UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Ocean and Earth Sciences Species compensatory responses and biodiversity- ecosystem function relations by Matthias Schmidt Thomsen Thesis for the degree of Doctor of Philosophy May 2018 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES Ocean and Earth Sciences Thesis for the degree of Doctor of Philosophy Species compensatory responses and biodiversity-ecosystem function relations Matthias Schmidt Thomsen Anthropogenic activities affect ecosystems and alter community dynamics and species interactions, which can have with significant consequences for biodiversity- function relations. Current knowledge on the role of biodiversity in mediating ecosystem processes and functions is largely derived from controlled, biodiversity manipulation experiments. However, these studies rarely account for species compensatory responses that potentially represent an important ecological response to perturbations in natural systems. Incorporating species compensation into empirical studies or predictive models has the potential to fundamentally change perceptions of the ecosystem consequences associated with changing biodiversity, but has received little attention. Here, I explicitly incorporate aspects of biodiversity change that have not previously been included within the biodiversity-ecosystem function framework. By adopting a range of approaches, including trait-based models, laboratory-based mesocosm experiments and field observations, I explore the role of compensation in marine benthic communities. Results show that scenarios of species loss that include community compensatory responses are fundamentally different to those where response mechanisms are excluded. However, the ecosystem consequences of compensation depend on the type and expression of compensation. I demonstrate that the functional traits of the species driving the compensatory response, and their relative abundance within the community, is highly important in determining the functional outcome of altered biodiversity. Although, a consistent feature across communities, irrespective of the driver of perturbation, the functional consequences of compensatory responses are also dependent on environmental context. The general paradigm that emerges is that compensatory responses exist in natural systems and are likely to alter the form of biodiversity-function relations, leading to changes in ecosystem properties that differ from current expectation. I conclude that, in order to project the ecosystem consequences of anticipated levels of biodiversity change, it will be necessary to acknowledge the role of compensation in natural systems to ensure the benefits that ecosystems provide society are sustained. Table of Contents Table of Contents ..................................................................................................................... i List of Tables ............................................................................................................................. v List of Figures ........................................................................................................................ vii Academic Thesis: Declaration of Authorship ........................................................ xi Acknowledgements ............................................................................................................ xiii Chapter 1: General Introduction ..................................................................................... 1 1.1 Introduction ..................................................................................2 1.2 Thesis aims and objectives .......................................................... 10 Chapter 2: Consequences of biodiversity loss diverge from expectation due to post-extinction compensatory responses ..................... 13 2.1 Abstract ...................................................................................... 14 2.2 Introduction ................................................................................ 14 2.3 Methods ...................................................................................... 16 2.3.1 Sampling and study site ........................................................ 16 2.3.2 Extinction simulations ........................................................... 16 2.3.3 Compensation by common species ....................................... 17 2.3.4 Compensation by rare species ............................................... 17 2.3.5 Compensation by species from within/outwith or lower/higher functional grouping or which exhibit similar/distinct or lower/higher levels of activity ........................................... 18 2.4 Results ........................................................................................ 18 2.5 Discussion ................................................................................... 23 2.6 Acknowledgements ..................................................................... 25 Chapter 3: Compensatory responses can modify the form of the biodiversity-function relation curve contingent on post- extinction community composition .................................................. 27 3.1 Abstract ...................................................................................... 28 3.2 Introduction ................................................................................ 28 3.3 Methods ...................................................................................... 30 i 3.3.1 Faunal and sediment collection ............................................. 30 3.3.2 Experimental design ............................................................. 31 3.3.3 Measurements of ecosystem process and functioning ........... 32 3.3.4 Statistical analyses ............................................................... 32 3.4 Results ....................................................................................... 33 3.4.1 Effects on particle reworking and burrow ventilation ............. 33 3.4.2 Effects on nutrient generation .............................................. 37 3.5 Discussion .................................................................................. 39 3.6 Acknowledgements ..................................................................... 42 Chapter 4: Capacity of benthic communities in sustaining ecosystem functioning depends on the intensity of anthropogenic forcing ................................................................................................................ 43 4.1 Abstract ...................................................................................... 44 4.2 Introduction ................................................................................ 44 4.3 Methods ..................................................................................... 47 4.3.1 Area of study ....................................................................... 47 4.3.2 Sample collection ................................................................. 47 4.3.3 Approach, analysis and data ................................................. 49 4.3.4 BQPc ..................................................................................... 51 4.3.5 Species evenness J’ ............................................................... 52 4.4 Results ....................................................................................... 52 4.5 Discussion .................................................................................. 60 4.6 Acknowledgements ..................................................................... 63 Chapter 5: Environmental perturbation destabilises benthic community structure and dynamics ............................................................................ 65 5.1 Abstract ...................................................................................... 66 5.2 Introduction ................................................................................ 66 5.3 Methods ..................................................................................... 68 5.4 Results ....................................................................................... 70 5.5 Discussion .................................................................................. 77 5.6 Acknowledgements ..................................................................... 79 ii Chapter 6: General Discussion ..................................................................................... 81 6.1 Summary of main conclusions and recommendations ................... 88 Appendices .............................................................................................................................. 93 Appendix A ............................................................................................................................... 95 Appendix B ............................................................................................................................ 100 Appendix C ............................................................................................................................ 124 Appendix D ........................................................................................................................... 133 Appendix F ............................................................................................................................ 156 List of References ............................................................................................................