Fragmented Calcareous Grasslands Research Articles

A plant-pollinator metanetwork along a habitat fragmentation gradient.

To understand how plant-pollinator interactions respond to habitat fragmentation, we need novel approaches that can capture properties that emerge at broad scales, where multiple communities engage in metanetworks. Here we studied plant-pollinator interactions over 2years on 29calcareous grassland fragments selected along independent gradients of habitat size and surrounding landscape diversity of cover types. We associated network centrality of plant-pollinator interactions and grassland fragments with their ecological and landscape traits, respectively. Interactions involving habitat specialist plants and large-bodied pollinators were the most central, implying that species with these traits form the metanetwork core. Large fragments embedded in landscapes with high land cover diversity exhibited the highest centrality; however, small fragments harboured many unique interactions not found on larger fragments. Intensively managed landscapes have reached a point in which all remaining fragments matter, meaning that losing any further areas may vanish unique interactions with unknown consequences for ecosystem functioning.

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

In Central Europe, agricultural intensification has led to increasing fragmentation and loss of semi-natural habitats. In turn, ecosystem services such as pollination are being lost when insect pollinators depend on semi-natural habitats. Calcareous grasslands are a highly threatened, biodiverse type of semi-natural habitat that may substantially support wild pollinators and pollination services to surrounding habitats. Here, we studied spillover of pollinators and pollination services from calcareous grassland fragments of different sizes into the surrounding landscape for solitary and social bees, as well as hoverflies. We selected eight grassland fragments of varying sizes (0.05–9.41 ha) surrounded by simplified agricultural landscapes near Göttingen, Germany. To quantify pollination spillover, we established Phacelia tanacetifolia (Boraginaceae) plots at distances ranging from 0 to 400 m from grassland edges alongside field roads. Our experiment revealed the importance of calcareous grassland fragments as sources of solitary bees, of which visitation to Phacelia plants decreased with increasing distance from fragments. Larger grassland fragments supported more than twice as many solitary bees as smaller ones. The limited foraging range of solitary bees appeared to be compensated by other groups, such as bumblebees and hoverflies, which were less affected by distance, suggesting a greater forage radius and/or independence from the grassland fragments as habitat. Seed production of Phacelia plants increased with overall pollinator visitation and solitary bee visits specifically, but did not decrease with distance. In conclusion, calcareous grasslands need to be conserved or restored as major bee habitats, which support spillover of pollination services into the adjacent agricultural landscape.

Increasing connectivity enhances habitat specialists but simplifies plant\u2013insect food webs

Strong declines of grassland species diversity in small and isolated grassland patches have been observed at local and landscape scales. Here, we study how plant–herbivore interaction webs and habitat specialisation of leafhopper communities change with the size of calcareous grassland fragments and landscape connectivity. We surveyed leafhoppers and plants on 14 small (0.1–0.6 ha) and 14 large (1.2–8.8 ha) semi-natural calcareous grassland fragments in Central Germany, differing in isolation from other calcareous grasslands and in the percentage of arable land in the surrounding landscape (from simple to complex landscapes). We quantified weighted trophic links between plants and their phytophagous leafhoppers for each grassland fragment. We found that large and well-connected grassland fragments harboured a high portion of specialist leafhopper species, which in turn yielded low interaction diversity and simple plant-leafhopper food webs. In contrast, small and well-connected fragments exhibited high levels of generalism, leading to higher interaction diversity. In conclusion, food web complexity appeared to be a poor indicator for the management of insect diversity, as it is driven by specialist species, which require high connectivity of large fragments in complex landscapes. We conclude that habitat specialists should be prioritized since generalist species associated with small fragments are also widespread in the surrounding landscape matrix.

Insect and plant traits drive local and landscape effects on herbivory in grassland fragments

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

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.

Partitioning wild bee and hoverfly contributions to plant-pollinator network structure in fragmented habitats.

The risk of ecosystem function degradation with biodiversity loss has emerged as a major scientific concern in recent years. Possible relationships between taxonomic diversity and magnitude and stability of ecosystem processes build upon species' functional characteristics, which determine both susceptibility to environmental change and contribution to ecosystem properties. The functional diversity within communities thus provides a potential buffer against environmental disturbance, especially for properties emerging from interactions among species. In complex plant-pollinator networks, distantly related taxa spanning a great trait diversity shape network architecture. Here, we address the question of whether network properties are maintained after habitat loss by complementary contributions of phylogenetically distant pollinator taxa. We quantified contributions of wild bees and hoverflies to network structure (connectance, network specialization, specialization asymmetry) in 32 calcareous grassland fragments varying in size. Although hoverflies are often regarded less susceptible to environmental change than wild bees, species richness of both taxa was similarly affected by habitat loss. The associated loss of 80% of interactions resulted in small and tightly connected networks, which was more strongly attributed to wild bee loss than hoverfly loss. Networks in small fragments were less specialized due to equivalent losses of species and interactions in both pollinators and plants. Because wild bee and hoverfly loss contributed similarly to declining network specialization, we conclude that trait diversity among distantly related pollinators does not necessarily provide insurance against functional homogenization during community disassembly following habitat loss.

Past and potential future effects of habitat fragmentation on structure and stability of plant-pollinator and host-parasitoid networks.

Habitat fragmentation is a primary threat to biodiversity, but how it affects the structure and stability of ecological networks is poorly understood. Here, we studied plant-pollinator and host-parasitoid networks on 32 calcareous grassland fragments covering a size gradient of several orders of magnitude and with amounts of additional habitat availability in the surrounding landscape that varied independent of fragment size. We find that additive and interactive effects of habitat fragmentation at local (fragment size) and landscape scales (1,750 m radius) directly shape species communities by altering the number of interacting species and, indirectly, their body size composition. These, in turn, affect plant-pollinator, but not host-parasitoid, network structure: the nestedness and modularity of plant-pollinator networks increase with pollinator body size. Moreover, pollinator richness increases modularity. In contrast, the modularity of host-parasitoid networks decreases with host richness, whereas neither parasitoid richness nor body size affects network structure. Simulating species coextinctions also reveals that the structure-stability relationship depends on species' sensitivity to coextinctions and their capacity for adaptive partner switches, which differ between mutualistic and antagonistic interaction partners. While plant-pollinator communities may cope with future habitat fragmentation by responding to species loss with opportunistic partner switches, past effects of fragmentation on the current structure of host-parasitoid networks may strongly affect their robustness to coextinctions under future habitat fragmentation.

An ecological connectivity network maintains genetic diversity of a flagship wildflower, Pulsatilla vulgaris

Ecological connectivity networks have been proposed as an efficient way to reconnect communities in fragmented landscapes. Yet few studies have evaluated if they are successful at enhancing actual functional connectivity (i.e. realized dispersal or gene flow) of focal species, or if this enhanced connectivity is enough to maintain genetic diversity and fitness of plant populations. Here we test the efficacy of an ecological connectivity network implemented in southern Germany since 1989 to reconnect calcareous grassland fragments through rotational shepherding. We genotyped 1449 individuals from 57 populations and measured fitness-related traits in 10 populations of Pulsatilla vulgaris, a flagship species of calcareous grasslands in Europe. We tested if the shepherding network explained functional connectivity in P. vulgaris and if higher connectivity translated to higher genetic diversity and fitness of populations. We found that population-specific Fst was lowest in populations that had high connectivity within the shepherding network, and that well-connected populations within the network had significantly higher genetic diversity than ungrazed and more isolated grazed populations. Moreover, genetic diversity was significantly positively correlated with both seed set and seed mass. Together our results suggest that the implementation of an ecological shepherding network is an effective management measure to maintain functional connectivity and genetic diversity at the landscape scale for a calcareous grassland specialist. Populations with reduced genetic diversity would likely benefit from inclusion, or better integration into the ecological connectivity network. Our study demonstrates the often postulated but rarely tested sequence of positive associations between connectivity, genetic diversity, and fitness at the landscape scale, and provides a framework for testing the efficacy of ecological connectivity networks for focal species using molecular genetic tools.

Functional connectivity as an indicator for patch occupancy in grassland specialists

Habitat specialists living in metapopulations are sensitive to habitat fragmentation. In most studies, the effects of fragmentation on such species are analyzed based on Euclidean inter-patch distances. This approach, however, ignores the role of the landscape matrix. Recently, therefore, functional distances that account for the composition of the landscape surrounding the habitat patches have been used more frequently as indicators for patch occupancy. However, the performance of functional and non-functional connectivity measures in predicting patch occupancy of such species has never been compared in a multi-species approach.Here we evaluate the effect of habitat connectivity on the patch occupancy of 13 habitat specialists from three different insect orders (Auchenorrhyncha, Lepidoptera, Orthoptera) in fragmented calcareous grasslands. In order to calculate functional distances we used four different sets of resistance values and rankings. We then modelled species’ occurrence using both Euclidean and functional (based on least-cost modelling) inter-patch distances as predictors.We found that functional connectivity measures provided better results than the non-functional approach. However, a functional connectivity measure that was based on very coarse land-cover data performed even better than connectivity measures that were based on much more detailed land-use data.In order to take into account possible effects of the landscape matrix on patch occupancy by habitat specialists, future metapopulation studies should use functional rather than Euclidean distances whenever possible. For practical applications, we recommend a ‘simple approach’ which requires only coarse land-cover data and in our study performed better than all other functional connectivity measures, even more complex ones.

Effect of Rotational Shepherding on Demographic and Genetic Connectivity of Calcareous Grassland Plants

Response to habitat fragmentation may not be generalized among species, in particular for plant communities with a variety of dispersal traits. Calcareous grasslands are one of the most species-rich habitats in Central Europe, but abandonment of traditional management has caused a dramatic decline of calcareous grassland species. In the Southern Franconian Alb in Germany, reintroduction of rotational shepherding in previously abandoned grasslands has restored species diversity, and it has been suggested that sheep support seed dispersal among grasslands. We tested the effect of rotational shepherding on demographic and genetic connectivity of calcareous grassland specialist plants and whether the response of plant populations to shepherding was limited to species dispersed by animals (zoochory). Specifically, we tested competing dispersal models and source and focal patch properties to explain landscape connectivity with patch-occupancy data of 31 species. We fitted the same connectivity models to patch occupancy and nuclear microsatellite data for the herb Dianthus carthusianorum (Carthusian pink). For 27 species, patch connectivity was explained by dispersal by rotational shepherding regardless of adaptations to zoochory, whereas population size (16% species) and patch area (0% species) of source patches were not important predictors of patch occupancy in most species. [Correction made after online publication, February 25, 2014: Population size and patch area percentages were mistakenly inverted, and have now been fixed.] Microsite diversity of focal patches significantly increased the model variance explained by patch occupancy in 90% of the species. For D. carthusianorum, patch connectivity through rotational shepherding explained both patch occupancy and population genetic diversity. Our results suggest shepherding provides dispersal for multiple plant species regardless of their dispersal adaptations and thus offers a useful approach to restore plant diversity in fragmented calcareous grasslands.

Linking life history traits to pollinator loss in fragmented calcareous grasslands

AbstractTo gain insight into the drivers of pollinator loss, a holistic approach to land-use change including habitat size, isolation, habitat quality and the surrounding landscape matrix is necessary. Moreover, species’ responses to land-use change may differ depending on their life history traits such as dispersal ability, trophic level, or sociality. We assessed species richness and life history traits of wild bees in 32 calcareous grasslands in central Germany that differ in size, connectivity, resource availability and landscape context. Declining habitat area and, to a lesser degree, reduced diversity of the surrounding landscape were the key factors negatively influencing species richness. In the community-wide analysis, small body size and solitary reproduction were traits that made species particularly vulnerable to habitat loss. Contrary to our expectations, cleptoparasitic species were not more affected by reduced habitat area and landscape diversity than nest-building species. We performed further detailed trait analyses within the family Halictidae to prevent possible confounding effects due to trait correlations across families. Here, social as opposed to solitary species were more affected by habitat loss. We conclude that the opposite pattern observed for all social bees was mainly caused by large-sized social bumblebee species with high mobility and large foraging distances. Our results demonstrate the risks of concealed trait interference when analyzing community-wide patterns of life history traits. As a consequence, conservation requirements of small social bee species might be overlooked by generalizations from community responses.

Butterfly responses to environmental factors in fragmented calcareous grasslands

Although there is much research showing a strong negative effect of habitat fragmentation and deterioration on the viability of different insect populations and on species richness, the effect of fragmentation is modified by other local and landscape factors. One of the most substantial gaps in knowledge is whether species are similar in their response to the same environmental factors and if their response mirrors response of the entire community. From the conservation point of view this knowledge is of primary importance in planning conservation actions, yet these studies are rare. In this paper we test the relative effects of habitat patch and landscape characteristics on butterflies inhabiting calcareous grasslands in southern Poland. Butterfly species richness and abundance were positively affected by patch size and wind shelter. In the case of species richness there was also a positive effect of plant species richness. Butterfly diversity was enhanced in wind sheltered patches, and commonness (non-rarity) enhanced by distance to buildings and by shorter vegetation. Multivariate analysis suggested differences in the responses of individual species to the examined environmental variables, with some species more responsive to patch size and shelter and others to sward height. The conservation of butterfly communities requires sensible and complex management to ensure high habitat diversity. The most important challenge for future studies on calcareous grasslands is to formulate a model of management that guarantees high species richness and conservation of each individual species.

Testing coexistence of extinction debt and colonization credit in fragmented calcareous grasslands with complex historical dynamics

Calcareous grasslands are among the most species-rich ecosystems in temperate countries. However, these ecosystems have suffered from fragmentation and destruction during the last century. We studied the response of calcareous grassland plant diversity to landscape changes in Belgium. Results indicated that high area loss (since 1965) old habitat patches exhibited an extinction debt inverse to low area loss old habitat patches, little depending on the area loss threshold (60%, 70%, 80% or 90%) considered for the distinction between the high and low area loss patches. However, human activities also created new habitat patches in the landscape and therefore provided opportunities for calcareous grassland plant species to colonize new habitats. This also provided opportunities to study species colonization abilities in the context of habitat restoration. We analyzed species richness in new patches compared to old patches in order to detect colonization credit. We detected the presence of a colonization credit in new patches when using high loss old patches (area loss >80%, exhibiting an extinction debt) or all old patches as a reference. However, when the reference was low loss old patches alone (area loss <80%, less likely to exhibit an extinction debt), no colonization credit was detected. In addition, species composition was similar between new patches and old patches. These results are encouraging for restoration programs. However, the results indicated that the presence of an extinction debt in reference habitats could lead to inaccurate conclusions in restoration monitoring. Therefore, extinction debt should be considered when choosing reference habitats to evaluate restoration success.

Increasing patch area, proximity of human settlement and larval food plants positively affect the occurrence and local population size of the habitat specialist butterfly Polyommatus coridon (Lepidoptera: Lycaenidae) in fragmented calcareous grasslands

Which factors influence the occurrence, population size and density of species in fragmented habitat patches are key questions in population and conservation ecology. Metapopulation theory predicts that larger and less isolated habitat patches should positively influence species occurrence and population size. However, recent studies have shown that habitat quality, human activity and permeability of the landscape surrounding habitat patches may be also important. In this paper we test the relative effects of habitat patch characteristics, human settlement and landscape permeability on the occurrence, local population size and density of the Chalk-hill Blue Polyommatus coridon a charismatic butterfly inhabiting calcareous grasslands in a fragmented landscape in southern Poland. Patch occupancy rate (corrected for the butterfly detection probability) was 0.45. Habitat patch area, proximity of human settlement and cover of larval food plants positively affected occurrence of the Chalk-hill Blue. Local population size of the Chalk-hill Blue was positively affected by patch area and proximity of human settlement, and negatively by patch isolation. Local density was higher in patches located close to human settlement. Our study is one of the few showing a positive effect of human settlement on a grassland specialist butterfly although the mechanism hidden behind this phenomenon is unknown and requires further examination. In order to maintain local populations of the Chalk-hill Blue in southern Poland, conservation action should be focused on large, closely connected calcareous grasslands. Moreover, extensive management of this habitat should be maintained by local inhabitants who are better placed to undertake such work.

What determines the distribution of a flightless bush-cricket (Metrioptera brachyptera) in a fragmented landscape?

Based on metapopulation theory, isolation, patch size and habitat quality within patches have recently been identified as the most critical parameters determining the persistence of species. In the special case of flightless and sedentary Orthoptera species, taking into account the low dispersal ability, species survival probably depends more on habitat quality than on isolation. The aim of this study was to document how landscape (patch size, isolation and climate) and microhabitat (vegetation structure, microclimate and land use) factors influence patch occupancy and population densities, respectively, of a flightless bush-cricket (Metrioptera brachyptera) in fragmented calcareous grasslands. In summer 2005 patch occupancy of M. brachyptera was assessed in 68 calcareous grassland patches of the Diemel Valley (central Germany). Among these, 26 patches with 80 plots were selected to characterise M. brachyptera habitats in detail. On each plot, bush-cricket density was sampled in an area of 20 m2 using a 0.5 m2 box quadrat. At the landscape level (patches) in 46 (68%) of 68 studied calcareous grassland patches M. brachyptera was present. Patch occupancy increased with annual precipitation and patch size but was independent of altitude, annual temperature and isolation. At the microhabitat level (plots), population density of M. brachyptera decreased with land-use intensity and increased with vegetation height. In addition, a high litter accumulation was adverse for M. brachyptera. Given the low explanatory power of isolation for patch occupancy, conservation of flightless and sedentary insects, such as M. brachyptera, should primarily focus on improving habitat quality. For M. brachyptera and other stenotopic calcareous grassland species we therefore recommend traditional rough grazing with sheep, which creates a heterogenous habitat structure and avoids the accumulation of too much litter.

Human influence lowers plant genetic diversity in communities with extinction debt

Summary 1. Loss of plant species induced by adverse human influence and habitat fragmentation might be delayed due to a slow response to changed environmental conditions. This phenomenon is known as extinction debt, which can lead to the underestimation of actual threats to biodiversity. To adequately estimate the condition of recently fragmented plant communities and avoid future loss of species, good indicators of forthcoming extinctions are needed. 2. We studied the behaviour of genetic diversity of a relatively common habitat specialist grass Briza media in fragmented calcareous grasslands in which the extinction debt has been previously documented. Species richness in this system is shown to be determined by historical landscape patterns and human population densities prevailing centuries ago. We hypothesize that genetic diversity in this grassland system is related to current landscape patterns and contemporary human impact since genetic diversity might react more quickly to environmental changes than species diversity. 3. In contrast to species diversity, genetic diversity was indeed best described by current connectivity of grasslands. Additionally, genetic diversity was negatively related to current human population density, indicating an adverse effect of contemporary human settlements on studied species. The faster response of genetic diversity to changed environmental conditions compared to species richness was further supported by the absence of an expected correlation between species richness and genetic diversity. 4. Human population density a century ago had a positive effect on genetic diversity. A similar effect has been demonstrated for species richness in these grasslands, indicating that traditional land use in the past has supported the development of both genetic and species diversity. 5. Synthesis. Genetic diversity of Briza media in fragmented communities is reacting quickly to changes in landscape structure and anthropogenic pressure. Our results confirm that plant species can be prone to genetic deterioration due to habitat fragmentation and negative anthropogenic impact even if the decline in species richness has been delayed by extinction debt. Thus, a decrease of population genetic diversity in fragmented communities can be taken as the first indication of future species losses.

Patch Size and Landscape Effects on Pollinators and Seed Set of the Horseshoe Vetch, Hippocrepis comosa, in an Agricultural Landscape of Central Europe

Agricultural land use intensification has caused a considerable decline of once common semi-natural habitats leaving only small and isolated habitat remnants within a homogeneous landscape matrix. Populations of flowering plant species in these remaining habitat fragments are also declining and can not offer sufficient resources for potential pollinators. The loss of pollinators and consequential pollination limitation is especially severe for obligately out-crossing plant species. In this study, pollination and reproductive success of Hippocrepis comosa was examined. Hippocrepis comosa L is a self-incompatible, declining plant species occurring on fragmented remnants in semi-natural calcareous grassland habitats in an agricultural landscape in Southern Lower Saxony, Germany. Plant-pollinator interactions were analysed in small, medium, and large plant patches in 15 differently sized calcareous grassland fragments surrounded by landscape matrices of differing complexity. Flower visitors were observed during three 15-minute observations, pollen supplementation experiments were performed to test for pollination limitation, and fruits from the plant patches were collected to calculate seed set. Hippocrepis comosa showed evidence of pollination limitation because hand-pollinated flowers set more seeds per inflorescence than open-pollinated flowers and seed set was strongly reduced by decreased visitation rates. Pollinators were most abundant in large patches and in diverse landscapes. Visitation rate was not affected by patch size. Hence, in order to maintain plant-pollinator interactions in an agricultural landscape, conservation efforts should include the preservation of calcareous grasslands that can support sufficiently large patches of a plant species and offer ample rewards for pollinators and the establishment of a diverse agricultural landscape around the semi-natural habitats that will further enhance pollinator abundance.

Does seed retention potential affect the distribution of plant species in highly fragmented calcareous grasslands?

Long‐distance dispersal is a crucial factor in the life‐cycle of plants, especially in our modern, highly fragmented landscapes. Because natural herds of large animals have disappeared and grazing practices have been abandoned, important potential vectors for seed dispersal over large distances may have been lost. In the context of the re‐establishment of grazing management for nature conservation purposes, it is therefore important to gain insight in the ability of grazing animals to act as seed dispersal vectors. Whereas local dispersal mainly occurs through standard vectors typically described based on morphological adaptations of the diaspore, large herbivores act as non‐standard seed dispersers. Therefore, traditional dispersal classes are loosing scientific relevance and continuous predictors of dispersal potential have been proposed. Here, we explored whether dispersal related plant traits, including the “seed retention potential”, could explain the distribution patterns of 180 plant species over 64 fragmented semi‐natural calcareous grasslands in Belgium. The distribution of habitat specialist plant species was strongly determined by the degree of isolation of the grasslands. Interestingly, species distribution patterns were clearly linked with a species’ potential to migrate through large grazers, as quantified by its retention potential: species producing seeds with high retention capacity were less affected by habitat isolation. Categorical dispersal classes based on seed morphology did not explain a species’ response to fragment isolation. Although seed retention potential outperformed simple seed dimensional traits, plant height, which is an indicator of epizoochorous attachment potential, was even more important. Therefore we suggest further extension of the epizoochorous retention potential model by incorporating basic ecological mechanisms that effectively contribute to successful dispersal events.

Does seed retention potential affect the distribution of plant species in highly fragmented calcareous grasslands?

Does seed retention potential affect the distribution of plant species in highly fragmented calcareous grasslands?

The Chalk-hill Blue Polyommatus coridon (Lycaenidae, Lepidoptera) in a highly fragmented landscape: How sedentary is a sedentary butterfly?

The habitats of many species are fragmented. Therefore, the survival in a metapopulation depends on the stability of the single populations and the amount of movements between patches. We chose the calcareous grassland specialist butterfly species Polyommatus coridon as a model. As study area, we selected a mosaic-like landscape in Rhineland-Palatinate (western Germany) with several well preserved calcareous grassland fragments. We marked a total of 2,211 individuals during July and August 2003. The overall recapture ratio was 7.1%. The estimated mean butterfly densities over the whole flight season ranged from 52 to 487 individuals per hectare. The within-patch movements were relatively low (13.3%) compared with the between-patch movements (3.2%). Therefore, the metapopulation structure appears to be intact in our study area.