Our review looks at pollinator conservation and highlights the differences in approach between managing for pollination services and preserving pollinator diversity. We argue that ecosystem service management does not equal biodiversity conservation, and that maintaining species diversity is crucial in providing ecosystem resilience in the face of future environmental change. Management and policy measures therefore need to focus on species not just in human dominated landscapes but need to benefit wider diversity of species including those in specialised habitats. We argue that only by adopting a holistic ecosystem approach we can ensure the conservation and sustainable use of biodiversity and ecosystem services in the long-term.

Our review looks at pollinator conservation and highlights the differences in approach between managing for pollination services and preserving pollinator diversity. We argue that ecosystem service management does not equal biodiversity conservation, and that maintaining species diversity is crucial in providing ecosystem resilience in the face of future environmental change. Management and policy measures therefore need to focus on species not just in human dominated landscapes but need to benefit wider diversity of species including those in specialised habitats. We argue that only by adopting a holistic ecosystem approach we can ensure the conservation and sustainable use of biodiversity and ecosystem services in the long-term.

An increasing degree of attention is being given to the ecosystem services which insect pollinators supply, and the economic value of these services. Recent research suggests that a range of factors are contributing to a global decline in pollination services, which are often used as a “headline” ecosystem service in terms of communicating the concept of ecosystem services, and how this ties peoples׳ well-being to the condition of ecosystems and the biodiversity found therein. Our paper offers a conceptual framework for measuring the economic value of changes in insect pollinator populations, and then reviews what evidence exists on the empirical magnitude of these values (both market and non-market). This allows us to highlight where the largest gaps in knowledge are, where the greatest conceptual and empirical challenges remain, and where research is most needed.

Natural Capital, and the ecosystem services derived from it, are essential to human well-be-ing and economic prosperity. Indeed, nature inspires and provides many solutions that can help us tackle some of the most pressing challenges of our time. For example, pollinators matter because a majority of European crops depend or benet from insect pollination. Another example is the contribution of pollinators to preserving cherished natural and cultural landscapes through wildower pollination. However, due to a cocktail mix of drivers of change, pollinator species are disappearing and pollinator populations are declining. ese losses accentuate several of our societal chal-lenges, including food security and ecosystem degradation. Hence, building knowledge on the causes behind pollinator decline, and the eects of pollinator decline on other species and ecosystems is essential. e STEP project has contributed signicantly within this eld, with a particular focus on the status and drivers behind trends in European pollinators.Furthermore, research into the dierent solutions for maintaining or enhancing pollinator populations is crucial. ese activities enrich the knowledge base on Nature-based solu-tions, solutions that are inspired by or supported by nature and address societal challenges while maintaining or enhancing our natural capital. Overall, research and innovation ac-tions such as those successfully supported by the STEP project, contribute to greening the economy and making development sustainable.

1. The role of nocturnal moths within plant-pollinator networks is poorly understood but could be important in the context of declining biodiversity and the ecosystem services they provide. 2. For the first time, this study examined the role of moths as pollen vectors in the Mediterranean Biodiversity Hotspot. Light traps were used to sample moths in SW Portugal in 2010. The pollen on moth head parts was collected, identified, and counted to construct a nocturnal pollen-transfer and flower-visitor network. 3. A total of 257 moths belonging to 95 species were captured in 11 trapping sessions in 2010; 196 moths (76%) carried pollen and the total number of pollen grains counted and identified was 9064. 4. The pollen-transfer network exhibited a high degree of selectivity (H20) but low robustness when the most-to-least connected plants were made extinct in the network. The flower-visitor network (based on the incidences of interactions by individual moths), however, exhibited high linkage density and was generally more robust to simulated plant or moth extinction. 5. Including nocturnal moths in plant–pollinator networks will provide a better understanding of their robustness to species extinctions due to environmental change as well as the impacts on ecosystem structure and functioning. Nocturnal pollen–transfer networks could be developed for identifying key species for targeted conservation.

Bioenergy forestry is a viable alternative to fossil fuels, providing a mean to reduce net carbon emissions and thus our impact on climate change. It is therefore important that bioenergy production is not hampered by herbivory. If plants with certain traits can be chosen to maximize biological control, bioenergy forestry can become an even more potent and sustainable practice. The aim of my project is to investigate what effects sex in a bioenergy crop has on multitrophic interactions and pollinator attraction. Plant sex effects will be investigated using the dioecious Salix viminalis (Salicaceae), commonly grown in plantations in Sweden, Germany, Denmark, Great Britain and a few more European countries. The project will describe how plant sex affects ecosystem services provided by this crop (biological control and pollination), and through that the potential to increase these ecosystem services through selecting or combining clones of either sex. While the results will be easily applied knowledge, my project will also expand our general knowledge of plant sex effects; multitrophic interactions between plants and insects and among insects are barely described. Insect species under study will be a herbivorous beetle (Phratora vulgatissima, Coleoptera), an omnivorous predatory bug (Anthocoris nemorum, Hemiptera), and a parasitoid wasp (Perilitus brevicollis, Hymenoptera). I will use these species in a series of field- and laboratory based experiments. In addition, plant sex effects on pollinator attraction will be tested in the field experiments through observing flower visitation rates and recording berry production in adjacent woodland strawberries, Fragaria vesca. The aim of this essay is to compile (i) an overview of previous work performed on, or otherwise relevant to, plant sex effects on interactions with animals and (ii) necessary information on the study system that I will use in the planned experiments.

Tropical countries contribute substantially to global agricultural production, but the majority of farmers are small-scale subsistence farmers. Their comparably low agricultural productivity is coupled with major yield gaps. Agricultural expansion and the intensive use of agro-chemicals are the major cause for the destruction of tropical habitats and biodiversity loss and pose a threat to ecosystem services. However, many tropical small-holder farmers rely on ecosystem services like insect pollination or natural pest control, which may play an indispensable role in closing yield gaps. In addition, losses from pollination deficits or pest pressure are usually mitigated by the use of managed pollinators or pesticides that in turn can be harmful to ecosystem services provided by wild insects. We aim to shed light on the relative importance of pollination services, common management practices and their interaction. We evaluated the benefits from pollination services for cucumber (Cucumis sativus) production and how wild bees (the main cucumber pollinators in the region) are influenced by management on four different spatial scales. We furthermore assessed income loss due to dis-services from seed predating ants in order to suggest management measures that may reduce yield gaps. Our work comprises experimental field studies on small-scale vegetable production in homegardens in tropical central Sulawesi, Indonesia and a review on pollination services to highlight existing information and to close information gaps on pollinations services for crops. In the first study (chapter 2) we tested how different management practices (insect pollination, weed control, fertilization and herbivore control) affect cucumber fruit set and yield and how these variables influence each other. We found that insect pollination, fertilization and weed control increased crop fruit set and yield in an additive way. However, fertilization and weed control alone could not compensate for pollination loss, which was the most important driver and accounted for 75 % of the yield. We found an interaction between the weed control and pollination treatment in which weed control strongly influenced insect-pollinated plants but not wind and self-pollinated plants. This indicates that weed control contributes to closing yield gaps, but only in addition to insect pollination. In contrast, insecticides to control herbivores did not influence yield. We recommend shifting the focus from common management practices towards more sustainable management to enhance pollination services and stress the importance for policy driven regulations of reduced and better targeted pesticide application in tropical agroecosystems. In the second study (chapter 3), we evaluated variables from three spatial scales to better understand bee communities indispensable for cucumber production. We further assessed if the response to these scale predictors depends on pollinator body size and sociality. Yield increased significantly with increasing number of flower-visiting bee individuals (mainly composed of wild solitary bees which translates into a net income decline of 47% if half of the bees would be lost. For optimized bee management, farmers need to consider four spatial scales. On the garden scale (1), the homegarden-wide percentage of flower cover predicted pollinator attraction best, if, on the adjacent-habitat scale (2), a higher percentage of homegardens (at least 20%, best 50% in a 200m radius) surrounded the study garden. In addition, the landscape scale (3), distance to the rainforest (up to 2.2 km) had also a significant effect on total bee flower visitor. This effect was dominated by small bees which increased closer to the forest. We conclude that farmers need to adjust bee management accordingly to reduce major yield gaps. High percentages of crops and non-crop plants flowering inside the homegarden can attract pollinators from adjacent source habitats that are mainly homegardens as well. In the third study (chapter 4), we aimed to assess the effect of seed predation by ants on sown seeds of four crop species (C. sativus, Daucus carota, Capsicum frutescens and Solanum melongena) and the resulting impact on the net income of small-scale farmers. Furthermore, we tested if ant seed predation differs with or without insecticide and herbicide applications. We found that ant seed predation was high for all crops (42.0 %, 49.4 %, 48.0 % and 50.6 % for C. sativus, D. carota, C. frutescens and S. melongena, respectively), potentially reducing farmers’ net income by half. Application of insecticides and herbicides did not influence ant seed predation or total ant abundance, but influenced ant species-specific abundances positively or negatively. Despite ant species-specific responses to insecticide and herbicide applications, we found consistently high seed predation rates across all gardens. We conclude that high seed predation is caused by high overall ant abundance mediated through functional redundancy of ant species. We recommend more environmentally friendly and sustainable practices such as overseeding or seedling production in nurseries to reduce chemical pest control. In the fourth study (chapter 5), we reviewed pollination services and their importance to crops focusing on another understudied geographical region - the Neotropics - to get an overview of the main pollinator taxa and the dependence on pollination services of crops. In addition, we summarized pollination research methodologies and discuss pollination relevant farm and landscape management, as well as socio-economic drivers affecting pollination services. We have shown that pollination services by wild pollinators are important for crop production. However, knowledge gaps exist in terms of the quantity, quality and stability of crop production provided by animal pollinators. It is also critical to understand how multiple socioeconomic drivers influence the selection of particular management systems and, thus, the environmental services delivered. In conclusion, pollination services are of major importance for closing yield gaps in tropical small-scale agriculture, such as homegardens. Although common management practices such as the use of agro-chemicals influence yield, they do not compensate yield gaps due to pollinator loss or ant seed predation. The enhancement of pollination services should be considered as well as the reduction of pesticide use in the majority of tropical agroecosystems. Farmers should adapt environmentally friendly and more sustainable practices adjusted to bee management considering four spatial scales to reduce major yield gaps.

Magistritöö teema on seotud europrojektiga QuESSA (i.k. Quantification of Ecosystem Services for Sustainable Agriculture; e.k. Ökosüsteemi teenuste roll jätkusuutlikus põllumajanduses). Uurimistöö eesmärkideks oli välja selgitada, kas ja kuidas mõjutavad erinevad maastikuelemendid tolmeldajate arvukust ja taksonoomilist koosseisu ning kas see sõltub püsivate maastikuelementide rohkusest. Käesoleva töö käigus, uuriti kasutades vesipüüniste meetodit, millised tolmeldajate rühmad esinevad erinevate looduslike alade osakaaludega maastikul asuvatel rapsipõldudel ja nendega piirnevatel maastikuelementidel. Andmete kogumine toimus 2014. a. Tartumaal talirapsi tootmispõldudel ja nendega piirnevatel maastikuelementidel. Selleks valiti 18 ühe kilomeetrise raadiusega prooviala, mille keskel asus talirapsi põld. Vaatlusalused maastikuelemendid, mis piirnesid vahetult vaatlusala keskel asuva rapsipõlluga olid lineaarne rohtne põlluserv, lineaarne puudega põlluserv ehk puiskoridor ja kontroll-ala. Entomoloogilise materjali kogumiseks kasutati vesipüüniseid, mis asetsesid rohtse taimestiku kõrgusel. Rapsipõllu sisse paigutati kollased vesipüünised ja põlluga piirnevatele maastikuelementidele kollased, sinised ja valged vesipüünised. Kogu katseperioodi jooksul korjati vesipüünistest kokku 2014 erinevat tolmeldajat. Kimalasi leiti vesipüünistest kokku 124, erakmesilasi 1577, meemesilasi 156 ja sirelasi 157 isendit. Antud katse käigus olid maastikuelementidel ja põllumajandusmaastikul arvukamad kimalaste liigid aed-, metsa-, põldja kivikimalane. Meemesilaste ja sirelaste arvukuse puhul leiti mõju püünise värvi suhtes. Kõigile katses uuritud tolmeldajate arvukusele avaldas positiivset mõju puiskoridor. Erakmesilaste arvukus oli väikseim rapsipõldudel, mis piirnesid teise mitteõitseva kultuurpõlluga. Looduslike alade osakaal ei mõjutanud kimalaste ega meemesilaste arvukust ei põllul ega ka põlluga piirneval maastikuelemendil. Sirelaste arvukus maastikuelemendil sõltus aga oluliselt looduslike alade osakaalust. Püünise kaugus põlluservast mõjutas erakmesilaste arvukust. Katsematerjali kogumise aeg mõjutas nii maastikuelemendilt kui ka põllult püütud kimalaste, erakmesilaste, sirelaste ja meemesilaste arvukust. | This Master´s thesis is a part of the project QuESSA (Quantification of Ecosystem Services for Sustainable Agriculture; Ökosüsteemi teenuste roll jätkusuutlikus põllumajanduses). The research aims were to determine whether and how different landscape elements affect pollinator abundance and taxonomic composition and whether these depend on the percentage of permanent natural areas. Different pollinator groups were assessed in winter oilseed rape fields and in their adjacent landscape elements with a pan trap method in landscapes with different percentages of natural areas. Data collection took place in Tartumaa in May 2014 in 18 landscape sectors of one kilometer radius each with a winter oilseed rape field in the middle (focal field). The focus side of each focal field was directly bordered by either a linear element (grass strip) or a woody linear element (line of scrub, hedge or trees) or with another field with a different crop. The entomological material was collected using pan traps, which were placed lower than the height of the vegetation. There were 4 yellow pan traps in each oilseed rape field and two sets of yellow, blue and white pan traps in the adjacent landscape elements. Throughout the study, a total of 2014 different pollinators were caught with pan traps: 124 bumblebees, 1577 solitary bees, 156 honey bees and 157 hoverflies. The most numerous bumblebee species were B. hortorum, B. sylvarum, B. pascuorum and B. lapidaries. Honey bee and hoverfly abundance was affected by the colour of the trap. Woody linear elements had a positive influence on the abundance of all studied pollinator groups. Solitary bee abundance was the lowest in rape fields bordered by another non flowering crop field. The percentage of natural areas did not affect the abundance of bumblebees and honey bees in rape fields and in adjacent landscape elements. The abundance of hoverflies depended on the percentage of natural areas. The distance of traps from the field edge affected the abundance of solitary bees. Sampling time influenced the abundance of bumblebees, solitary bees, hoverflies and honey bees in landscape elements as well as in fields.

Magistritöö teema on seotud europrojektiga QuESSA (i.k. Quantification of Ecosystem Servicesfor Sustainable Agriculture; e.k. Ökosüsteemi teenuste roll jätkusuutlikus põllumajanduses).Uurimistöö eesmärkideks oli välja selgitada, kas ja kuidas mõjutavad erinevadmaastikuelemendid tolmeldajate arvukust ja taksonoomilist koosseisu ning kas see sõltubpüsivate maastikuelementide rohkusest. Käesoleva töö käigus, uuriti kasutades vesipüünistemeetodit, millised tolmeldajate rühmad esinevad erinevate looduslike alade osakaaludegamaastikul asuvatel rapsipõldudel ja nendega piirnevatel maastikuelementidel. Andmetekogumine toimus 2014. a. Tartumaal talirapsi tootmispõldudel ja nendega piirnevatelmaastikuelementidel. Selleks valiti 18 ühe kilomeetrise raadiusega prooviala, mille keskel asustalirapsi põld. Vaatlusalused maastikuelemendid, mis piirnesid vahetult vaatlusala keskel asuvarapsipõlluga olid lineaarne rohtne põlluserv, lineaarne puudega põlluserv ehk puiskoridor jakontroll-ala. Entomoloogilise materjali kogumiseks kasutati vesipüüniseid, mis asetsesid rohtsetaimestiku kõrgusel. Rapsipõllu sisse paigutati kollased vesipüünised ja põlluga piirnevatelemaastikuelementidele kollased, sinised ja valged vesipüünised. Kogu katseperioodi jooksulkorjati vesipüünistest kokku 2014 erinevat tolmeldajat. Kimalasi leiti vesipüünistest kokku 124,erakmesilasi 1577, meemesilasi 156 ja sirelasi 157 isendit. Antud katse käigus olidmaastikuelementidel ja põllumajandusmaastikul arvukamad kimalaste liigid aed-, metsa-, põldjakivikimalane. Meemesilaste ja sirelaste arvukuse puhul leiti mõju püünise värvi suhtes. Kõigilekatses uuritud tolmeldajate arvukusele avaldas positiivset mõju puiskoridor. Erakmesilastearvukus oli väikseim rapsipõldudel, mis piirnesid teise mitteõitseva kultuurpõlluga. Looduslike alade osakaal ei mõjutanud kimalaste ega meemesilaste arvukust ei põllul ega ka põllugapiirneval maastikuelemendil. Sirelaste arvukus maastikuelemendil sõltus aga oluliselt looduslikealade osakaalust. Püünise kaugus põlluservast mõjutas erakmesilaste arvukust. Katsematerjalikogumise aeg mõjutas nii maastikuelemendilt kui ka põllult püütud kimalaste, erakmesilaste,sirelaste ja meemesilaste arvukust. | This Master´s thesis is a part of the project QuESSA (Quantification of Ecosystem Services forSustainable Agriculture; Ökosüsteemi teenuste roll jätkusuutlikus põllumajanduses). Theresearch aims were to determine whether and how different landscape elements affect pollinatorabundance and taxonomic composition and whether these depend on the percentage of permanentnatural areas. Different pollinator groups were assessed in winter oilseed rape fields and in theiradjacent landscape elements with a pan trap method in landscapes with different percentages ofnatural areas. Data collection took place in Tartumaa in May 2014 in 18 landscape sectors of onekilometer radius each with a winter oilseed rape field in the middle (focal field). The focus sideof each focal field was directly bordered by either a linear element (grass strip) or a woody linearelement (line of scrub, hedge or trees) or with another field with a different crop. Theentomological material was collected using pan traps, which were placed lower than the height ofthe vegetation. There were 4 yellow pan traps in each oilseed rape field and two sets of yellow,blue and white pan traps in the adjacent landscape elements. Throughout the study, a total of2014 different pollinators were caught with pan traps: 124 bumblebees, 1577 solitary bees, 156honey bees and 157 hoverflies. The most numerous bumblebee species were B. hortorum, B.sylvarum, B. pascuorum and B. lapidaries. Honey bee and hoverfly abundance was affected bythe colour of the trap. Woody linear elements had a positive influence on the abundance of allstudied pollinator groups. Solitary bee abundance was the lowest in rape fields bordered byanother non flowering crop field. The percentage of natural areas did not affect the abundance ofbumblebees and honey bees in rape fields and in adjacent landscape elements. The abundance ofhoverflies depended on the percentage of natural areas. The distance of traps from the field edgeaffected the abundance of solitary bees. Sampling time influenced the abundance of bumblebees,solitary bees, hoverflies and honey bees in landscape elements as well as in fields.

Thesis (MSc)--Stellenbosch University, 2015. | ENGLISH ABSTRACT: Our planet is in the midst of a biodiversity crisis, with factors such as land transformation, climate change, anthropomorphic disturbance and invasive species acting together to threaten biodiversity. In South Africa, with minimal natural wood resources, commercial forestry is one of the most abundant forms of landscape transformation. However, a third of the land inside many plantations has been set aside for conservation as unplanted remnant grassland patches (RGPs). These areas are subjected to an additional negative impact by invasive alien species, namely Rubus cuneifolius (American bramble), a weed that is particularly problematic in and around forestry plantations in South Africa. The grassland biome of South Africa is extremely diverse and is of vital importance for the ecosystem services it supplies. Despite this, the grassland biome is under threat as this is where much of South Africa’s forestry plantations are located. Driven by anthropomorphic disturbance, pollinators are in decline. Landscape transformation of natural areas for forestry plantations is likely to affect plant-pollinator interactions which will affect ecosystems and biodiversity. However, it is not known to what extent these ecosystems are affected. It is thought that the impact depends on the complexity of the ecosystem in question, and analyses at the network-level provide insights into the robustness of ecosystems in the face of biodiversity loss. Thus, this study evaluates the effect of natural habitat fragmentation and invasion of the alien species, R. cuneifolius, on flower visitation networks of South African grasslands. The study was conducted in the KwaZulu-Natal Midlands within a commercial timber plantation and a neighbouring protected area (PA). Flower-visitor observations were carried out in uninvaded protected areas and RGPs and in protected areas and RGPs invaded by R. cuneifolius. I found that RGPs within commercial forestry plantations successfully decrease the negative effects of land transformation on the grasslands of the KwaZulu-Natal Midlands, and flower visitation network patterns are largely maintained in these habitat fragments. However, within RGPs, invasion by R. cuneifolius affected the composition and the interaction network structure of flower-visitor and plant communities. The fact that there are unplanted areas within commercial forestry plantations is positive for biodiversity conservation in South Africa. Research has indicated that these areas successfully aid in the conservation of biodiversity and ecosystem functioning. Due to the positive influence that RGPs have on conservation in fragmented and transformed landscapes, it is critical that these unplanted areas are retained. However, the effects of bramble invasion are more intense within RGPs than within protected areas, and therefore, it must be a priority to keep these areas undisturbed. R. cuneifolius has been found to have devastating effects on ecosystem function and network structure. It is also a category 1 invasive plant within South Africa, and its removal is required by law. Therefore, the removal of bramble must be a management priority. | AFRIKAANSE OPSOMMING: Ons planeet is in die middel van 'n biodiversiteit krisis, met faktore soos grond transformasie, klimaatsverandering, antropomorfiese versteuring en indringerspesies wat gesamentlik werk om biodiversiteit te bedreig. Suid-Afrika, besit minimale houtbronne. Daarom is kommersiële bosbou een van die mees algemene vorme van landskap transformasie. Tog is 'n derde van die land binne baie plantasies opsy gesit vir bewaring as oorblywende grasveld kolle (OGKs). Hierdie gebiede word ongelukkig blootgestel aan die bykomende negatiewe impak van die uitheemse spesies, Rubus cuneifolius (Amerikaanse steekdoring), wat veral problematies is in en rondom bosbouplantasies. Die grasveldbioom van Suid-Afrika is baie divers en is van kardinale belang vir die ekosisteem dienste wat dit lewer. Ten spyte hiervan, word die grasveldbioom bedreig waar dit op dieselfde areas as die meerderheid van Suid-Afrika se bosbouplantasies geleë is. Antropomorfiese versteuring lui daartoe dat bestuiwergetalle daal. Landskap transformasie vir bosbou plantasies raak dus plant-bestuiwer interaksies, wat ekosisteme en biodiversiteit beïnvloed. Dit is nie bekend tot watter mate hierdie ekosisteme geraak word nie. Daar word vermoed dat die impak af hang van die kompleksiteit van die ekosisteem. Ontledings van ekosisteme op netwerk vlak kan insigte bied oor die robuustheid van hierdie ekosisteme in die aangesig van biodiversiteitverlies. Dus, die studie evalueer die effek van fragmentasie van natuurlike habitatte en inval van die indringer spesie, R. cuneifolius, op blom-besoekings netwerke van Suid-Afrikaanse grasvelde. Hierdie studie is uitgevoer in die KwaZulu-Natal Midlands binne 'n kommersiële hout plantasie en 'n naburige beskermde gebied (BG). Blom-besoeker waarnemings was in BGs en OGKs sonder R. cuneifolius, en in BGs en OGKs met R. cuneifolius uitgevoer. Ek het gevind dat OGKs binne kommersiële bosbouplantasies suksesvol is om die negatiewe uitwerking van land transformasie te verminder, en blom-besoeking netwerk patrone grootliks gehandhaaf word in hierdie habitat fragmente. Egter, binne OGKs, het R. cuneifolius die samestelling en die interaksie netwerk struktuur van blom-besoekers en plant gemeenskappe negatief geraak. Die feit dat OGKs ongeplant gelaat word, is positief vir die bewaring van biodiversiteit in Suid- Afrika. Navorsing dui aan dat hierdie gebiede suksesvol is om te help met die bewaring van biodiversiteit en ekosisteemfunksionering. As gevolg van die positiewe invloed van OGKs op bewaring in gefragmenteerde en omskepte landskappe, is dit krities dat hierdie areas ongeplant bly. Egter, die gevolge van steekdoring inval is meer intens binne OGKs as binne beskermde gebiede, en daarom moet dit 'n prioriteit wees om hierdie gebiede ongestoord te hou. R. cuneifolius se verwoestende uitwerking op ekosisteem funksie en netwerk struktuur was baie duidelik. Dit is ook 'n kategorie 1 indringerplant in Suid-Afrika, en sy verwydering word deur is die wet vereis. Daarom moet die verwydering van steekdoring ‘n bestuursprioriteit wees.