Controls on the distribution of specialist invertebrates inhabiting exposed riverine sediments in England and Wales Matthew John O’Callaghan A thesis submitted to the University of Birmingham for the degree of Doctor of Philosophy School of Geography, Earth and Environmental Sciences College of Life and Environmental Sciences University of Birmingham June 2011 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Occupying a disjointed and vulnerable habitat, specialist Coleoptera associated with Exposed Riverine Sediments (ERS) are shown to exhibit high levels of adaptation. An assessment of the English and Welsh habitat resource confirms the presence of strong geographical and physical restraints on its distribution which partially explain the rarity of some of the associated Coleoptera. Assemblage studies reveal the presence of multiple adaptive strategies that enable specialists to utilise the resource in spite of perceived environmental pressures, and the strength of these morphological and behavioural adaptations can be used to predict abundance and distribution at alpha, beta and gamma levels. Furthermore, adaptations enforce varying nutrient acquisition strategies which spatially define communities. This study demonstrates the need specialist invertebrates have for a complex and highly connected ERS habitat with English and Welsh rivers, that exhibits structural variation along a longitudinal gradient. Reliant on riverine processes and subsidies the habitat and its associated invertebrates are symptomatic of a healthy and naturally structured lotic system operating laterally and across reach scales. Acknowledgements The support, advice and guidance of the following people have been invaluable in the completion of this research: my supervisors Jon Sadler, David Hannah and Mike Williams; Ian Boomer, for his extensive work in processing the stable isotope samples. Adam Bates, James Hale, Sarah Henshall and Megan Klaar for their advice and support in the field, laboratory and in data analysis; Richard Johnson and Mel Bickerton for their laboratory and technical support, and Kevin Burkhill for his assistance with the production of figures. I would also like to thank the many land owners who granted me permission to access sites, particularly Montgomeryshire Wildlife Trust for allowing the use of Llandinam Gravels. The financial support of the Environment Agency made the entire project possible. Table of contents 1 Exposed Riverine Sediments, the role and value of the resource in English and Welsh rivers 1 1.1 Introduction 2 1.2 Study aims & objectives 6 1.3 Thesis structure 7 1.4 References 9 2 Exposed Riverine Sediments in England and Wales: investigating controls on the abundance and complexity of the habitat 14 2.1 Introduction 15 2.2 Methodology 19 2.3 Results 23 2.3.1 English and Welsh ERS resource 23 2.3.2 Flow regime classifications of river subset 24 2.3.3 Multiple Linear Regression 29 2.4 Discussion 31 2.4.1 Conclusions 34 2.5 References 36 3 The role of habitat connectivity in maintaining complex riparian communities of specialist invertebrates 43 3.1 Introduction 44 3.2 Study aims, objectives and hypotheses 49 3.3 Methodology 50 3.3.1 Study sites and sampling methods 50 i 3.3.2 Statistical analysis 53 3.4 Results 55 3.4.1 Morphological grouping 55 3.4.2 Generalised Linear Modelling 57 3.5 Discussion 60 3.5.1 Conclusions 64 3.6 References 66 4 The long-term value of high flow events in maintaining abundant and diverse riparian invertebrate communities 72 4.1 Introduction 73 4.1.1 Flooding responses of specialist invertebrates 74 4.2 Aim, objectives and hypotheses 76 4.3 Methodology 77 4.4 Results 81 4.5 Discussion 85 4.5.1 Conclusions 89 4.6 References 91 5 The impact of inundation on aquatic nutrient utilisation by riparian beetles 96 5.1 Introduction 97 5.2 Study aim, research questions and hypotheses 104 5.3 Methodology 105 5.3.1 Assessing dietary proportions through stable 105 isotope analysis 5.3.2 Data collection 106 ii 5.3.3 Stable isotope analysis sample preparation 107 5.3.4 Trophic and nutrient proportion analysis 108 5.4 Results 110 5.4.1 Habitat morphology and inundation susceptibility 111 5.4.2 Isotope data 116 5.4.3 Variations in dietary composition 120 5.4.4 Impact of inundation 123 5.4.5 Effect of lateral positioning 123 5.5 Discussion 128 5.5.1 Conclusions 133 5.6 References 134 6 Longitudinal variations in the utilisation of aquatic resources by ground beetles along a 150km length of the River Severn 141 6.1 Introduction 142 6.1.1 Stable isotopes, nutrient sources and dietary composition 145 6.2 Aims, objectives and hypothesis 147 6.3 Methodology 148 6.3.1 Study sites and sample collection 148 6.3.2 Sample processing 149 6.3.3 Data analysis 149 6.4 Results 151 6.5 Discussion 156 6.5.1 Conclusions 163 6.6 References 164 iii 7 Conclusion 171 7.1 ERS and their associated invertebrates: landscape integrity and community cohesion 172 7.2 Limitations observed within the research 177 7.3 Future research suggestions 179 7.4 References 182 8 Appendices 183 Appendix A: Models lying within the 95% confidence interval 184 from multiple linear regressions shown in Chapter 2 Appendix B: Models lying within the 95% confidence interval 187 from generalised linear modelling in Chapter 2 Appendix C: Models lying within the 95% confidence interval 190 from generalised linear modelling in Chapter 4 Appendix D: CD containing English and Welsh ERS database and 192 Coleopteran morphological correlation co-efficients. iv List of figures No. Description Page 1.1 Savage Creek, Denali National Park, Alaska, US; an example of ERS 4 within a braided river. 1.2 Llandinam Gravels, Powys, Wales. ERS deposits formed along a single 5 channel reach of the Upper Severn. 2.1 Channel morphology classifications. 16 2.2 Distribution of gauging station subset in England and Wales. 21 2.3 Distribution of the ERS resource within England and Wales . 23 2.4 Boxplots of indices used to derive river magnitude groupings. 25 2.5 Regime shapes of four derived classes using z-scores of discharge data. 27 2.6 English and Welsh distributions of river magnitude and regime 28 shape classes. 2.7 Scatterplots of environmental factors having positive association 30 with ERS area and density. 3.1 Distribution of rivers and sampling points used to test connectivity 51 variables. 3.2 Box plots of variation in morphological characteristics between 56 Coleopteran functional groups. 4.1 Gravel bars at Llandinam Gravels with long-term Coleopteran dataset. 78 4.2 Inter-annual variations in abundances of specialist rove 81 and ground beetles collected from Llandinam Gravels. 4.3 Abundance trends of rove and ground beetles over time visualised 81 using GAMs. 4.4 Average monthly flows between 2001-2009 recorded at Dolwen 82 gauging station on the upper River Severn. 4.5 Daily flows for 2001-2009 recorded at Dolwen gauging station 84 on the upper River Severn. v 5.1 Nutrient exchanges between aquatic and riparian ecosystems. 98 5.2 Areas sampled for stable isotope analysis on the upper River Severn. 106 5.3 DEM of sampled gravel bars (sites 1-11) at Llandinam. 112 5.4 DEM of samples gravel bars (sites 12-20) at Caersws. 113 5.5 Example illustration of reduction in ERS habitat from a single patch 114 of ERS with sequential 20cm increases in stream depth. 5.6 Daily variations in river depth recorded at Llandinam Gravels, 116 April – October 2009. 5.7 Summary biplots of δ13C and δ15N values for consumers and 117 potential prey. 5.8 Isotopic positions of Coleopteran consumer groups visualised 119 using standard ellipses. 5.9 Probability Density Functions of seasonal variations in consumer diet. 121-22 5.10 Probability Density Functions of variations in species’ dietary 124-25 composition according to inundation pressures. 5.11 Probability Density Functions of lateral variations in 126 headwater ground beetle dietary proportions. 5.12 Conceptual model of functional adaptations predicting distribution 132 and abundance of specialist Coleoptera. 6.1 Sample sites and group positions along the River Severn. 148 6.2 Variation in δ13C and δ15N Coleopteran values according longitudinal 152 sampling position. 6.3 Variation in δ13C and δ15N potential prey values according to 153 longitudinal sampling position. 6.4 Variation in δ13C and δ15N potential prey values according to season 154 of sampling. 6.5 Isotopic positioning of Coleopteran functional groups shown 155 via standard ellipses. 6.6 Probability density functions of longitudinal variations in headwater 157 ground beetle dietary composition. vi 6.7 Probability density functions of longitudinal variations in floodplain 158 ground beetle dietary composition. 6.8 Probability density functions of longitudinal variations in low affinity 159 ground beetle dietary composition. 7.1 Conceptual model of processes structuring specialist beetle 176 assemblages and prey selection. vii List of Tables Table Title Page 2.1 Summary statistics of river magnitude classes (mm month-1). 24 2.2 Combined magnitude and regime shape classes by river. 26 2.3 Summary of best fitting multiple linear regression models 29 predicting ERS area and density. 3.1 Coleopteran functional groups. 57 3.2 Summary of functional group morphology, positioning 57 and connectivity requirements.