THE ECOLOGICAL FACTORS GOVERNING THE PERSISTENCE OF BUTTERFLIES IN URBAN AREAS by ALISON LORAM A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Biosciences The University of Birmingham September 2004 ABSTRACT Previous studies have suggested that availability of high quality habitat rather than habitat connectivity or species mobility was the limiting factor in the distribution of grassland butterflies, but were mostly undertaken on specialist species in rural areas. Consequently, this project tests the hypothesis that the quality of available habitat is more important than patch size or connectivity to the persistence of four grassland butterfly species in the West Midlands conurbation. Two of the study species are widespread (Polyommatus icarus and Coenonympha pamphilus) whilst two have a more restricted distribution (Erynnis tages and Callophrys rubi). However, unlike species with very specific requirements, all are polyphagous and can tolerate a wide range of conditions, making habitat quality difficult to quantify. Several means of assessing habitat quality were developed and tested. A detailed vegetation quadrat sampling method had the best predictive abilities for patch occupancy and summarised the habitat preferences within the urban context. A model based upon habitat quality and connectivity was devised, with the ability to rank each patch according to potential suitability for each species. For all four species, habitat quality accounted significantly for the greatest variance in distribution. Connectivity had only a small significant effect whilst patch area had almost none. This suggests that conservation efforts should be centred upon preserving and improving habitat quality. ACKNOWLEDGEMENTS This project was funded by the Natural Environment Research Council URGENT Program. I wish to thank Andrew Pullin for setting up the project initially, for taking me on as his PhD student and for his enthusiastic supervision, direction, support and honest feedback. I would also like to thank:- Butterfly Conservation, in particular, Jim Asher, Jim Chance and Richard Fox for providing local records and national data from the Butterflies for the New Millenium project; Members of Butterfly Conservation West Midlands Branch, study site managers and conservation officers for information about sites, allowing access and in some cases, for giving “guided tours”; Jenny Joy (Butterfly Conservation) for her friendship, encouragement and ideas; Sara Carvalho and Craig Slawson (Ecorecord) for providing local records and the base map of the region used in the distribution maps; Rob Wilson (University of Leeds) for offering information on calculating connectivity and alpha values; Alan White (University of Birmingham) for initial help with discriminant function analysis. Special thanks to:- Zöe Davies for her friendship and for lots of emails; Roger Dennis for his ideas and encouragement, particularly during the last part of the project, and for comments on the final draft of the thesis; Dave Haslam (Walsall MBC) for continual help with fieldwork techniques and plant identification, particularly in the early stages of the project; Richard Wadsworth (CEH Monkswood) for help with Arcview GIS, ideas on fieldwork methods and comments on the final draft of the thesis; Chris Walker (English Nature) for proof reading the final draft. Most of all, thanks to my husband Ian for assistance with statistical analysis, programs written in Matlab, for constant help, encouragement and support, and at times, apparently unconditional love. CONTENTS CHAPTER 1: Introduction.......................................................................................1 1.1 Changes in UK butterfly distributions.....................................................1 1.2 The importance of urban habitats............................................................2 1.3 A brief history of butterfly conservation.................................................5 1.4 Rare and common butterflies...................................................................7 1.5 Butterflies in urban areas.........................................................................9 1.6 Quality versus size and isolation ...........................................................11 1.7 Aims and objecctives.............................................................................14 1.8 The study area........................................................................................15 1.9 The study species...................................................................................17 1.10 Individual species accounts ...................................................................20 1.10.1 The common blue Polyommatus icarus ....................................20 1.10.2 The small copper Lycaena phlaeas............................................21 1.10.3 The small heath Coenonympha pamphilus................................22 1.10.4 The dingy skipper Erynnis tages ...............................................23 1.10.5 The green hairstreak Callophrys rubi ........................................24 1.11 Scope of thesis.......................................................................................25 1.12 References .............................................................................................27 CHAPTER 2: Development of Sampling Strategies ............................................36 2.1 The problem to be solved ......................................................................36 2.2 Measuring habitat quality......................................................................37 2.3 A GIS approach .....................................................................................41 2.4 Fieldwork...............................................................................................48 2.4.1 Locating patches........................................................................48 2.4.2 To sample or not to sample?......................................................48 2.4.3 Sample scales.............................................................................53 2.4.4 Sampling strategy......................................................................54 2.4.5 Defining patches........................................................................56 2.4.6 Incorporating GIS into methods of site selection ......................58 2.4.7 Datasets......................................................................................61 2.4.8 Mark-release recapture ..............................................................62 2.5 Summary................................................................................................62 2.6 References .............................................................................................64 CHAPTER 3: Determining habitat requirements................................................68 3.1 Introduction ...........................................................................................68 3.2 Methods .................................................................................................70 3.2.1 Fieldwork...................................................................................70 3.2.2 Statistical analyses.....................................................................74 3.3 Results ...................................................................................................76 3.3.1 Detailed Vegetation Quadrat Sampling .....................................77 3.3.2 Patch Attribute Assessment .......................................................88 3.4 Discussion..............................................................................................89 3.4.1 Detailed Vegetation Quadrat Sampling .....................................89 3.4.2 Patch Attribute Assessment .......................................................94 3.5 Conclusion.............................................................................................95 3.6 References .............................................................................................96 CHAPTER 4: Devising a habitat quality index ..................................................100 4.1 Introduction .........................................................................................100 4.2 Aims and objectives ............................................................................102 4.3 Methods ...............................................................................................102 4.3.1 Fieldwork.................................................................................102 4.3.2 Calculation of indices..............................................................104 4.3.3 Assessment of habitat quality indices......................................107 4.4 Results .................................................................................................108 4.4.2 Assessment of habitat quality indices......................................113 4.5 Discussion............................................................................................119 4.5.1 Consistency and reliability of indices......................................119 4.5.2 Accuracy of indices .................................................................120 4.5.3 Sensitivity of indices................................................................121 4.5.4 Practicality of indices..............................................................122 4.5.5 Comparison