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Habitat Fragmentation and Its Effects on Birds and Grasshoppers in Eucalypt Remnants in the Tasmanian Midlands

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Habitat Fragmentation and Its Effects on Birds and Grasshoppers in Eucalypt Remnants in the Tasmanian Midlands Habitat fragmentation and its effects on birds and grasshoppers in eucalypt remnants in the Tasmanian Midlands. by are") Michael MacDonald, BSc (hons Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Geography and Environmental Studies Faculty of Science and Engineering University of Tasmania August, 2001 I declare that this thesis contains no material which has been accepted for a degree or diploma at the University or any other institution, except by way of background information and duly acknowledged in the thesis, and to the best of my knowledge and belief no material previously published or written by another person except where due acknowledgment is made in the text of the thesis. Michael MacDonald Date: zmo( II Authority of Access This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968 Michael MacDonald Date: V(710 ( Ill Abstract In the subhumid Midlands region of Tasmania, forty-seven remnants of eucalypt woodland and dry sclerophyll forest as well as six control sites were surveyed for birds and grasshoppers, in order to examine the responses of these groups to habitat fragmentation. A wide range of characteristics of the remnants (including position in landscape, management regime and vegetation) were related to species richness, diversity and density of the two groups as well as to the distributions of individual species. Remnant size, vegetation structure and tree health all showed significant relationships with bird species richness and diversity. Small remnants with open understorey and high levels of dieback showed radically different species composition than larger ones or those with dense understorey. Where the understorey is open the noisy miner (Manorina melanocephala) is present in colonies and is able to effectively exclude almost all other species by concerted aggressive behaviour. Noisy miner colonies were associated with small remnants but were also present at the edges of larger remnants, where proximity to open country and vegetation structure both predicted their presence. Interspecific competition is considered to be the major determinant of species richness and of many species' distributions in the study area. Analysis of remnants which are not dominated by noisy miner colonies found that area and isolation were significantly correlated with species richness and diversity,. although larger remnants did not have more species at a given point. Summer migrants and nomadic species are considered to be more sensitive to habitat fragmentation as a result of the presence of noisy miner colonies in the fragmented habitat. Interspecific competition is considered to be the driving force behind avifaunal trends in the study area. Grasshopper species richness was not related to any of the variables measured, but diversity was higher in remnants in better condition, while density was higher in remnants in poor condition. Common grasshopper species responded to a range of variables. Management of remnants for conservation of avifaunal and grasshopper values is discussed. In the context of avifauna conservation, it is suggested that although larger remnants are more likely to support a healthy suite of bird species, the presence of a dense understorey in smaller remnants can improve their conservation value. Both of these options are likely to also lead to the maintenance of forest- and woodland- dwelling grasshopper species. iv Acknowledgments I would like to thank my supervisor, Jamie Kirkpatrick, for his patience, assistance arid encouragement in this research. Peter McQuillan identified grasshoppers and provided considerable assistance in understanding the results of the grasshopper collection. All landowners involved have been helpful in allowing me access to their properties. Other postgraduate students have provided advice and help at times. In particular, Mona Loofs has helped me to maintain my sanity. I wish to thank my family for their support over the past five years. Anneli MacDonald has inspired me and enabled me to finish this and keep my promises. Contents Page Title Statement of authenticity ii Declaration iii Abstract iv Acknowledgments Table of contents vi 1 A review of the effects of habitat fragmentation 1 1.1 Introduction 1 1.2 Island biogeography and other theories 6 1.3 Forest fragmentation in Australia 11 1.4 The Tasmanian Midlands 12 1.5 Thesis aims 14 2 General methods 17 2.1 Study area 17 2.2 Bird and grasshopper surveys 19 2.3 Independent variables 21 2.4 Data analysis 22 3 Birds of eucalypt remnants in Tasmania's Midlands 27 3.1 Introduction 27 3.1.1 Birds in fragmented forests 27 3.1.2 The Australian situation 33 3.1.3 Avifauna of the Tasmanian Midlands 35 3.2 Methods 38 3.2.1 Bird assemblages 38 3.2.2 Community-level responses variables 39 3.2.3 Bird species' distributions 39 3.3 Results 40 3.3.1 Classification 41 3.3.2 Bird assemblages, independent variables and community-level responses 44 3.3.3 Community-level responses 48 3.3.4 Community-level responses in the absence of noisy miner colonies 49 3.3.5 Species' distributions and abundances and independent variables 54 3.4 Discussion 69 3.4.1 Species observed 69 3.4.2 Bird assemblages 71 3.4.3 Community-level responses 76 3.4.4 Species' responses 81 3.4.5 Conclusion 83 4 Dieback in eucalypt remnants in Tasmania's Midlands 87 4.1 Introduction 87 4.2 Methods 93 4.2.1 Dieback measures 94 4.2.2 Data analysis 94 4.3 Results 94 4.4 Discussion 98 5 Seasonal movements of birds in eucalypt remnants in Tasmania's Midlands 103 5.1 Introduction 103 5.2 Methods 107 vi Contents (cont.) Page 5.3 Results 109 5.3.1 Climatic data 109 5.3.2 Between-year variation 112 5.3.3 Similarity index 113 5.3.4 Seasonal variation 114 5.3.5 Migratory guilds and independent variables 116 5.4 Discussion 119 5.4.1 Between-year differences 119 5.4.2 Seasonal differences 120 5.4.3 Migratory guilds and independent variables 122 5.4.4 Conclusion 124 6 Edge-interior differences in the avifauna of eucalypt remnants in Tasmania's Midlands 126 6.1 Introduction 126 6.2 Methods 128 6.3 Results 129 6.3.1 Community-level responses and independent variables 130 6.3.2 Species' responses 133 6.4 Discussion 134 7 Grasshoppers of eucalypt remnant in Tasmania's Midlands 138 7.1 Introduction 138 7.2 Methods 141 7.2.1 Grasshopper surveys 141 7.2.2 Data analysis 143 7.3 Results 143 7.3.1 Species observed 143 7.3.2 Community-level responses and independent variables 144 7.3.3 Species distributions and independent variables 145 7.4 Discussion 149 7.4.1 Community-level responses 150 7.4.2 Species distributions 151 7.4.3 Comparison with avifaunal trends 152 7.4.4 Conclusion 153 8 Conclusion 155 8.1 Introduction 155 8.2 Theories of species richness 155 8.3 Comparisons between birds and grasshoppers 158 8.4 Management implications 158 9 References 165 Appendix One: Remnant details 187 Appendix Two: Bird species recorded 189 Appendix Three: Grasshopper species recorded 193 vii Contents (cont.) Page Figures Figure 2.1 Location of remnant- study sites 18 Figure 3.1 Classification of remnants into avifaunal assemblages 43 Figure 3.2 Ordination of remnants according to avifauna 43 Figure 5.1 Mean maximum a-ir temperatures for 1996-1998 and long term averages for Launceston Airport 110 Figure 5.2 Monthly rainfall for 1996-1998 and long term averages for Oadands Post Office 111 Figure 6.2 Classification of 200 m segments in avifaunal assemblages 129 Tables Page Table 2.1 A complete list of independent variables 25 Table 3.1 Summary statistics for bird species richness, diversity and density 41 Table 3.2 Contingency tables for variables which differed significantly from expected values 45 Table 3.3 Means and standard deviations of continuous variables and chi-squared analysis of ordinal variables for bird assemblages 46 Table 3.4 Significant relationships between independent variables and bird community-level responses 50 Table 3.5 Significant relationships between independent variables and bird community-level responses (excluding noisy miner colonies) 52 Table 3.6 Bird species and those variables which differ according to their distribution and abundance 55 Table 4.1 Values and standard deviation of measures of tree health for remnants dominated by noisy miner colonies and other remnants 95 Table 4.2 Significant relationships between independent variables and measures of tree health 96 Table 4.3 Values and standard deviations of independent variables which differed significantly according to floristic group 97 Table 4.4 Values and standard deviations of mean dieback score for eucalypt species and dbh classes using amalgamated data set 97 Table 5.1 Between-year differences for community-level responses, bird species, and migratory, foraging and food preference guilds 112 Table 5.2 Significant relationships between similarity index and independent variables 113 Table 5.3 Between-season differences for community-level responses, bird species, and migratory, foraging and food preference guilds • 114 Table 5.4 Significant relationships between migratory guilds and independent variables 117 Table 6.1 Contingency tables for the distribution of noisy miner colonies in edge and interior segments for (A) whole data set and (B) remnants - supporting miner colonies as well as other assemblages 130 viii Contents (cont.) Tables Page Table 6.2 Values and standard deviations for independent variables and community-level responses between edge and interior segments 131 Table 6.3 Values and standard deviations for independent variables between miner dominated segments and other segments within the same remnants 132 Table 6.4 Abundance values and standard deviations for species which differed significandy between edge and interior segments 133 Table 7.1 Significant relationships between independent variables and grasshopper community-level responses 147 Table 7.2 Grasshopper species and those variables which differ according to their presence or abundance 148 ix 1.
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