Niche and neutral processes in a dry grassland: the example of oribatid mites Inaugural-Dissertation to obtain the academic degree Doctor rerum naturalium (Dr. rer. nat.) submitted to the Department of Biology, Chemistry and Pharmacy of Freie Universität Berlin by Stefanie Maaß born in Berlin 2015 This work was carried out between 2012 and 2015 under the supervision of Prof. Dr. Matthias C. Rillig, Institut für Biologie, Freie Universität Berlin, Germany. Supervisor: Prof. Dr. Matthias C. Rillig Co-Supervisor: Dr. Tancredi Caruso 1st reviewer: Prof. Dr. Matthias C. Rillig Institut für Biologie, Freie Universität Berlin, Germany. 2nd reviewer: Prof. Dr. Mark Maraun J.-F.-Blumenbach-Institut für Zoologie und Anthropologie, Georg-August-Universität Göttingen, Germany. Date of disputation: 21st September 2015 The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka! (I found it!)' but 'That's funny...' Isaac Asimov Copyright by STEFANIE MAAß Berlin 2015 Acknowledgement Thanks to Prof. M.C. Rillig for supervising this thesis and giving me the chance to work on this topic. I also would like to thank Prof. M. Maraun for being second reviewer. Additionally, thanks for the very interesting discussions about the peculiarities of oribatid mites and stable isotope analysis. Special thanks to the Friedrich-Naumann-Stiftung für die Freiheit for financial and also educational support. This is for Dr. T. Caruso: Vi ringrazio di tutto! Thanks for giving me the opportunity learning from you and scientifically growing up. Thanks for your patience! The Italian-Prussian cooperation worked very well and I hope will continue to do so in the future! Of course, the whole lab deserves many thanks for the great time! Thanks for giving me advise although my topic has been quite different from yours. Special thanks to Anika Lehmann for cheering me up several times and always patiently answering my questions. Thanks to my family and their loving endless support in every respect! Special thanks to my dearly beloved husband for his endless love, optimism, patience and support! Foreword This dissertation is a cumulative work of the following published manuscripts. The bibliographic references cited through all chapters are listed together after Chapter 8. I Maaß, S., Maraun, M., Scheu, S. Rillig, M.C., Caruso, T. 2015. Environmental filtering vs. resource-based niche partitioning in diverse soil animal assemblages. Soil Biology and Biochemistry 85: 145-152. http://dx.doi.org/10.1016/j.soilbio.2015.03.005. II Maaß, S., Caruso, T., Rillig, M.C. 2015. Functional role of microarthropods in soil aggregation. Pedobiologia 58: 59-63. http://dx.doi.org/10.1016/j.pedobi.2015.03.001. III Maaß, S., Migliorini, M., Rillig, M.C., Caruso, T. 2014. Disturbance, neutral theory and patterns of beta diversity in soil communities. Ecology and Evolution 4:4766- 4774. http://dx.doi.org/10.1002/ece3.1313. Contents 1 General Introduction ................................................................................................................... 3 2 Environmental filtering vs. resource-based niche partitioning in diverse soil animal assemblages .............................................................................................................................. 15 3 Functional role of microarthropods in soil aggregation ........................................................... 29 4 Disturbance, neutral theory and patterns of beta diversity in soil communities: the example of oribatid mites ............................................................................................................................ 36 5 General Discussion ................................................................................................................... 47 6 Summary ................................................................................................................................... 56 7 Zusammenfassung .................................................................................................................... 58 8 References ................................................................................................................................ 60 9 Contribution to chapters ........................................................................................................... 89 10 Appendix .................................................................................................................................. 90 Appendix A. Information about soil oribatid mite community ........................................ 91 Appendix B. Supplementary information for Chapter 2 .................................................. 93 Appendix C. Supplementary information for Chapter 4 ................................................ 100 Appendix D. Supplementary Data for discussion: Co-occurrence analysis ................... 113 Appendix E. List of figures ............................................................................................ 123 Appendix F. List of tables .............................................................................................. 124 1 General Introduction The huge biodiversity on Earth has fascinated generations of scientists (Morin 2011)and has received more and more attention, unfortunately mostly in terms of increasing biodiversity loss due to habitat loss or environmental pollution. But also the basic mechanisms of how biodiversity is maintained in the respective habitats have been studied intensely. In this work, we aim at studying a group of organisms, namely oribatid mites, to unravel potential mechanisms behind coexistence which results in an amazingly high diversity in a seemingly homogeneous environment like soil. We therefore try to use different theoretical approaches from niche and neutral frameworks which have had a strong impact on ecological research during the last century. Theoretical background Before the 18th century, the work of biologists has been rather unordered and natural phenomena were explained rather mystically than scientifically. More descriptive approaches had not started before the 18thcentury and the Church had still a lot of influence on the people‟s perception of the world. The work of e.g. Carl Linnaeus (1707-1778) who developed the scientific nomenclature, was the starting point for ordered scientific research. He already used definitions and descriptions to highlight the differences among species which can be interpreted as an early attempt of developing concepts of biodiversity and the ecological niche as we know it today (Chase & Leibold 2003). Additionally, in the 1750s, Georges-Louis Leclerc Count de Buffon (1707- 1788) described that despite of having similar environments, regions differ in their species compositions (later known as Buffon‟s Law), which is nowadays considered to be the first principle of biogeography. In the 19th century, two names are especially connected to the scientific advances in ecology in Europe: Alexander von Humboldt (1769-1859) and Charles Darwin (1809-1882), the former also laying the foundation for biogeography with his works especially on botanical geography, and the latter with his revolutionizing work on natural selection which is still valid today. But also Alfred Russel Wallace (1823-1913), at the same time, discovered the mechanism of natural selection („Ternate manuscript‟ from 1858). Darwin‟s works on evolution and natural selection can be interpreted as description of the species‟ niche, however, he used the wording „line of life‟ to describe the unique role of a species (Chase & Leibold 2003). In 1877, Karl Möbius (1876-1953) was the first to describe the interaction of different organisms and coined the term „biocenose‟ which is also still in use today. Adding to this, in 1896, the Danish botanist Johannes Eugenius Bülow Warming (1841-1924) was the first to officially ask the basic, seemingly trivial but still unanswered questions of ecology: „Why does each species has its own habitat? How do species congregate to form characteristic communities?„ (Warming 1895). 3 20th century In 1913, the British Ecological Society was founded with Arthur Tansley (1871-1955), who was influenced by Warming, being its first president (www. britishecologicalsociety.org). The Society aimed at „promoting and foster the study of Ecology in its widest sense‟. Shortly after, in 1915, Victor Ernest Shelford (1877-1968) was involved to found the Ecological Society of America and became its president in 1916 (www.esa.org). These two events marked the beginning of „ecology‟ as a distinct field in science. Another influential theory is Frederic Edward Clements‟s (1874-1945) climax theory of vegetation (1936) which suggests that after a disturbance the vegetation comes back to a „climax state„ which consists of the vegetation composition best adapted to the local conditions. In contrast to that, in 1917, Henry Allan Gleason (1882-1975) published an „individualistic concept of ecology‟ where „the phenomena of vegetation depend completely upon the phenomena of the individual species‟ and argued that the distribution of plants follows more randomness rather than being deterministically structured. This approach did not gain popularity until the 1950s, but since then „species- individualistic‟ models have become very important in ecology (McIntosh 1995). However, the idea of the niche was already established by Joseph Grinnell (1877–1939), whose name is also strongly connected to the development of niche