Nitrogen deposition impacts on biodiversity in terrestrial ecosystems : Mechanisms and perspectives for restoration
Wallis de Vries, Michiel ; Bobbink, Roland - \ 2017
Biological Conservation 212 (2017)pt. B. - ISSN 0006-3207
A nitrogen index to track changes in butterfly species assemblages under nitrogen deposition
Wallis de Vries, Michiel ; Swaay, Chris A.M. van - \ 2017
Biological Conservation 212 (2017)pt. B. - ISSN 0006-3207 - p. 448 - 453.
Biodiversity - Butterflies - Global change - Indicators - Insects - Nitrogen deposition
The impacts of nitrogen deposition (N) on animal communities are still poorly understood in comparison to plant communities. Long-term monitoring of community changes may contribute to this understanding, complementing experimental studies on underlying mechanisms. Butterflies are particularly suitable for such analyses, because the different species cover a broad gradient of productivity, their ecological traits are well-known, monitoring data are available in a growing number of countries, and the short life history of butterflies ensures a rapid response to changing environmental conditions.Here, we use species-specific nitrogen optima to develop a community nitrogen index (CNI) for butterflies in the Netherlands. Over a 25-year period (1990-2015), data from the Dutch Butterfly Monitoring Scheme reveal a significant increase in the CNI in response to high nitrogen deposition levels. However, the rate of increase is declining, in close parallel with reduced nitrogen deposition loads. The continuing increase indicates that nitrogen deposition still exceeds the critical nitrogen load of butterfly communities in the Netherlands. Overall, the relative increase of butterflies from more productive environments reflects the advantage, under high nitrogen availability, of mobile and multivoltine species with high reproductive capacity, rapid larval development and hibernation as pupae or adults. We discuss the perspectives and limitations in applying the CNI at both national and local scales. We propose that, when taking the critical nitrogen load of the examined butterfly community into account, the CNI may prove a valuable tool to track changes of biotic communities in relation to nitrogen deposition.
Differentiating the effects of climate and land use change on European biodiversity : A scenario analysis
Vermaat, Jan E. ; Hellmann, Fritz A. ; Teeffelen, Astrid J.A. van; Wallis de Vries, Michiel - \ 2017
Ambio 46 (2017)3. - ISSN 0044-7447 - p. 277 - 290.
Climate envelope modelling - Dry grasslands - Habitat connectivity - Land use change - Species sensitivity database - SRES scenario articulation - Wetlands - 016-3982 - 017-3997
Current observed as well as projected changes in biodiversity are the result of multiple interacting factors, with land use and climate change often marked as most important drivers. We aimed to disentangle the separate impacts of these two for sets of vascular plant, bird, butterfly and dragonfly species listed as characteristic for European dry grasslands and wetlands, two habitats of high and threatened biodiversity. We combined articulations of the four frequently used SRES climate scenarios and associated land use change projections for 2030, and assessed their impact on population trends in species (i.e. whether they would probably be declining, stable or increasing). We used the BIOSCORE database tool, which allows assessment of the effects of a range of environmental pressures including climate change as well as land use change. We updated the species lists included in this tool for our two habitat types. We projected species change for two spatial scales: the EU27 covering most of Europe, and the more restricted biogeographic region of ‘Continental Europe’. Other environmental pressures modelled for the four scenarios than land use and climate change generally did not explain a significant part of the variance in species richness change. Changes in characteristic bird and dragonfly species were least pronounced. Land use change was the most important driver for vascular plants in both habitats and spatial scales, leading to a decline in 50–100% of the species included, whereas climate change was more important for wetland dragonflies and birds (40–50 %). Patterns of species decline were similar in continental Europe and the EU27 for wetlands but differed for dry grasslands, where a substantially lower proportion of butterflies and birds declined in continental Europe, and 50 % of bird species increased, probably linked to a projected increase in semi-natural vegetation. In line with the literature using climate envelope models, we found little divergence among the four scenarios. Our findings suggest targeted policies depending on habitat and species group. These are, for dry grasslands, to reduce land use change or its effects and to enhance connectivity, and for wetlands to mitigate climate change effects.
Grazing and biodiversity: from selective foraging to wildlife habitats
Wallis de Vries, M.F. - \ 2016
In: Mountain pastures and livestock farming facing uncertainty: environmental, technical and socio-economic challenges / Casasús, I., Lombardi, G., Zaragoza : Centre International de Hautes Etudes Agronomiques Méditerranéennes (Options Méditerranéennes series A: Mediterranean Seminars 116) - ISBN 9782853525596 - p. 177 - 187.
Livestock grazing in low-intensity farming systems is a key aspect in the conservation of Europe's biodiversity, which reaches high levels of species richness in semi-natural grasslands. With the demise of traditional grazing systems, the design of viable low-intensity grazing systems for the future requires a good understanding of grazing impacts on biodiversity. Here, I review various scale-dependent aspects of selective grazing and how they may affect biodiversity. Insects such as butterflies are well-suited to elucidate small-scale impacts of grazing intensity. They highlight the importance of viewing grazing impacts in a framework of spatial heterogeneity and successional dynamics. In order to optimise these successional dynamics, grazing management may adopt techniques such as rotational grazing and strategic placement of mineral licks. However, we still lack a good evidence base on the effects of targeted grazing practices on biodiversity. The challenge to solve this gap can be met by a combination of creative field experiments that focus on the mechanisms of biodiversity responses and adaptive management that builds on a continuous feedback from sound monitoring.
|Politiek landschap moet vergroenen
Wallis de Vries, M.F. - \ 2016
De argusvlinder: hoe keren we de afname van een 'gewone vlindersoort'?
Stip, A. ; Wallis de Vries, M.F. - \ 2016
De Levende Natuur 117 (2016)2. - ISSN 0024-1520 - p. 46 - 51.
016-3723 - 016-3923
Er zijn momenteel in Nederland maar weinig vlindersoorten die zo hard
achteruitgaan als de Argusvlinder (Lasiommata megera). In goed twintig
jaar tijd verdween maar liefst 98% van de populatie in ons land. En dat terwijl
het tot voor kort een heel ‘gewone’ vlindersoort was in een breed scala aan
biotopen. Om het tij te keren heeft De Vlinderstichting recent een beschermingsplan voor de Argusvlinder opgesteld. Met de daaruit voortkomende
maatregelen en onderzoek is nieuwe kennis opgedaan over de ecologie van de Argusvlinder en de problemen waar de soort mee kampt. In dit artikel presenteren we deze kennis. Op basis daarvan geven we richtlijnen voor het beheer van het habitat van de Argusvlinder.
Beheeroptimalisatie Zuid-Limburgse hellingschraallanden : effecten van gefaseerde begrazing op bodem, vegetatie en fauna
Nijssen, Marijn ; Bobbink, Roland ; Geertsma, Marten ; Scherpenisse, Miriam ; Huiskes, Rik ; Kuper, Jan ; Smits, Nina ; Bohnen-Verbaarschot, Evi ; Verbeek, Peter ; Versluijs, Remco ; Wallis de Vries, Michiel ; Weijters, Maaike ; Wouters, Bart - \ 2016
Driebergen : VBNE, Vereniging van Bos- en Natuurterreineigenaren (Rapport / Vereniging van Bos- en Natuurterreineigenaren nr. OBN-209-HE) - 183
Effects of grazing management on biodiversity across trophic levels – The importance of livestock species and stocking density in salt marshes
Klink, Roel van; Nolte, Stefanie ; Mandema, Freek S. ; Lagendijk, D.D.G. ; Wallis de Vries, Michiel ; Bakker, Jan P. ; Esselink, Peter ; Smit, Christian - \ 2016
Agriculture, Ecosystems and Environment 235 (2016). - ISSN 0167-8809 - p. 329 - 339.
Birds - Butterflies - Cattle - Flower-visiting insects - Horses - Plants - Vegetation - Wetland
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.
Landscape complexity and farmland biodiversity: Evaluating the CAPtarget on natural elements
Cormont, A. ; Siepel, H. ; Clement, J. ; Melman, Th.C.P. ; Wallis de Vries, M.F. - \ 2016
Journal for Nature Conservation 30 (2016). - ISSN 1617-1381 - p. 19 - 26.
Increasing pressures on natural areas and limited conservation budgets require, particularly in rural landscapes in the Western world, an immediate answer to the question how much natural area is required to provide a sustainable future for wild plant and animal species on farmland. The European Union proposed in its Common Agricultural Policy that 3–7% of EU farmland should be managed as ecological focus area (EFA) in order to halt biodiversity loss. For the first time, we empirically assessed the implications of this policy by evaluating the effects of the density of natural elements in agricultural landscapes on multi-taxon species richness, including vascular plants, breeding birds, butterflies, hoverflies, dragonflies, and grasshoppers for an entire European country. We found that species richness increased either as linear or as a logarithmic function of the proportion of natural elements in the landscape, but not with a sigmoid function as predicted by the ‘intermediate landscape complexity’ hypothesis. Even landscapes with 3–7% of natural elements harboured generally 37–75% of maximum species richness, indicating good potential of implementing the CAP target to preserve farmland biodiversity. However, differences between the 3 and 7% limits were considerable for butterflies, birds, and hoverflies. Also, the shape of the species richness response was shown to differ between landscape types for butterflies. Thus, it may be necessary to develop tailor-made guidelines at regional levels.
How much Biodiversity is in Natura 2000? : the “Umbrella Effect” of the European Natura 2000 protected area network : technical report
Sluis, T. van der; Foppen, R. ; Gillings, Simon ; Groen, T.A. ; Henkens, R.J.H.G. ; Hennekens, S.M. ; Huskens, K. ; Noble, David ; Ottburg, F.G.W.A. ; Santini, L. ; Sierdsema, H. ; Kleunen, A. van; Schaminee, J.H.J. ; Swaay, C. van; Toxopeus, Bert ; Wallis de Vries, M.F. ; Jones-Walters, L.M. - \ 2016
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2738) - 147
biodiversity - habitats directive - birds directive - natura 2000 - statistical analysis - geographical information systems - biodiversiteit - habitatrichtlijn - vogelrichtlijn - natura 2000 - statistische analyse - geografische informatiesystemen
In order to assess the significance of the presumed “umbrella effect” of Natura 2000 areas the European Commission initiated a study, in 2013, to address the following questions: 1) Which are, amongst the species regularly occurring within the European territory of the EU-28 Member States, those that significantly benefit from the site conservation under the EU Birds and Habitats Directive? 2) What is the percentage of all species occurring in the wild in the EU that benefit significantly from Natura 2000? 3) How significant is the contribution of Natura 2000 in relation to the objective of halting and reversing biodiversity loss? The approach used existing data, and covered the terrestrial mammals, birds, reptiles, amphibian, butterfly and plant species. The analysis is mostly based on statistical distribution models and GIS processing of species distribution data in relation to their presence within protected areas of the Natura 2000 network. The main findings for all species groups were: Animal species for which Natura 2000 areas were not specifically designated occur more frequently inside Natura 2000 than outside (in particular breeding birds and butterflies). These species do, therefore, gain benefit from the protected areas network. The species for which Natura 2000 areas were designated generally occur more frequently within the Natura 2000 site boundaries than the nonannex species; this is in particular the case for birds and butterflies, for amphibians and reptiles the difference is negligible. More specific conclusions and findings, as well as discussion of these results and implications for further studies are included in the report.
Herstel kwaliteit van natte heide in het zandlandschap
Wallis de Vries, M.F. ; Bobbink, R. ; Jansen, A.J.M. ; Vogels, J.J. - \ 2016
Landschap : tijdschrift voor landschapsecologie en milieukunde 33 (2016)2. - ISSN 0169-6300 - p. 110 - 115.
016-3951 - natuurbeheer - ecologisch herstel - heidegebieden - bodemkwaliteit - flora - vegetatie - fauna - toegepast onderzoek - bodems van waterrijke gebieden - grondwater - nature management - ecological restoration - heathlands - soil quality - flora - vegetation - fauna - applied research - wetland soils - groundwater
Het verspreidingsgebied van natte heiden is in omvang min of meer gelijk gebleven sinds de laatste ontginningen. De kwaliteit blijft echter een dalende trend vertonen door de inwerking van stikstofdepositie en verdroging. Tegelijkertijd zijn er veelbelovende resultaten geboekt door nieuwe vormen van herstelbeheer. OBN heeft daarvoor de kennisbasis ontwikkeld. In dit artikel worden de daaruit voortvloeiende inzichten uiteen gezet en worden uitdagingen voor de toekomst geschetst.
Contrasting responses of insect communities to grazing intensity in lowland heathlands
Wallis de Vries, Michiel ; Noordijk, Jinze ; Colijn, Ed O. ; Smit, John T. ; Veling, Kars - \ 2016
Agriculture, Ecosystems and Environment 234 (2016). - ISSN 0167-8809 - p. 72 - 80.
Biodiversity - Butterflies - Grasshoppers - Grazing - Heathlands - Insects
Grazing at low stocking rates is often recommended for the preservation of the characteristic biodiversity of open landscapes. However, the fine-tuning of grazing management still lacks a good evidence base. This is particularly true for insect communities, as available evidence indicates that these are more vulnerable to grazing than plant communities. The outcome, however, may be expected to differ between insect species. Here, we analysed the impact of different grazing intensities on insect communities from lowland heathlands in the Netherlands. Firstly, we use detailed data on butterfly distribution and abundances to analyse population responses of 10 butterfly species to heathland grazing management. Secondly, we investigated species responses to grazing intensity on 16 field locations across a range of insect groups (butterflies, day-active moths, grasshoppers, and ants). We hypothesized that species from early successional stages would benefit from grazing whereas late-successional species would suffer from grazing. Moreover, we expected summer grazing to have less beneficial effects than year-round grazing. Both hypotheses were largely supported by our results. Species responses to grazing contrasted between early and late successional species. Variation in species responses were strongly linked to grazing intensity and soil moisture, reflecting species-specific niches in relation to vegetation structure and microclimate. We conclude that low-intensity year-round cattle grazing or herded sheep grazing may promote insect biodiversity in large, heterogeneous heathlands, whereas targeted or rotational grazing may be advisable in smaller areas.
Mogelijkheden voor herstelbeheer in hellingbossen op kalkrijke bodem in Zuid-Limburg : resultaten praktijkproeven: omvorming van voormalig middenbos naar gevarieerd opgaand bos
Hommel, P.W.F.M. ; Bijlsma, R.J. ; Eichhorn, K.A.O. ; Ouden, J. den; Waal, R.W. de; Wallis de Vries, M.F. ; Eichhorn, L. ; Goudzwaard, L. ; Heijerman, T. ; Kemmers, R.H. ; Prick, M.J.M. ; Smeets, Floris - \ 2016
Driebergen : Vereniging van Bos- en Natuurterreineigenaren - 155
Using a phenological network to assess weather influences on first appearance of butterflies in the Netherlands
Kolk, Henk Jan Van Der; Wallis de Vries, Michiel ; Vliet, Arnold J.H. Van - \ 2016
Ecological Indicators 69 (2016). - ISSN 1470-160X - p. 205 - 212.
Anthocharis cardamines - Butterflies - Climate change - Monitoring network - Phenology - Plant-host interaction
Phenological responses of butterflies to temperature have been demonstrated in several European countries by using data from standardized butterfly monitoring schemes. Recently, phenological networks have enabled volunteers to record phenological observations at project websites. In this study, the quality of the first appearance data of butterflies from the Dutch phenological network 'De Natuurkalender' was examined and these data were then used to analyze trends in butterfly appearance between 2001 and 2013, the effects of climatic factors on appearance of butterflies as well as the phenological interaction of one butterfly species, Anthocharis cardamines, and its two major host plants. Although phenological networks are relatively unstructured, this study shows that data from De Natuurkalender were highly comparable to more standardized data collected by the Dutch Butterfly Monitoring Scheme. No trend in first appearance of any butterfly species was found during the time period 2001-2013. The first appearance dates of most butterflies showed, however, a clear relationship with spring temperature. Higher temperatures, especially in March and April, advanced the first appearance of butterflies. Therefore, with climatic warming in the future, earlier appearance of butterflies is expected. Although climate warming is a potential threat for phenological mismatches between different trophic levels, this study shows a similar temperature response of A. cardamines and its main host plants in the Netherlands. However, as only few phenological interactions between species are examined, further research including rarer monophagous butterfly species and their host plants is needed.
|Effecten van omvorming van hellingbossen naar ongelijkvormig hooghout op de vlinderfauna
Wallis de Vries, M.F. ; Prick, M.J.M. - \ 2015
Natuurhistorisch Maandblad 104 (2015)12. - ISSN 0028-1107 - p. 243 - 247.
De Keizersmantel als indicator voor het herstel van lichte en viooltjesrijke hellingbossen
Omon, B. ; Veling, K. ; Wallis de Vries, M.F. - \ 2015
De Levende Natuur 116 (2015)5. - ISSN 0024-1520 - p. 204 - 207.
bosgebieden - bossen - soortenrijkdom - fauna - lepidoptera - nymphalidae - waardplanten - ecosystemen - habitats - zuid-limburg - bosbeheer - natuurbeheer - woodlands - forests - species richness - fauna - lepidoptera - nymphalidae - host plants - ecosystems - habitats - zuid-limburg - forest administration - nature management
Een deel van de soorten die eens kenmerkend waren voor de hellingbossen in Zuid-Limburg is afgenomen of zelfs verdwenen. Het dichtgroeien van de bossen na het beëindigen van hakhoutbeheer zou een verklaring kunnen zijn, maar is dat ook zo? In dit artikel worden de ecologische eisen van de fauna van hellingbossen besproken aan de hand van de Keizersmantel. Ingegaan wordt op de vraag in welke mate de ecologische randvoorwaarden voor de Keizersmantel worden bepaald door het aanbod van waardplanten en door het microklimaat.
Susceptibility of pollinators to ongoing landscape changes depends on landscape history
Aguirre-Gutiérrez, J. ; Biesmeijer, J.C. ; Loon, E. van; Reemer, M. ; Wallis de Vries, M.F. ; Carvalheiro, L.G. - \ 2015
Diversity and Distributions 21 (2015)10. - ISSN 1366-9516 - p. 1129 - 1140.
Aim Pollinators play an important role in ecosystem functioning, affecting also crop production. Their decline may hence lead to serious ecological and economic impacts, making it essential to understand the processes that drive pollinator shifts in space and time. Land-use changes are thought to be one of the most important drivers of pollinators’ loss, and there is increasing investment on pollinator-friendly landscape management. However, it is still unclear whether landscape history of a given region determines how pollinator communities respond to further landscape modification. Location The Netherlands. Methods Using geographically explicit historical landscape and pollinator data from the Netherlands, we evaluated how species richness changes of three important pollinator groups (bees, hoverflies and butterflies) are affected by landscape changes related to habitat composition, fragmentation and species spillover potential and whether such effects depend on the historical characteristics of the landscape. Results The effect of landscape changes varied between different pollinator groups. While bumblebee richness benefited from increases in edges between managed and natural systems, other bees benefited from increases in landscape heterogeneity and hoverfly richness was fairly resistant to land-use changes. We found that for the majority of the pollinators past landscape characteristics conditioned, the more recent pollinator richness changes. Landscapes that historically had more suitable habitat were more susceptible to display hoverfly declines (caused by drivers not considered in this study). Landscapes that historically had greater spillover potential were more likely to suffer butterfly richness declines and the bumblebee assemblages were more susceptible to the effects of fragmentation. Main conclusions The diversity of responses of the pollinator groups suggest that multispecies approaches that take group-specific responses to land-use change into account are highly valuable. These findings emphasize the limited value of a one-size-fits-all biodiversity conservation measure and highlight the importance of considering landscape history when planning biodiversity conservation actions.
Impact of nitrogen deposition on larval habitats: the case of the Wall Brown butterfly Lasiommata megera
Klop, E. ; Omon, B. ; Wallis de Vries, M.F. - \ 2015
Journal of Insect Conservation 19 (2015)2. - ISSN 1366-638X - p. 393 - 402.
british butterflies - herbivorous insects - pararge-aegeria - limitation - climate - biodiversity - adaptation - phosphorus - landscape - trends
Nitrogen deposition is considered as one of the main threats to biodiversity and ecosystem functioning. Three mechanisms have been proposed to explain the detrimental effect of excess nitrogen on butterflies: loss of host plants, deterioration of food plant quality and microclimatic cooling in spring. Here, we investigated whether these mechanisms might explain the dramatic recent decline of the Wall Brown butterfly Lasiommata megera. Monitoring data from the Netherlands indeed show a greater decline at higher critical load exceedance of nitrogen deposition. Loss of host plants is not a likely explanation of the decline for this grass-feeding species. In a greenhouse experiment, we only found beneficial effects of nitrogen fertilization on larval performance, which seems to rule out a nutritional cause; application of a drought treatment did not result in significant effects. Microclimatic conditions at overwintering larval sites of L. megera and the related but increasing Pararge aegeria provided a possible clue. In comparison with larval sites of P. aegeria, those of L. megera showed higher temperatures at the mesoscale and less plant cover and more dead plant material at the microscale. L. megera caterpillars were also found closer to the shelter of vertical structures. The greater dependence on warm microclimates suggests that microclimatic cooling through excess nitrogen contributes to the recent decline of L. megera.
Defoliation and soil compaction jointly drive large-herbivore grazing effects on plants and soil arthropods on clay soil
Klink, R. van; Schrama, M. ; Nolte, S. ; Bakker, J.P. ; Wallis de Vries, M.F. ; Berg, M.P. - \ 2015
Ecosystems 18 (2015)4. - ISSN 1432-9840 - p. 671 - 685.
salt-marsh - nitrogen mineralization - wadden sea - mountain pastures - grassland - collembola - management - diversity - growth - cow
In addition to the well-studied impacts of defecation and defoliation, large herbivores also affect plant and arthropod communities through trampling, and the associated soil compaction. Soil compaction can be expected to be particularly important on wet, fine-textured soils. Therefore, we established a full factorial experiment of defoliation (monthly mowing) and soil compaction (using a rammer, annually) on a clay-rich salt marsh at the Dutch coast, aiming to disentangle the importance of these two factors. Additionally, we compared the effects on soil physical properties, plants, and arthropods to those at a nearby cattle-grazed marsh under dry and under waterlogged conditions. Soil physical conditions of the compacted plots were similar to the conditions at cattle-grazed plots, showing decreased soil aeration and increased waterlogging. Soil salinity was doubled by defoliation and quadrupled by combined defoliation and compaction. Cover of the dominant tall grass Elytrigia atherica was decreased by 80% in the defoliated plots, but cover of halophytes only increased under combined defoliation and compaction. Effects on soil micro-arthropods were most severe under waterlogging, showing a fourfold decrease in abundance and a smaller mean body size under compaction. Although the combined treatment of defoliation and trampling indeed proved most similar to the grazed marsh, large discrepancies remained for both plant and soil fauna communities, presumably because of colonization time lags. We conclude that soil compaction and defoliation differently affect plant and arthropod communities in grazed ecosystems, and that the magnitude of their effects depends on herbivore density, productivity, and soil physical properties.
Effects of large herbivores on grassland arthropod diversity
Klink, R. van; Plas, F. van der; Noordwijk, C.G.E. ; Wallis de Vries, M.F. ; Olff, H. - \ 2015
Biological Reviews 90 (2015)2. - ISSN 1464-7931 - p. 347 - 366.
ungrazed chalk grassland - ground beetle coleoptera - plant-species richness - grazing management - phytophagous insects - seminatural grasslands - community structure - tallgrass prairie - long-term - butterfly communities
Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity.