Nom/Logotip de la Universitat on s’ha llegit la tesi Understanding constraints and potentials of weed management through seed predation by harvester ants Atanackovic Valentina Dipòsit Legal: L.705-2013 http://hdl.handle.net/10803/112029 ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. 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Understanding constraints and potentials of weed management through seed predation by harvester ants PhD student Valentina Atanackovic 2 Understanding constraints and potentials of weed management through seed predation by harvester ants DISSERTATION To obtain the degree of Doctor by the University of Lleida MEMÒRIA DE TESI Per optar al grau de Doctor per la Universitat de Lleida By Per Valentina Atanackovic 2013 Departament d’Hortofructicultura, Botànica i Jardineria Escola Tècnica Superior d’Enginyeria Agrària Universitat de Lleida 3 4 Supervisors Dr Paula R. Westerman (Rostock Universität, Germany) Dr Joel Torra (Agrotecnio, Universitat de Lleida, Spain) External evaluators: Dr Cesar Fernandez-Quintanilla (CSIC Madrid, Spain) Dr Francisco M. Azcarate (Universidad Autónoma de Madrid, Spain) Comitee members: Dr Cesar Fernandez-Quintanilla (CSIC Madrid, Spain) Dr Alicia Cirujeda (CITA Aragón, Spain) Dr Xavier Pons (Universitat de Lleida, Spain) Substitutes: Dr Carlos Cantero (Universitat de Lleida, Spain) Dr Xavier Sans (Universitat de Barcelona, Spain) 5 6 Acknowledgements During my work on PhD thesis, some people did help and support me with their presence, kind advice and suggestions that facilitated my work and allowed me to make progress. I wish to thank all of them saying few words to remind them how important they were to me. From the beginning, Dr Paula Renate Westerman and the first e-mails before I came to Spain. Thanks to her understanding and effort, I left my small lab in the Botanical Garden in Belgrade and then I got the opportunity to open the new wonderful door of the area of SEED PREDATION. I wish to thank her for the guidance of the thesis and the availability at any time from any place in the world (Spain, Netherlands, USA, Germany, etc.). I think that her many corrections and critiques enabled me to cope with the obstacles. This thesis would not have been provided in its present form without her supervision. I am, also, grateful to Dr Joel Torra who was my second supervisor, for being enthusiastic in helping me from the early days in Spain up until the last corrections in the manuscript. I wish to thank him for being there in the great, and in the difficult moments during the work. Many thanks to Paula and Joel! I wish to thank to my tutor Dr Aritz Royo-Esnal for the support and wonderful friendship. He taught me Spanish at the beginning and helped in any moment. I, also, want to thank Dr Jose Manuel Blanco Moreno for his great help in the fifth chapter that improved a quality of the thesis. I want to thank Dr Jordi Recasens for the financial support and understanding during these years. My field work during hot Spanish summers was made easier and more pleasant thanks to the best technicians in the world, Nuria Moix and Sergi Royan. Thank you, guys! I appreciate the department of Hortofructicultura, Botànica i Jardineria, especially Dr Josep Antoni Conesa and always kindly Nuria Llop. I am expressing my gratitude to the department of Crop Health at University of Rostok for their hospitality and kindness. I thank wholeheartedly to my Chilean friend, Robert Fuentalba Ojeda, for helping me resolving doubts and sharing his extensive field experience considering the hidden aspects of the life of ants. 7 I wish to thank to the kind farmers Xavi Llobet and Joan Ribes for allowing the experiments to take place on their fields during my PhD work. To my friends Barbara, Addy Laura, Xavi, Alex and Irene I thank for being together with me and, sharing our daily life. I did spend nice time with them. The last but not the least I wish to thank to my husband and my parents who trusted in me, supported me and accepted the inconveniences of the situation. Finally, it was not easy to have a mother that was always busy with her PhD work, but, my daughter, Alisa, always stayed by my side, although she had to learn completely new languages and move to the new country. She made my days brimming trough her love. 8 This research was developed in the group of Malherbología y Ecología Vegetal of the Universitat de Lleida. The author was funded by a PhD grant of Universitat de Lleida. Part of the research was done in Germany (Group of Crop Health, Rostock Universität), and was supported by Ministry of Education and Science of Spain (projects AGL 2007- 60828 and AGL 2010-22084-C02-01). 9 10 To my daughter Alisa 11 12 Contents Summary 15 Resumen 18 Resum 22 Chapter 1 General Introduction 25 Chapter 2 Differential weed seed removal in dryland cereals 39 Chapter 3 Density independent weed seed removal by 65 harvester ants in dryland cereals Chapter 4 Effect of weed patch size on seed removal by harvester ants 87 Chapter 5 The spatial distribution of nests of harvester ants 109 (Messor barbarus L) in dryland cereals Chapter 6 General discussion 139 Conclusions 149 Conclusiones 151 Conclusions (català) 153 13 14 Summary In dryland fields in NE Spain, the harvester ant M. barbarus is the main seed predator. Post-dispersal seed predation by harvester ants is high (78%) in spring and summer. One characteristic of seed predation is that it is variable over time and space. This variability can influence the efficacy of granivory and may provide opportunities to weeds to escape predation. However, factors that determine the temporal and spatial variability in predation rates are largely unknown. This knowledge could help to better understand the constraints and potentials of seed predation by harvester ants for weed management. Seed predation rates by harvester ants in dryland cereals were among the highest ever recorded on arable fields (46-100%). The reason for the high rates is that the timing of weed seed shed overlapped with the period of highest demand. However, a small proportion of newly shed seeds were not consumed because of crop harvest or low preference. Some seeds escaped predation due the small size that allowed fast seed burial. Of the seeds of Bromus diandrus about 15 to 25% avoided predation because of low preference to ants, while 0–29% escaped through crop harvest. Of the seeds of Papaver rhoeas, 20–32% escaped through crop harvest, while another 13–17% escaped by fast burial into the soil. It is clear that both would cause more problems in arable fields without the presence of seed predators. The spatial distribution of ant nests was investigated because it could influence seed predation rates due to unequal foraging intensities within a field. The spatial nest arrangement appeared to be non-random. The large nests were more or less regularly distributed, but small nests tended to be more clumped.