viability of the population requires a transitional habitat between open garrigues or grassland with spaced trees and woodland. A management programme incorporating tree and shrub thinning and cutting of parcels in rotation to maximise the length of the forest edge could maintain a habitat mosaic that favours the persistence of this species in the study site.