Landscape context of habitat fragmentation and the diversity of plants, arthropods and snails on calcareous grasslands

Landnutzungsänderungen, Habitatverlust und Fragmentierung gehören zu den Hauptursachen des weltweiten Biodiversitätsrückgangs. In Mitteleuropa zählen Kalkmagerrasen zu den artenreichsten Lebensräumen. Sie weisen eine hohe Vielfalt an xero- und thermophilen Pflanzen- und Invertebratenarten auf, sind jedoch zunehmend durch landwirtschaftliche Intensivierung und Nutzungsaufgabe gefährdet. Sie sind auf Beweidung und Mahd angewiesen, was jedoch für die Landwirte heutzutage unwirtschaftlich geworden ist. Daher finden sich zunehmend kleine Fragmente innerhalb einer für die meisten der spezialisierten Magerrasenarten ungeeigneten, von intensiver Landwirtschaft geprägten Umgebung. Der erste Teil dieser Arbeit untersucht den Einfluss der Fragmentgröße, der Habitatkonnektivität, der Zusammensetzung der umgebenden Landschaft und der Pflanzenartenzahl auf die Zusammensetzung der Zikadengemeinschaft. Zikaden sind eine überaus artenreiche Gruppe phytophager Insekten mit enger Bindung an die Vegetationsstruktur und -zusammensetzung. In der Umgebung von Göttingen wählten wir 14 große (>1 ha) und 14 kleine (<1 ha) Kalkmagerrasenflächen entlang von Gradienten zunehmender Konnektivität mit anderen Magerrasenflächen, zunehmender Pflanzenartenzahl und zunehmender Landschaftskomplexität, d.h. dem Prozentsatz Ackerfläche innerhalb eines 500 m-Radius, aus. Zunehmende Isolation verringerte die Zikadenartenzahl in einfachen (von Feldern geprägten), jedoch nicht in komplexen Landschaften. Dieser Effekt wurde von den Generalisten getrieben. Die Artenzahl der Generalisten nahm auf kleinen Fragmenten mit zunehmender Konnektivität zu, wogegen sie auf großen Flächen unverändert blieb. Weiterhin nahm die Artenzahl der Generalisten mit steigender Pflanzenartenzahl auf vernetzten Magerrasen stärker zu als auf unvernetzten. Unsere Ergebnisse zeigen, dass die Insektenartenvielfalt auf Kalkmagerrasenfragmenten nicht nur durch Konnektivität allein geprägt wird, sondern vielmehr von einem Zusammenspiel aus Konnektivität, Landschaftszusammensetzung und Pflanzenartenzahl bestimmt wird. Im zweiten Teil dieser Arbeit verfolgen wir das Ziel, zur Lösung der sogenannten SLOSS-Debatte (“Single Large Or Several Small”) beizutragen, in der diskutiert wird, ob es besser ist, wenige große oder mehrere kleine Fragmente eines Habitattyps zu erhalten. Man nimmt an, dass kleine Fragmente aufgrund der größeren abgedeckten geographischen Distanzen eine größere Heterogenität und dadurch eine höhere Gesamtartenzahl aufweisen. Dagegen weisen große Fragmente stabilere Lebensraumbedingungen und größere Populationen auf. Neben Zikaden und Pflanzen wurden auch Daten zu Wanzen und 114 Schnecken aufgenommen. Sowohl die Gesamtartenzahl aller vier Taxa als auch die Zahl der Spezialisten war auf mehreren kleinen Fragmenten wesentlich höher als auf einem oder zwei großen Fragmenten gleicher Gesamtgröße. Jedoch war die Artenzusammensetzung auf großen und kleinen Fragmenten unterschiedlich und einige der seltensten Spezialisten waren an große Flächen gebunden. Hingegen spielte die Zusammensetzung der umgebenden Landschaft keine wichtige Rolle für Artenzahl und -zusammensetzung. Diese Ergebnisse stellen den Fokus auf entweder große oder kleine Habitatfragmente infrage. Für einen erfolgreichen Biodiversitätserhalt ist daher der Schutz sowohl großer als auch kleiner Habitatfragmente zwingend notwendig. Im dritten Teil dieser Arbeit untersuchen wir den Einfluss der Bewirtschaftungsart (Beweidung, Mahd, Nutzungsaufgabe), der Landschaftszusammensetzung und Konnektivität auf die Artenzahl, Artenzusammensetzung und merkmalsbasierte Reaktionen (Körpergröße und Rote Liste-Status) von neun Taxa: Pflanzen, Schmetterlinge, Bienen, Heuschrecken, Schwebfliegen, Spinnen, Wanzen, Kurzflügler und Zikaden. Wir wählten 30 kleine Kalkmagerrasenfragmente (<1 ha) entlang von unabhängigen Konnektivitäts- und Landschaftskomplexitätsgradienten aus. Ein zunehmender Prozentsatz an Ackerfläche in der Umgebung der Fragmente führte zu einem Verlust von 29 % der Gesamtartenzahl. Wir nehmen an, dass Landschaften, die von Ackerfläche dominiert werden, weniger Alternativhabitat und Nahrungsressourcen bieten, was zu einer verringerten Artenzahl führt. Habitatkonnektivität erhöhte im Allgemeinen die Artenzahl. Dieser Effekt war bei den großen, vermutlich ausbreitungsfähigeren Arten eines Taxons stärker ausgeprägt als bei den kleinen Arten. Beweidung hatte einen deutlich negativeren Einfluss auf die Artenzahl als Mahd (einmal jährlich) oder kurzzeitige Nutzungsaufgabe (5-15 Jahre). Der Grund dafür könnte der durch Beweidung verursachte größere Schaden und die Entnahme der Nahrungsressourcen phytophager Insekten sein. Zudem führte jeder der drei Bewirtschaftungsweisen zu einer unterschiedlichen Artenzusammensetzung aller Taxa. Daher sollte die bevorzugte Bewirtschaftungsoption kleiner Kalkmagerrasenfragmente ein Wechsel zwischen Mahd und kurzzeitiger Nutzungsaufgabe in Kombination mit einer Diversifizierung der umgebenden Landschaft sein. Zusammenfassend lässt sich sagen, dass die allgemein verbreitete Konzentration auf große Habitatfragmente überdacht werden sollte, da der Schutz sowohl kleiner als auch großer Fragmente unerlässlich ist. Bei der Planung von Schutzmaßnahmen für fragmentierte Offenlandlebensräume sind lokale Einflüsse wie Fragmentgröße und Bewirtschaftung zwar wichtig, aber nicht ausreichend: Landschaftsfaktoren wie Habitatkonnektivität und Landschaftszusammensetzung müssen ebenfalls in die Schutzbemühungen mit einbezogen werden um das langfristige Überleben von spezialisierten Pflanzen- und Invertebratenarten zu sichern.Land-use change, habitat loss and fragmentation are among the main drivers of the decline of biodiversity worldwide. In Central Europe, calcareous grasslands belong to the most species-rich habitats. They harbour a great diversity of xero- and thermophilic plant and invertebrate species but are increasingly under threat from agricultural intensification and abandonment. They depend on grazing or mowing, but today, these traditional land use practices have become unprofitable for farmers. Therefore, increasingly smaller fragments are embedded within a matrix that is often unsuitable for most of the plant and invertebrate species specialised on calcareous grasslands. The first part of this thesis analyses the effects of fragment size, connectivity, the composition of the surrounding landscape and plant species richness on leafhopper community structure. Leafhoppers are a highly diverse group of phytophagous insects with a close connection to vegetation structure and composition. We selected 14 large (>1 ha) and 14 small (<1 ha) fragments of calcareous grassland in the surroundings of Göttingen along gradients of increasing connectivity to other calcareous grasslands, increasing plant species richness and in the increasing complexity of the surrounding landscape, i.e. the percentage of arable land within a 500 m radius. Increasing habitat isolation reduced leafhopper species richness in simple (dominated by arable crops), but not in complex landscapes. This effect was driven by generalist species. Moreover, generalist species richness increased with increasing connectivity on small fragments, whereas it remained stable on large fragments. Finally, generalist species richness increased more steeply with increasing plant species richness on connected than on isolated fragments, suggesting that more colonisers reach connected fragments and can subsequently use the available plant resources. Our results show that insect biodiversity on fragmented calcareous grasslands not only depends on habitat connectivity but that it is interactively affected by habitat connectivity, landscape composition, habitat area and plant species richness. Isolated fragments that are either small or located in simple landscapes are less likely to receive immigrants after extinction events, potentially leading to a gradual reduction in species richness over time. In the second part of this thesis we aim to contribute to the resolution of the so-called SLOSS debate (“Single Large Or Several Small”), which considers whether it is better to conserve single large or several small fragments of a habitat. Small fragments are expected to cover greater habitat heterogeneity due to a larger geographical distance and thereby greater total species richness, whereas large fragments offer more stable habitat conditions and bigger population sizes. In this study, in addition to plants and leafhoppers, we also collected data on true bugs and snails. Species richness of all four taxa as well as the richness of habitat specialists was substantially higher on several small fragments than on one or two large fragments of equal total size. However, community composition of large and small fragments differed and some of the rarest specialist species were confined to large fragments. The complexity of the landscape surrounding the fragments did not play an important role for species richness and community composition. These results question the focus on either small or large fragments and imply that both large and small habitat fragments are needed for successful biodiversity conservation. In the third part of the thesis, we explore the effects of grassland management (grazing, mowing and abandonment), connectivity and landscape composition on species richness, abundance, community composition and trait-based responses (body size and Red List status) of nine taxa: plants, butterflies, bees, grasshoppers, hoverflies, spiders, true bugs, rove beetles and leafhoppers. We selected 30 small fragments (<1 ha) of calcareous grassland along orthogonal gradients of habitat connectivity and landscape complexity. We found a negative effect of an increasing percentage of arable land in the surroundings of the fragments, which led to a 29 % loss of overall species richness. We presume that landscapes dominated by arable land offer less alternative habitat and resources for foraging or during migration, resulting in lower species richness. Habitat connectivity generally enhanced species richness across all taxa. This was more accentuated in the large species per taxon, which can be expected to be good dispersers. Finally, grazing reduced species richness and abundance much more than mowing (once a year) or short-term abandonment (for 5-15 years), in particular of red-listed species, presumably due to the greater damage caused, reducing food resources for phytophagous insects. Furthermore, each of the three management types resulted in a different community composition of all taxa. Therefore, the preferential management strategy for small fragments of calcareous grassland should be an alternation between mowing and short-term abandonment combined with a diversification of the surrounding landscape. Overall, we conclude that the widespread concentration on large habitat fragments should be reconsidered, leading to the conservation of both large and small habitat fragments. When planning conservation measures for fragmented grassland habitats, a focus on local factors like fragment size and management is important but insufficient: landscape factors including habitat connectivity and landscape complexity need to be taken into account to ensure the long-term survival of specialised plant and invertebrate populations

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

Abstract Herbivory 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

Context Global change pressures (GCPs) imperilspecies 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. Objectives 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. Methods 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). Results We found synergistic, conservation relevant effects: Connectivity boosted the proportion of redlisted 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. Implications 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

Resolving the SLOSS dilemma for biodiversity conservation: a research agenda

The legacy of the ‘SL > SS principle’, that a single or a few large habitat patches (SL) conserve more species than several small patches (SS), is evident in decisions to protect large patches while down-weighting small ones. However, empirical support for this principle is lacking, and most studies find either no difference or the opposite pattern (SS > SL). To resolve this dilemma, we propose a research agenda by asking, ‘are there consistent, empirically demonstrated conditions leading to SL > SS?’ We first review and summarize ‘single large or several small’ (SLOSS) theory and predictions. We found that most predictions of SL > SS assume that between-patch variation in extinction rate dominates the outcome of the extinction–colonization dynamic. This is predicted to occur when populations in separate patches are largely independent of each other due to low between-patch movements, and when species differ in minimum patch size requirements, leading to strong nestedness in species composition along the patch size gradient. However, even when between-patch variation in extinction rate dominates the outcome of the extinction–colonization dynamic, theory can predict SS > SL. This occurs if extinctions are caused by antagonistic species interactions or disturbances, leading to spreading-of-risk of landscape-scale extinction across SS. SS > SL is also predicted when variation in colonization dominates the outcome of the extinction–colonization dynamic, due to higher immigration rates for SS than SL, and larger species pools in proximity to SS than SL. Theory that considers change in species composition among patches also predicts SS > SL because of higher beta diversity across SS than SL. This results mainly from greater environmental heterogeneity in SS due to greater variation in micro-habitats within and across SS habitat patches (‘across-habitat heterogeneity’), and/or more heterogeneous successional trajectories across SS than SL. Based on our review of the relevant theory, we develop the ‘SLOSS cube hypothesis’, where the combination of three variables – between-patch movement, the role of spreading-of-risk in landscape-scale population persistence, and across-habitat heterogeneity – predict the SLOSS outcome. We use the SLOSS cube hypothesis and existing SLOSS empirical evidence, to predict SL > SS only when all of the following are true: low between-patch movement, low importance of spreading-of-risk for landscape-scale population persistence, and low across-habitat heterogeneity. Testing this prediction will be challenging, as it will require many studies of species groups and regions where these conditions hold. Each such study would compare gamma diversity across multiple landscapes varying in number and sizes of patches. If the prediction is not generally supported across such tests, then the mechanisms leading to SL > SS are extremely rare in nature and the SL > SS principle should be abandoned

Auchenorrhyncha and Psylloidea collected during the 25th Central European Auchenorrhyncha meeting, Arnhem, The Netherlands (Hemiptera: Auchenorrhyncha and Psylloidea)

Die 25. Mitteleuropäische Zikadentagung fand vom 14.-17. September 2018 in Arnheim in den Niederlanden statt. Da es die erste Tagung in den Niederlanden war, wurden Sammelexkursionen in fünf typische niederländische Landschaften unternommen. Drei der Exkursionsziele befanden sich in neu geschaffenen Schutzgebieten, die sich auf ehemals landwirtschaftlich genutzten Flächen befinden. Die beiden weiteren Exkursionsziele waren alte, geschützte Heideflächen. Insgesamt konnten 117 Zikadenarten und 6 Psylloidea-Arten nachgewiesen werden. Drei Arten waren neu für die Niederlande: Macrosteles spinosus (in dieser Publikation vorgestellt), Kybos abstrusus (monophag an Populus nigra) und Macrosteles sardus (an Epilobium hirsutum). Für einige seltene Arten konnten neue Fundpunkte ermittelt werden: Kelisia monoceros, Aphrophora major, Stroggylocephalus agrestis, Edwardsiana diversa, E.&nbsp;tersa, Fruticidia bisignata, Ophiola russeola und Psammotettix pallidinervis. Durch die drei Neufunde erhöht sich die Anzahl der bislang in den Niederlanden nachgewiesenen Zikadenarten auf 421. Diese Arbeit zeigt zudem, dass selbst in erst seit kurzem bestehenden Schutzgebieten seltene und interessante Arten nachgewiesen werden können.&nbsp;The 25th Central European Auchenorrhyncha meeting took place in Arnhem, The Netherlands on 14-17 September 2018. It was the first time the meeting was held in The Netherlands, and for this reason, excursions were undertaken to five typical Dutch landscapes. Three of the excursions involved newly created nature reserves, located on former agricultural land. The other two were old, protected heathlands. In total, 115 Auchenorrhyncha species, and 6 Psylloidea species were collected. Three species were new for the Netherlands: Macrosteles spinosus (presented in this paper), Kybos abstrusus (monophagous on Populus nigra) and Macrosteles sardus (Epilobium hirsutum). For a number of rare species new occurrences were reported: Kelisia monoceros, Aphrophora major, Stroggylocephalus agrestis, Edwardsiana diversa, E. tersa, Fruticidia bisignata, Ophiola russeola and Psammotettix pallidinervis. Our results show that also in young, newly created nature reserves interesting species can be found.&nbsp

Leafhopper diversity in home gardens – results of a survey in four countries across Europe (Hemiptera, Auchenorrhyncha)

Despite urbanisation being one of the main drivers of habitat destruction and biodiversity loss, home gardens can provide habitat for a wide range of species. Here we report the results of a leafhopper survey in 12 gardens in four European countries (Germany, Serbia, Austria and Bulgaria). Sampling was conducted in a semi-standardised way across the summer 2020. In total, 143 Auchenorrhyncha species with 2,361 adult specimens were recorded, including several red-listed species. The number of species per garden varied between 9 and 58. On average, around 26 species were found. Leafhopper diversity was positively influenced by garden area, age, plant diversity, extensive management and the cover of forests and parks in the surroundings, but also by the number of sampling dates. We conclude that extensively managed home gardens across Europe can support diverse communities of leafhoppers which is crucial in times of severe insect declines

The Auchenorrhyncha fauna of the nutrient-poor acidic meadows and pastures of the Haigerach valley in the western Black Forest (Baden-Württemberg, Germany)

In den Jahren 2019 und 2020 wurden sieben bodensaure Magerwiesen und -weiden im Haigerachtal im westlichen Schwarzwald (Baden-Württemberg) auf ihre&nbsp;Zikadenfauna hin untersucht. Insgesamt wurden 1.744 Individuen aus 63 Arten erfasst. 15&nbsp;dieser Arten (24 %) stehen auf der aktuellen Roten Liste der Zikaden Deutschlands, darunter&nbsp;bemerkenswerte Arten wie Sardius argus, Tettigometra virescens, T. impressopunctata, Ribautodelphax&nbsp;collina, Kelisia monoceros und Goniagnathus brevis. Für diese Indikatoren historisch alter&nbsp;Weidelandschaften („pascuophile“ Arten) ist es wichtig, dass eine extensive Bewirtschaftung&nbsp;durch Beweidung mit Rindern oder Schafen fortgeführt wird.In 2019&nbsp;and 2020 Auchenorrhyncha were sampled on seven nutrient-poor acidic meadows and pastures&nbsp;in the Haigerach valley in the western Black Forest. In total 1.744 specimens belonging&nbsp;to 63 species were collected. Among these, 15 species (24 %) are listed as vulnerable or threatened&nbsp;in the Red List of Auchenorrhyncha species of Germany, among them remarkable species&nbsp;like Sardius argus, Tettigometra virescens, T. impressopunctata, Ribautodelphax collina, Kelisia&nbsp;monoceros and Goniagnathus brevis. These species are indicators of historically old grazing&nbsp;landscapes and therefore depend on the continuation of extensive management through grazing&nbsp;by cattle or sheep

Increase in breeding bird abundance and diversity with semi-natural habitat in vineyard landscapes.

Agricultural expansion and intensification are major threats to biodiversity, and even some once common farmland bird species are now endangered. Wine-growing landscapes are intensively managed but can still be an attractive habitat for a wide range of species. However, only few bird species breed within vineyards and thus, semi-natural habitat types like hedges, woodland patches and grasslands are crucial for bird populations. We investigated how birds breeding in wine-growing areas are influenced by the surrounding landscape at three spatial scales: territories, sampling transects and landscapes. In the German wine growing region Palatinate, sixteen landscapes with a radius of 500 m were chosen spanning a gradient in the cover of semi-natural habitat. Bird territories were mapped along three transects of 500 m length in each landscape. We found 300 territories of 33 bird species. Positive effects of semi-natural habitat cover on birds were strongest at the transect scale, with almost proportional increase of species and territory numbers with the cover of semi-natural habitat. Most bird species selected territories that contained more semi-natural habitat than the landscape-wide average of 13.5%, but e.g. woodlark and linnet showed an opposite preference. In addition, the birds' community composition was influenced by the composition of the surrounding landscape. Most species were associated with semi-natural habitat types or built-up areas while vineyards had hardly any species associated with them. Our results suggest that in wine-growing landscapes, the decline in farmland birds can be reversed by the re-establishment of hedges, trees, woodland patches, traditional orchards and grassland areas. However, as preferences at the territory scale were species-specific, there is no uniform best solution for bird conservation in viticultural landscapes. Thus, landscape development should always be accompanied by experts that take the demands of existing and potential breeding birds into account