Arthropods in linear elements Occurrence, behaviour and conservation management Thesis committee Thesis supervisor: Prof. dr. Karlè V. Sýkora Professor of Ecological Construction and Management of Infrastructure Nature Conservation and Plant Ecology Group Wageningen University Thesis co‐supervisor: Dr. ir. André P. Schaffers Scientific researcher Nature Conservation and Plant Ecology Group Wageningen University Other members: Prof. dr. Dries Bonte Ghent University, Belgium Prof. dr. Hans Van Dyck Université catholique de Louvain, Belgium Prof. dr. Paul F.M. Opdam Wageningen University Prof. dr. Menno Schilthuizen University of Groningen This research was conducted under the auspices of SENSE (School for the Socio‐Economic and Natural Sciences of the Environment) Arthropods in linear elements Occurrence, behaviour and conservation management Jinze Noordijk Thesis submitted in partial fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. dr. M.J. Kropff, in the presence of the Thesis Committee appointed by the Doctorate Board to be defended in public on Tuesday 3 November 2009 at 1.30 PM in the Aula Noordijk J (2009) Arthropods in linear elements – occurrence, behaviour and conservation management Thesis, Wageningen University, Wageningen NL with references, with summaries in English and Dutch ISBN 978‐90‐8585‐492‐0 C’est une prairie au petit jour, quelque part sur la Terre. Caché sous cette prairie s’étend un monde démesuré, grand comme une planète. Les herbes folles s’y transforment en jungles impénétrables, les cailloux deviennent montagnes et le plus modeste trou d’eau prend les dimensions d’un océan. Nuridsany C & Pérennou M 1996. Microcosmos, Le peuple de l’herbe. Galatée Film – France 2 Cinéma. ‘De natuur biedt toch altijd een aangename verkwikking,’ sprak Erik, opgewekt rondziend, ‘en stelt zelden teleur.’ [...] ‘Zeer juist,’ sprak de mier, die naast hem liep, hem enigszins schichtig aankijkend, ‘u slaat daar den spijker wel op den kop.’ Bomans G 1941. Erik of het klein insectenboek. Het Spectrum, Utrecht. ABSTRACT Intensification of agriculture and urbanisation have caused large‐scale destruction and fragmentation of natural and semi‐natural areas in the Netherlands, with a considerable loss of biodiversity. As a consequence, the conservation of the biodiversity in the remaining small landscape elements has become increasingly urgent. This thesis presents the results of our study of arthropods in (mainly) roadside verges. The diversity of species proved to be considerable, with several rare and threatened, as well as many specialised species. These arthropod assemblages should be taken into account during the management of roadside verges. Our research aimed at a better understanding of the distribution and ecology of these species, which enables us to recommend appropriate measures for their conservation. Roadside verges are often covered by grassland vegetation and need to be mown in order to retain a high biodiversity. We studied ground beetles, weevils, ants and epigeic spiders in experimental plots with five different mowing regimes: no mowing; mowing once a year in autumn with or without removal of the cuttings; mowing twice a year, in early summer and autumn, with and without removal of the cuttings. Plots were located on three different verges which represented a plant productivity gradient, ranging from low‐productive, through medium‐productive to high‐productive grassland. The different mowing regimes had hardly any effect on the biodiversity at the low‐productive site, whereas at the medium‐productive and high‐productive sites, mowing twice a year with removal of the cuttings resulted in the highest arthropod species‐richness and abundance. A second experiment carried out on the medium‐productive verge showed that mowing twice a year with removal of the cuttings also gave the highest values for flower richness, flower diversity and abundance of flower‐visiting insects. Therefore such verges also had the highest number of visits to flowers by insects. On low‐productive verges, yearly mowing is not necessary. However, to ensure a high diversity of arthropods on medium‐productive to high‐ productive grassland verges, a regime of mowing twice a year with removal of cuttings is recommended for the largest part of the verge. Small patches of vegetation should be left intact to provide a refuge for arthropods in the period just after mowing when their resources are otherwise almost absent. This type of rotational management will probably improve their chance of survival. Sandy verges can be important to xerophilic and thermophilic arthropods. These species are in decline due to the fragmentation and decreasing quality of heathland nature reserves. In the past, habitats for these species were numerous in the roadside verges in the Veluwe area. However, now vegetation succession is causing them to disappear and restoration management is urgently needed. We sampled arthropods in patches of grey hair‐grass (Corynephorus canescens) vegetation on the verges, and found that there were fewer stenotopic ground beetles and spiders than in similar vegetation patches in nature reserves. This seems attributable to differences in ‘habitat quality’, namely a denser cover of grass in the verges, as well as more herbaceous plants and tree seedlings. Moreover, any suitable vegetation patches are smaller. In addition, we sampled ground‐dwelling and flying ground beetles in open sandy roadside verges and newly‐created linear forest clearings. The occurrence of teneral individuals and flightless species indicate that verges may function as ‘habitat corridors’. In the forest clearings, teneral individuals were rare, but flying beetles were very abundant: more than twice as many individuals were caught here than in nature reserves and on roadside verges. This indicates that the clearings are used particularly by dispersing ground beetles, and thus function mainly as ‘movement corridors’. To make conditions more suitable for xerophilic and thermophilic species in roadside verges, we recommend restoring nutrient‐poor zones and recreating pioneer conditions. Subsequently, a regular management of selectively removing encroaching vegetation should be installed. If this is done over large distances, roadside verges can act as habitat corridors. Linear clearings in forests, situated between separate heathland habitat areas can help species bridge short distances between them. In this way, ecological networks can be created in highly fragmented heathland landscapes. Being relatively straight and narrow, roadside verges have an enormous distance of edge biotopes. We therefore studied edge effects on insect species to obtain more insight into how a verge functions as a habitat. We looked at the effects of the border between the vegetation and asphalt of the road on the direction of movement of two ground beetle species. The road appeared to be a barrier for these species and its presence caused movement patterns parallel to the asphalt. In another study, the number of flying ground beetles increased in linear forest clearings, probably because they are directed by forest edges when dispersing. Both studies provide extra evidence that roadside verges may act as ecological corridors. In addition, we found that flying ants used forest edges to find each other for mating, while their nests were located elsewhere. All these results indicate a substantial effect of edges on insect behaviour and their occurrence. This knowledge can be applied in conservation management. Roadside verges are distinctive biotopes with anthropogenic disturbances and edge effects that may negatively influence arthropods. However, as roads are an inherent, inevitable part of the densely populated Netherlands landscape, we choose here to emphasise the positive aspects of these linear habitats. Our investigations show that arthropod communities of high conservation interest occur in roadside verges, that verges can be used to create ecological networks, that abrupt biotope edges in verges act as a guide for dispersing insects and are sometimes favoured as a mating site, and that a regular applied mowing scheme provides valuable conditions for arthropods of hay‐meadows. Contents INTRODUCTION 1. General introduction 13 2. Arthropod richness in roadside verges in the Netherlands 23 MANAGEMENT OF GRASSLAND VERGES FOR ARTHROPODS 3. Effects of vegetation management by mowing on epigeic arthropods 39 4. Optimizing grassland management for flower‐visiting insects in roadside verges 61 A LANDSCAPE APPROACH TO ARTHROPODS IN SANDY VERGES 5. Diversity of ground beetles and spiders in roadside verges with grey hair‐grass vegetation 79 6. Habitat and movement corridors to improve landscape connectivity for heathland carabids 97 INSECT BEHAVIOUR IN LINEAR ELEMENTS 7. Impact of a road on the movements of two ground beetle species 119 8. How ants find each other; temporal and spatial patterns in nuptial flights 133 DISCUSSION AND RECOMMENDATIONS FOR MANAGEMENT 9. General discussion 149 Summary 165 Samenvatting 169 Dankwoord 175 Curriculum vitae 179 SENSE educational PhD programme 185 1 GENERAL INTRODUCTION Arthropod conservation The global decline in species concerns all life forms. Arthropods comprise the absolute majority of organisms (May 1992), so it can be concluded that also the majority of the extinctions concerns this group (Dunn 2005). In addition, there are indications that insects, a major group within