Biodiversity and Ecosystem Processes In the Strandline: The Role of Species ]dentit>', Diversity, Interactions and Body Size By Sally Jane Marsh A thesis submitted to the University of Plymouth in partial fulfillment for the degree of DOCTOR OF PHILOSOPHY School of Biological Sciences, Faculty of Science In collaboration with Plymouth Marine Laboratory January 2008 University of Plymouth Library Shelfma,-1< Biodiversity' and Ecosystem Processes in the Strandline: The Role of Species ldentit>', Diversity, Interactions and Body Size Sally Jane Marsh Abstract In ihe current climate of biodiversity loss how species diversity and ecosystem process are linked is, arguably, one of the most pressing issues and greaiesl challenges currently facing the scientific community. Previous studies suggest that there is no universal Irajcciory for the relationship between diversity and ecosystem processes, the pattern depends largely on species identity and their interactions. Furthermore, the effect of reduced diversity on ecosystem process in multi-trophic assemblages is both understudied and poorly understood. Consequently, the overall aim of the present study was to investigate the role of species identity, diversity and interactions in determining ecosystem processes using the strandline as a model system. Appropriate strandline species, three species of kelp fly larvae, an amphipod and four rove beetles were were selected for use in laboratory manipulative experiments that measured decomposition as an ecosystem process. This study is one of the few to consider the affect of species interactions on ecosystem processes. The use of metabolic theory to make predictions of trophic interactions and ecosystem processes, using tractable surrogate measures of interaction strength, was also investigated. Finally, the importance of trophic interactions in affecting ihe connection between ecosystem processes and consumer species identity, diversity and interactions was examined. Species identity combination explained the variability in decomposition when strandlinc decomposer diversity and identity were manipulated. Positive and negative interactions were identified, and the effect of diversity on decomposition was dependent on the balance of these negative and positive species interactions. A mechanism of microbial facilitation and inhibition was proposed to explain the outcome as no previously proposed single mechanism adequately described the observed effect of species identity, diversity and interactions on ecosystem process found in this study. It was not possible to accurately predict obser\'cd predator-prey interaction strengths and ecosystem processes between strandline predators and prey and decomposition using body size as a surrogate measure of interaction strength and ecosystem processes. Although body size was an important factor explaining the variability in predator-prey interactions and decomposition, so too was species identity. The absence of a consistent relationship between size and interaction strength and decomposition was attributed to species-specific differences. The presence of trophic interactions subtly affected decomposition of wrack by strandline delrilivores. However, in the presence and absence of a predator the overall effect of detritivore diversity and interactions on decomposition remained constant. The results of this study have implications for the fields of biodiversity ecology, metabolic theory of ecology and food web ecology. Firstly, the identification of positive detritivore-resource interactions adds to a growing body of evidence that some detrilivore species may interact positively, with respect to ecosystem processes. The loss of species within a trophic group may result in a greater reduction in ecosystem processes than previously thought. If positive species interactions are prevalent, ecosystem process will decrease to a greater extent as species are lost, than that predicted from single species processing rates. By considering species interactions, future biodiversity ecosystem processing studies may better understand the effects of species diversity and identity on ecosystem process. It is also suggested that patterns and relationships uncovered in previous studies investigating the effects of species from a single trophic level on ecosystem process may still be valid in more realistic multi-trophic systems. If future biodiversity-ecosystem process studies are to make predictions concenning actual species-ecosystem process interactions in real assemblages the size of constituent species should be considered, as predator and prey size was shown to effect predator-prey interactions and ecosystem processes. The results of this study also suggest that allometry and metabolic theory have limited capacity for making predictions of predator-prey interactions and ecosystem processes, at least at the scale investigated here. Species specific factors are more likely to explain the patterns of predator-prey interactions and ecosystem processes at smaller scales. Unless food web models consider, or allocate, non-trophic interactions correctly, erroneous predictions of energy How and ecosystem process may result. Finally, the use of body size and allomelric scaling laws to quantify food web models and energy fiow through an assemblage must be treated with caution if these models are used to make predictions on interactions between species and ecosystem processes occurring at the scale investigated in this study. Acknowledgments I would like lo thank NERC for providing the fianding for this PhD and providing me with this excellent opportunity. Many thanks to all my supervisors for their support and help. I would especially like to thank John Spicer whose constant help, enthusiasm and good humour made this PhD both possible and a fantastic learning experience. I would also like to thank Dave Bilton for his help with beetle identification and invaluable advice regarding their natural history. Also Dave Raffaelii for his enthusiasm and help with the theoretical aspects of this project and for introducing me to Guy Woodward, Jose Montoya, Mark Emmerson and Phil Warren, whose comments on this project's rationale were much appreciated, i also express my gratitude to Bob Clarke and Andy Foggo for allowing me to pick their brains on statistical matters throughout this work. Thank you to Ann Torr, Pete Smithers, Roger Haslam, Alex, Joolz and Richard Ticehurst who helped enormously with the practical aspects of this project and also allowed me to fill the 6* floor, 7'^ floor and S**" floor labs with rotten wrack, larvae, beetles and amphipods. I wish to thank all the students that helped with the field and lab work, Elizabeth McAfee, Zoe Hutchinson, Saskya Richardson, with special thanks to Rachel Bott for all her help with chapter 3 and Rob Ellis who helped set up many experiments at unsociable hours and even cycled to Wembury to help collect samples. 1 also wish to thank the whole of MBERC, who were amazing to work with and made this PhD experience all the more fun. Thank you to everyone who helped out either in the field the lab or provided brain support. I would particularly like to thank Pip Moore, Sophie Mowles, Marta Soffker, John Griffin, Awantha Dissanayake and Martin Canty for their comments on various chapters in this thesis. I must also thank; Richard Hartley, Mark Browne, Emma Jackson, Sam Glanfield, Pete Cotton, Simon Rundle, Kalh Sloman and Emma Sheehan. Last but far from least I would particularly like to thank my friends and family for their patience, understanding and moral support. Author's Declaration At no time during the registration for degree of Doctor of Philosophy has the author been registered for any other University award. This study was funded by the Natural Environment Research Council. Presentations and Conferences Attended. S. Marsh, J.I. Spicer, S. Widdicombe (2007) Biodiversity and Ecosystem Processes in the strandHne. Oral Presentation. Change in aquatic ecosystems. Conference 2-6^^ July 2007, Plymouth. S. Marsh, J.l. Spicer, S.Widdicombe, A. Rees and J. Blackford (2005) Biodiversity and Ecosystem Function: Can Body Size and Food Webs be used to Elucidate the Relationship (2005). Poster Presentation. The British Ecological Society Special Symposium. Body Size and the Organisation of Aquatic Ecosystems. 2-4 September 2005. de Havilland Campus, University of Hertfordshire, Hatfield, Herts, ALIO 9EU, UK. S. Marsh, J.i. Spicer, S.Widdicombe, A. Rees and J. Blackford (2005)Measuring, Mapping and Modelling Denitrification and Bioturbation. Poster Presentation. The First Nereis Park conference November 7-9, 2004,Carry-Le-Rouet, Bouches-du-Rhone, France. Worshops and Courses Attended. PRIMER 6.2 Workshop. (2006) Five-day course. Instructors Bob Clarke, Richard Warwick and Paul Somerfield. The Marine Biological Association of the UK, Citadel Hill, Plymouth. Undertaking a Systematic Review Workshop (2007) One- Day course taught by Gavin Steward, funded by the Society for Conservation Biology. 28, 2007. University of Birmingham. QUEST Earth Systems Science Summer School (ES4 4) (2004) 10-day course run by Prof Brian Hoskins (Reading) and Prof Peter Liss (East Anglia). 13-24 September 2004. Department of Meteorology, University of Reading. Signed...>^<^^.., \\\ Table of Contents Abstract i Acknowledgments ii Author's Declaration iii CHAPTER 1: INTRODUCTION I 1.1 Chapter Aims and Outline 1 1.2 Biodiversily and Ecosystem Function - Definitions and Importance 2 1.3 A Brief Introduction to Biodiversity