Diversity and resource choice of flower-visiting insects in relation to pollen nutritional quality and land use Diversität und Ressourcennutzung Blüten besuchender Insekten in Abhängigkeit von Pollenqualität und Landnutzung Vom Fachbereich Biologie der Technischen Universität Darmstadt zur Erlangung des akademischen Grades eines Doctor rerum naturalium genehmigte Dissertation von Dipl. Biologin Christiane Natalie Weiner aus Köln Berichterstatter (1. Referent): Prof. Dr. Nico Blüthgen Mitberichterstatter (2. Referent): Prof. Dr. Andreas Jürgens Tag der Einreichung: 26.02.2016 Tag der mündlichen Prüfung: 29.04.2016 Darmstadt 2016 D17 2 Ehrenwörtliche Erklärung Ich erkläre hiermit ehrenwörtlich, dass ich die vorliegende Arbeit entsprechend den Regeln guter wissenschaftlicher Praxis selbständig und ohne unzulässige Hilfe Dritter angefertigt habe. Sämtliche aus fremden Quellen direkt oder indirekt übernommene Gedanken sowie sämtliche von Anderen direkt oder indirekt übernommene Daten, Techniken und Materialien sind als solche kenntlich gemacht. Die Arbeit wurde bisher keiner anderen Hochschule zu Prüfungszwecken eingereicht. Osterholz-Scharmbeck, den 24.02.2016 3 4 My doctoral thesis is based on the following manuscripts: Weiner, C.N., Werner, M., Linsenmair, K.-E., Blüthgen, N. (2011): Land-use intensity in grasslands: changes in biodiversity, species composition and specialization in flower-visitor networks. Basic and Applied Ecology 12 (4), 292-299. Weiner, C.N., Werner, M., Linsenmair, K.-E., Blüthgen, N. (2014): Land-use impacts on plant-pollinator networks: interaction strength and specialization predict pollinator declines. Ecology 95, 466–474. Weiner, C.N., Werner, M , Blüthgen, N. (in prep.): Land-use intensification triggers diversity loss in pollination networks: Regional distinctions between three different German bioregions Weiner, C.N., Hilpert, A., Werner, M., Linsenmair, K.-E., Blüthgen, N. (2010): Pollen amino acids and flower specialization in solitary bees. Apidologie 41 (4), 476-487. 5 6 Pantoum on Nature's Patience (by Mark R Slaughter) Surviving all to seize the hour; A firm reward: a solitary flower. With pinch of time to propagate - Of seed and chance, it must await. A firm reward: a solitary flower, But motionless, the dainty tower. Of seed and chance, it must await And not by dreams or wishing fate. But motionless, the dainty tower - Completion lies in gusty power, And not by dreams or wishing fate. Unmindful patience; whither date? […] Pulsatilla vulgaris © Christiane N. Weiner 7 8 Inhaltsverzeichnis Summary _________________________________________________________________ 11 Zusammenfassung __________________________________________________________ 15 1. General introduction _____________________________________________________ 19 1.1 Why study biodiversity and ecosystem functions? __________________________________ 19 1.2 Facts and considerations about mutualistic plant-flower visitor interactions _____________ 21 1.3 The Biodiversity Exploratories _________________________________________________ 30 1.4 Thesis outline ______________________________________________________________ 31 2. Effects of meadow management on diversity, composition and specialization of plant- flower visitor interactions ____________________________________________________ 33 2.1 Introduction _______________________________________________________________ 34 2.2 Methods __________________________________________________________________ 35 2.3 Results ____________________________________________________________________ 39 2.4 Discussion _________________________________________________________________ 43 3. Mutualistic networks and their response to disturbance in relation to diversity and specialization _____________________________________________________________ 47 3.1 Introduction _______________________________________________________________ 47 3.2 Methods __________________________________________________________________ 49 3.3 Results ____________________________________________________________________ 55 3.4 Discussion _________________________________________________________________ 59 4. Differences in land-use effects on plant-pollinator interaction across three different German bioregions _________________________________________________________ 87 4.1 Introduction _______________________________________________________________ 87 4.2 Methods __________________________________________________________________ 89 4.3 Results ____________________________________________________________________ 94 4.4 Discussion ________________________________________________________________ 110 5. Pollen amino acids and flower specialization in solitary bees ____________________ 121 5.1 Introduction ______________________________________________________________ 121 5.2 Methods _________________________________________________________________ 123 5.3 Results ___________________________________________________________________ 126 5.4 Discussion ________________________________________________________________ 134 6. Diversity and resource choice of flower visiting insects in relation to pollen nutritional quality and land use – synopsis and discussion _________________________________ 137 6.1 Land-use effects on plant communities _________________________________________ 137 6.2 Consequences from land use for mutualistic plant-pollinator interactions ______________ 139 6.3 Pollen nutritional quality in relation to specialization in pollinators ___________________ 143 9 6.4 Conclusions _______________________________________________________________ 144 Literature _______________________________________________________________ 145 Acknowlegements _________________________________________________________ 159 Curriculum Vitae _________________________________________________________ 161 Author contributions ______________________________________________________ 163 List of publications ________________________________________________________ 164 10 Summary Recent declines in honey bee colonies as well as in the diversity and abundance of native pollinators generated widespread concern about the future of pollination and set off a discussion about a general “pollination crisis”. Partly, this is due to the functional importance of this ecosystem service not only for plant reproduction but above all for crop production and thus human welfare. Consequently, the matter gained particular attention in current research and a rising number of studies focus on the stability of plant-pollinator interactions in relation to biodiversity and ecosystem change. My dissertation focuses on the mutualistic interactions between flowering plants and flower-visiting insects and their interactive response to land-use intensity as well as resource choice of flower-visitors in relation to pollen quality. The innovative approach of my project is to use quantitative interaction networks to provide knowledge on how species respond to land use and how their responses may influence their interaction partners. We show that information from ecological networks may help to predict natural community responses to disturbance and possible secondary extinctions in systems that undergo agricultural intensification, if the identity of each species’ partners and relative interaction strengths are considered. This project presents large-scale investigations on the characteristics and fragility of multi-species networks in real landscapes. During two seasons we recorded the diversity, species composition and specialization of plant-pollinator networks along a gradient of increasing land-use intensity. The study was conducted within the framework of the Biodiversity Exploratories, which are located in the Schorfheide-Chorin (NE Germany), Hainich- Dün (Central Germany) and Schwäbische Alb (SW Germany) regions. Each Exploratory contains 50 experimental grassland plots which comprise near natural, protected sites as well as intensively fertilized, mown or grazed meadows and pastures. Comparing meadows of high and low land-use intensities we found that species richness of plants, bees and butterflies was significantly higher on low intensity meadows. However, in terms of Shannon diversity and abundance only butterflies 11 responded negatively to land-use intensification (Chapter 2). Nevertheless, the analysis of plant and flower-visitor composition revealed crucial differences between grassland types with species overlaps of just 43 % in plants and 42 % in insects. This pointed to the fact that investigation of biodiversity and abundance alone may not detect biotic homogenization e.g. a loss in functional diversity. Moreover, resource impoverishment had stronger effects on the land-use response of highly specialized flower-visitor groups than on little or unspecialized ones. We examined if mutual specialization could explain the accelerating parallel declines observed in plants and pollinators. Focusing on their stability, we analyzed 162 plant- pollinator networks from 119 meadows and pastures managed at different intensities. The fate of a flower visitor was predicted by the land-use response of its associated plant species and vice versa. Furthermore, we detected a disproportional impact of land- use intensification on the abundance of more specialized pollinator species (Chapter 3). Land-use intensification seems to set off losses in flower diversity, which leads to resource-mediated declines in pollinator species. While the mean land-use response of the pollinators visiting