Effects of grazing management on biodiversity across trophic levels–The importance of livestock species and stocking density in salt marshes

European coastal salt marshes are important for the conservation of numerous species of specialist plants, invertebrates, breeding and migratory birds. When these marshes are managed for nature conservation purposes, livestock grazing is often used to counter the dominance of the tall grass Elytrigia atherica, and the subsequent decline in plant species richness. However, it remains unclear what is the optimal choice of livestock species and stocking density to benefit biodiversity of various trophic levels. To fill this knowledge gap, we set up a triplicate, full factorial grazing experiment with cattle and horse grazing at low and high stocking densities (0.5 or 1 animal ha−1) at the mainland coast of the Dutch Wadden Sea. Here, we present the results after 4 years and integrate these with previously published results from the same experiment to assess effects of livestock grazing on various trophic groups. Stocking density affected almost all measured variables: high stocking densities favoured plant species richness and suppression of E. atherica, whereas low stocking densities favoured abundances of voles, pollinators and flowers. Densities of different functional groups of birds showed no significant response to the regimes, but tended to be somewhat higher under 0.5 horse and 1 cattle ha−1. Choice of livestock species had fewer and smaller effects than stocking density. Horse grazing was detrimental to vole density, and showed an interactive effect with stocking density for Asteraceae flower abundance. Multidiversity, a synthetic whole-ecosystem biodiversity measure, did not differ among regimes. These results are discussed in the light of other results from the same experiment. Because of these contrasting effects on different trophic groups, we advise concurrent application of different grazing regimes within a spatial mosaic, with the inclusion of long-term abandonment. High density horse grazing, however, is detrimental to biodiversity

Habitat amount and distribution modify community dynamics under climate change

Habitat fragmentation may present a major impediment to species range shifts caused by climate change, but how it affects local community dynamics in a changing climate has so far not been adequately investigated empirically. Using long-term monitoring data of butterfly assemblages, we tested the effects of the amount and distribution of semi-natural habitat (SNH), moderated by species traits, on climate-driven species turnover. We found that spatially dispersed SNH favoured the colonisation of warm-adapted and mobile species. In contrast, extinction risk of cold-adapted species increased in dispersed (as opposed to aggregated) habitats and when the amount of SNH was low. Strengthening habitat networks by maintaining or creating stepping-stone patches could thus allow warm-adapted species to expand their range, while increasing the area of natural habitat and its spatial cohesion may be important to aid the local persistence of species threatened by a warming climate

Spatially and Financially Explicit Population Viability Analysis of Maculinea alcon in The Netherlands

Background The conservation of species structured in metapopulations involves an important dilemma of resource allocation: should investments be directed at restoring/enlarging habitat patches or increasing connectivity. This is still an open question for Maculinea species despite they are among the best studied and emblematic butterfly species, because none of the population dynamics models developed so far included dispersal. Methodology/Principal Findings We developed the first spatially and financially explicit Population Viability Analysis model for Maculinea alcon, using field data from The Netherlands. Implemented using the RAMAS/GIS platform, the model incorporated both local (contest density dependence, environmental and demographic stochasticities), and regional population dynamics (dispersal rates between habitat patches). We selected four habitat patch networks, contrasting in several basic features (number of habitat patches, their quality, connectivity, and occupancy rate) to test how these features are affecting the ability to enhance population viability of four basic management options, designed to incur the same costs: habitat enlargement, habitat quality improvement, creation of new stepping stone habitat patches, and reintroduction of captive-reared butterflies. The PVA model was validated by the close match between its predictions and independent field observations on the patch occupancy pattern. The four patch networks differed in their sensitivity to model parameters, as well as in the ranking of management options. Overall, the best cost-effective option was enlargement of existing habitat patches, followed by either habitat quality improvement or creation of stepping stones depending on the network features. Reintroduction was predicted to generally be inefficient, except in one specific patch network. Conclusions/Significance Our results underline the importance of spatial and regional aspects (dispersal and connectivity) in determining the impact of conservation actions, even for a species previously considered as sedentary. They also illustrate that failure to account for the cost of management scenarios can lead to very different conclusions

Beyond climate envelopes: effects of weather on regional population trends in butterflies

Although the effects of climate change on biodiversity are increasingly evident by the shifts in species ranges across taxonomical groups, the underlying mechanisms affecting individual species are still poorly understood. The power of climate envelopes to predict future ranges has been seriously questioned in recent studies. Amongst others, an improved understanding of the effects of current weather on population trends is required. We analysed the relation between butterfly abundance and the weather experienced during the life cycle for successive years using data collected within the framework of the Dutch Butterfly Monitoring Scheme for 40 species over a 15-year period and corresponding climate data. Both average and extreme temperature and precipitation events were identified, and multiple regression was applied to explain annual changes in population indices. Significant weather effects were obtained for 39 species, with the most frequent effects associated with temperature. However, positive density-dependence suggested climatic independent trends in at least 12 species. Validation of the short-term predictions revealed a good potential for climate-based predictions of population trends in 20 species. Nevertheless, data from the warm and dry year of 2003 indicate that negative effects of climatic extremes are generally underestimated for habitat specialists in drought-susceptible habitats, whereas generalists remain unaffected. Further climatic warming is expected to influence the trends of 13 species, leading to an improvement for nine species, but a continued decline in the majority of species. Expectations from climate envelope models overestimate the positive effects of climate change in northwestern Europe. Our results underline the challenge to include population trends in predicting range shifts in response to climate change

Risks and opportunities of trophic rewilding for arthropod communities

Trophic rewilding is a restoration strategy focusing on the restoration of trophic interactions to promote self-regulating, biodiverse ecosystems. It has been proposed as an alternative to traditional conservation management in abandoned or defaunated areas. Arthropods constitute the most species-rich group of eukaryotic organisms, but are rarely considered in rewilding. Here, we first present an overview of direct and indirect pathways by which large herbivores and predators affect arthropod communities. We then review the published evidence of the impacts of rewilding with large herbivores on arthropods, including grey literature. We find that systematic monitoring is rare and that a comparison with a relevant control treatment is usually lacking. Nevertheless, the available data suggest that when the important process of top-down control of large-herbivore populations is missing, arthropod diversity tends to decrease. To ensure that rewilding is supportive of biodiversity conservation, we propose that if natural processes can only partially be restored, substitutes for missing processes are applied. We also propose that boundaries of acceptable outcomes of rewilding actions should be defined a priori, particularly concerning biodiversity conservation, and that action is taken when these boundaries are transgressed. To evaluate the success of rewilding for biodiversity, monitoring of arthropod communities should be a key instrument.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.</p

Utilization of heterogeneous grasslands by domestic herbivores: Theory to management

International audienc

The influence of wild boar (Sus scrofa) on microhabitat quality for the endangered butterfly Pyrgus malvae in the Netherlands

The decline of open habitats in Europe, such as semi-natural grasslands and heathlands, has caused a general decline in biodiversity, which has been well documented for butterflies. Current conservation practices often involve grazing by domestic livestock to maintain suitable butterfly habitats. The extent to which wild ungulates may play a similar role remains largely unknown. Through their rooting activity, wild boar could be effective to reduce grass encroachment and restore pioneer microhabitats that are vital to many grassland insects in temperate climates. Here, we assessed the microhabitat requirements of Pyrgus malvae, an endangered butterfly of heathland and grassland habitats in the Netherlands, with special attention for the influence of wild boar rooting. To date, oviposition site selection of this species has concentrated on calcareous grasslands, whereas we also include heathlands. Overall, larval occupancy was higher in warm, open and sparsely vegetated microhabitats, which supports earlier findings. In heathland, microhabitat occupancy was positively affected by bryophyte and litter cover. In heath-grassland mosaic, microhabitat occupancy was also influenced by bryophyte and litter cover, but in addition low grass cover increased occupancy by favouring host plants. In grassland, only low grass cover and host plant cover determined microhabitat quality. Across all habitats, occupied microhabitats were characterized by lower vegetation as well as higher average daytime temperatures than unoccupied microhabitats. We discovered that wild boar play an important role in reducing grass cover by shallow rooting in grass patches, thereby increasing host plant availability. Hence, wild boar may have an added value in maintaining and restoring P. malvae microhabitats in grassland habitats in addition to grazing by domestic livestock.ISSN:1366-638XISSN:1572-975