Biology of Termites: a Modern Synthesis (eBook)

Foreword 6

7 
Preface 8
Contents 10
Contributors 12
1 An Introduction to Termites: Biology, Taxonomy and Functional Morphology 14
1.1 Introduction 14
1.2 Diversity, Taxonomy, Classification 15
1.3 The Colony 16
1.4 The Colony as (Super)organism 17
1.5 Reproduction and Dispersal: Alates 19
1.5.1 Head (Figs. 1.1 and 1.2) 20
1.5.2 Thorax (Fig. 1.1) 20
1.5.3 Wings (Figs. 1.1 and 1.3) 22
1.5.4 Legs (Fig. 1.4) 24
1.5.5 Abdomen 24
1.6 Worker Morphology 26
1.7 Construction, Feeding and Tending 26
1.7.1 Feeding 26
1.7.2 Nursing 30
1.8 Active Defence: Soldiers 31
1.9 Protection, Stability, Fortification: Nests and Mounds 33
1.9.1 Protection and Stability 34
1.9.2 Fortification 35
1.10 Conclusions 36
References 37
2 Termite Phylogenetics and Co-cladogenesis with Symbionts 40
2.1 Introduction 40
2.2 Phylogenetic Origins of the Termites 41
2.2.1 Pre-cladistic Studies of Termite Relatives 41
2.2.2 Cladistic Analyses 42
2.3 Co-cladogenesis Between Cockroaches, Termites, and Their Symbionts 44
2.3.1 Blattabacterium 44
2.3.2 Cellulolytic Flagellates 44
2.4 Fossil History and Key Events Leading to the Origin of Termites 46
2.5 Taxonomic Implications of the Phylogenetic Position of Termites 47
2.6 Termite Phylogeny: Morphological Character Sets 47
2.6.1 Alate Morphology 47
2.6.2 Soldier Morphology 48
2.6.3 Worker-Imago Mandible Morphology 48
2.6.4 Worker Gut Anatomy 50
2.6.5 Other Character Sets 50
2.7 Phylogenetic and Taxonomic Relationships Among Termites 50
2.7.1 Termites with Flagellates (The So-Called ''Lower Termites'') 52
2.7.2 Co-cladogenesis of Cellulolytic Flagellates Among Termites 56
2.7.3 Relationships Within Termitidae (The So-Called ''Higher Termites'') 57
2.7.4 Co-cladogenesis Between Fungus-Growing Termites and Termitomyces 57
2.8 Conclusions 58
References 59
3 Evolution and Function of Endogenous Termite Cellulases 64
3.1 Introduction 64
3.2 Cellulose and Cellulases 65
3.2.1 Cellulase Components 65
3.2.2 Complete vs. Incomplete Cellulases 66
3.2.3 Cellulases Are Glycolsyl Hydrolases 67
3.3 A Brief History of Termite Cellulase Research 67
3.4 Discovery of Endogenous Cellulase Genes and Their Evolutionary Origins 68
3.5 Endogenous Endoglucanase and -Glucosidase Copy Number and Expression in Termites 71
3.5.1 Endoglucanases 71
3.5.2 -Glucosidase 73
3.6 Functional Significance of Endogenous Cellulases 73
3.7 Caste Specific Production of Cellulase Genes 76
3.8 Conclusions 77
References 78
4 Altricial Development in Wood-Feeding Cockroaches: The Key Antecedent of Termite Eusociality 81
4.1 Introduction 82
4.1.1 Evolution of Development 83
4.1.2 Evolution of Termite Eusociality: A Two Stage Process 84
4.2 Altricial Development 85
4.2.1 Altricial Development in Wood Feeding Cockroaches 86
4.2.2 Food and Protection 89
4.2.3 Evolution of Dependence 90
4.2.4 Parental Care as Selective Environment 90
4.3 Altricial Offspring: Necessary Precedent to Eusociality 91
4.3.1 Raising Altricial Offspring: Economics 91
4.3.2 Raising Altricial Offspring: Temporal Dimension 92
4.3.3 Stage 1: The Transition To Alloparental Care 93
4.3.3.1 Consequences for Parents 94
4.3.3.2 Consequences for Alloparents 94
4.3.3.3 Origins of Alloparental Behavior 95
4.3.3.4 Consequences for the Family 96
4.3.4 Stage 2: Soldiers 98
4.4 Altricial Development Becomes the Norm 99
4.4.1 Vulnerability 99
4.4.2 Developmental Plasticity and Alternative Phenotypes 100
4.5 Conclusions 100
References 101
5 Eusocial Evolution in Termites and Hymenoptera 108
5.1 Introduction 108
5.2 Evolution from Subsocial Ancestors 110
5.2.1 Origins of Eusociality 110
5.2.2 Differences Between Hymenoptera and Isoptera Affecting Eusocial Evolution 111
5.3 Forms of Helpers 113
5.3.1 Helpers Retaining Full Reproductive Potential 114
5.3.2 Soldiers 115
5.3.3 Subfertile or Sterile Workers 117
5.4 Predispositions for Eusociality 117
5.4.1 Extended Parental Care and Parent-Offspring Interaction 118
5.4.2 Incentives for Offspring to Remain at the Nest 119
5.4.3 Valuable, Protected Nests 120
5.4.4 Weaponry 120
5.4.5 Efficiency of Foragers 122
5.4.6 Relatedness Asymmetries 122
5.4.7 Mating Behavior and the Number of Reproductives 123
5.4.8 High Chromosome Numbers 124
5.4.9 Disease Resistance 124
5.5 Selective Processes Promoting Eusocial Helpers 124
5.5.1 Theories Focused on Kin Selection and Indirect Fitness 125
5.5.1.1 Intrinsic Benefits to the Group 126
5.5.1.2 Transactional Skew 126
5.5.1.3 Assured Fitness Returns 127
5.5.2 Theories Focused on Group Selection and Mutualisms 127
5.5.2.1 Group Selection or Mutualism Between Individuals 127
5.5.2.2 Future Reproductive and Inheritance Opportunities 128
5.5.3 Theories Focused on Coercion and Parental Manipulation 130
5.5.3.1 Manipulation that Favors Parental Fitness at Cost to Helper Offspring 130
5.5.3.2 Subfertility 131
5.5.3.3 Within Group Competition for Reproductive Opportunities 132
5.6 Synthesis 132
5.6.1 Similarities Suggesting Common Principles 132
5.6.2 Distinctions Suggesting Unique Properties Within Each Group 133
References 134
6 Social Organisation and the Status of Workers in Termites 144
6.1 Introduction 145
6.1.1 The Soldier Caste 145
6.1.2 The ''Worker'' Caste 145
6.1.2.1 Larvae and Nymphs 146
6.1.2.2 Pseudergates 146
6.1.2.3 True Workers 147
6.1.2.4 Difficulties in the Interpretation of Termite Castes 147
6.2 Mastotermitidae 149
6.3 Wood-Dwelling Termites 149
6.3.1 Kalotermitidae 150
6.3.2 Termopsidae 151
6.4 Hodotermitidae 152
6.5 Rhinotermitidae, Serritermitidae and Termitidae 152
6.5.1 Psammotermes 152
6.5.2 Prorhinotermes 153
6.5.3 Termitogeton 153
6.5.4 Glossotermes 153
6.5.5 Reticulitermes 154
6.5.6 Coptotermes 155
6.5.7 Rhinotermitinae 156
6.5.8 Termitidae 156
6.6 Origin and Evolution of the Worker Caste 157
6.6.1 Evolutionary Transitions Between Pseudergates and Workers 157
6.6.1.1 Facultative Pseudergates Sensu Stricto in Small-Colony Kalotermitidae 158
6.6.1.2 Functional Caste: Pseudergates Sensu Lato in Basal Rhinotermitidae 158
6.6.1.3 Occasional Pseudergates Sensu Stricto Amid True Workers 159
6.6.1.4 Origins of True Workers 159
6.6.2 Proximate Developmental and Regulatory Mechanisms 160
6.6.3 Ultimate Causes of Worker Caste Evolution 163
6.6.3.1 Properties of Wood as Habitat and Food Source 163
6.6.3.2 Kin-Selected Benefits of Helping 165
6.6.3.3 Direct Benefits of Inheritance 166
6.6.3.4 Why Be a False Worker Rather than a True One? 167
6.7 Conclusion: What Is a Worker 168
References 169
7 Ecology, Behavior and Evolution of Disease Resistance in Termites 176
7.1 Introduction 176
7.2 Phylogeny, Eusociality, and the Evolution of Disease Resistance in Termites 178
7.3 Termite Microbial Ecology, Disease Risk and Immunocompetence 180
7.3.1 Nesting Ecology and Exposure to Disease Agents 180
7.3.2 Immunocompetence in Termites 182
7.3.2.1 Antibiotic Prophylaxis 182
7.3.2.2 Immune Function in Termites 183
7.3.3 Immunity in Individuals 183
7.3.3.1 Cellular Immune Responses 183
7.3.3.2 Phagocytosis 184
7.3.3.3 Encapsulation and the Phenoloxidase Proteolytic Cascade 185
7.3.3.4 Humoral Immune Defenses 186
7.3.4 Evolution of Innate Immune Genes in Termites 189
7.4 Social Behavior and Infection Control 190
7.4.1 Social Mediation of Immunocompetence 191
7.5 Termite Life History, Genetic Diversity and Disease Resistance 193
7.6 Disease and Colony Foundation 194
7.7 Conclusions 195
References 196
8 Comparative Biology of Fungus Cultivation in Termites and Ants 203
8.1 Introduction 203
8.2 Evolutionary History of Fungiculture 204
8.3 Colony Foundation and Establishment of the Fungus Garden 206
8.4 Role of Fungal Symbiont 208
8.5 Fungus Garden Protection 211
8.6 Evolutionary Stability 213
8.7 Concluding Remarks 215
References 215
9 Molecular Basis Underlying Caste Differentiation in Termites 221
9.1 Introduction 221
9.2 A Historical View of Classic Work on Caste Determination and Differentiation 222
9.2.1 Castes in Termites 222
9.2.2 Division of Labor and Caste Developmental Patterns 222
9.2.3 Classical Work on Caste Differentiation 223
9.3 Screening of Genes Responsible for Caste Differentiation: Gene Discovery and Genomics 224
9.3.1 Molecular and Genomic Approaches to Study Termite Caste Differentiation 224
9.3.2 Differential Display 224
9.3.3 Polyphenic Library and Arrays 226
9.3.4 Representation Difference Analysis (RDA) 228
9.3.5 Identification of Cytochrome P450 Genes 228
9.3.6 Cytochrome c Oxidase Subunit III: Reticulitermes santonensis and flavipes 229
9.3.7 Shotgun Library Sequencing 230
9.4 Investigations of Gene Functions in Termites: Functional Genomics 230
9.4.1 Gene Expression Changes in Response to Experimental Treatments 231
9.4.1.1 Experimental Treatments 231
9.4.1.2 Pleiotropic Effects 231
9.4.2 Controlling for Colony and Environmental Effects 232
9.4.2.1 Colony Release Effects 232
9.4.2.2 Environmental Effects 232
9.4.3 RNA Interference 233
9.4.3.1 RNAi in Termites 233
9.4.3.2 RNAi Target Genes and Silencing Options 234
9.4.3.3 Phenotypic Impacts of RNAi 234
9.4.3.4 Sub-organismal Impacts of RNAi 235
9.4.4 Protein Studies: Proteomics 235
9.5 Hormonal Regulation of Caste Differentiation 236
9.5.1 Overview of JH Literature in the Last Five Decades 236
9.5.2 Multiple Roles for Hormones, Especially JH (Soldier Differentiation vs. Vitellogenesis) 237
9.5.2.1 JH in Soldier Caste Differentiation 237
9.5.2.2 JH and Ecdysteroid Roles in Vitellogenesis 238
9.5.3 Recent Analytical Identification of JH: Quantification of JH Titer and Related Gene Expression 238
9.5.4 Insulin Signaling in Termite Caste Differentiation 239
9.6 Morphogenesis in Caste Differentiation 239
9.6.1 Evo-Devo and Termites (Modularity and Heterochrony) 239
9.6.2 Histological and Morphological Changes During Soldier Morphogenesis 240
9.6.3 Factors Responsible for Morphogenetic Changes 242
9.7 Social Regulation of Caste Ratios 243
9.7.1 Primer and Releaser Pheromones: An Overview 243
9.7.2 Termite Hexamerins as a Caste Regulatory Mechanism 244
9.7.2.1 Experimental Summary 244
9.7.2.2 Hexamerins and Co-option of a Juvenile Ground Plan 245
9.7.2.3 Cockroach Hexamerins as a Model 247
9.7.3 Caste-Specific Signals Secreted from Exocrine Glands 247
9.8 Sociogenomics in Termites 248
9.8.1 Sociogenomics as Defined by Robinson 248
9.8.2 Similar Genes Identified Across Termite Species 249
9.8.2.1 Hexamerin Genes 249
9.8.2.2 Vitellogenin Genes 249
9.8.2.3 P450 Genes 250
9.8.2.4 Larval Cuticle Protein (LCP) Genes 250
9.8.2.5 Lignocellulase Genes 250
9.8.3 Genome Sizes in Termites 251
9.8.4 The Need for a Genome Sequence and Other Robust Genomic Tools and Resources 251
9.9 Conclusions and Perspectives 252
References 253
10 Sexual and Asexual Reproduction in Termites 264
10.1 Introduction 264
10.2 Facultative Parthenogenesis in Maleless Colony Foundation 267
10.3 Mechanism of Termite Parthenogenesis 269
10.3.1 Automixis with Terminal Fusion 271
10.3.2 Developmental Constraints 272
10.4 Asexual Queen Succession (AQS) 272
10.4.1 Composition of Reproductives in Field Colonies 272
10.4.2 The Paradox of the King-Daughter Inbreeding Hypothesis 274
10.4.3 Parthenogenesis for Secondary Queens, but Sex for Workers and Alates 275
10.5 Parthenogenesis and Recessive Deleterious Genes 278
10.5.1 Purging Selection 278
10.5.2 Inbreeding Preadaptation Hypothesis for the Evolution of Thelytoky 279
10.6 Genetic Basis of AQS 279
10.6.1 Selfish Genetic Elements Involved in AQS 279
10.6.2 Genetic Priority of Parthenogens To Be Secondary Queens 281
10.7 Comparison of AQS Systems Between Termites and Ants 281
10.8 Clues to Find New AQS Species 283
References 283
11 Pheromones and Chemical Ecology of Dispersal and Foraging in Termites 287
11.1 Introduction 288
11.2 Dispersal 288
11.2.1 Dispersal Sequence 288
11.2.2 Sex-Pairing Pheromone Glands 291
11.2.2.1 Tergal Glands 291
11.2.2.2 Sternal Gland 292
11.2.2.3 Posterior Sternal Glands 292
11.2.2.4 Pleural Glands 293
11.2.3 Chemical Nature of Sex-Pairing Pheromones 293
11.2.4 Trail-Following Pheromones Involved in Tandem Behaviour 299
11.2.5 Sex-Pairing Pheromones and Reproductive Isolation 299
11.3 Foraging 300
11.3.1 Trails and Trail-Following Pheromones 300
11.3.1.1 Trails and Ecological Life Types 301
11.3.1.2 Exploratory Trails and Foraging Trails 302
11.3.1.3 Trails and Polyethism 302
11.3.1.4 Trail Persistence and Trail-Following Pheromone Longevity 303
11.3.1.5 Trail Polarity 303
11.3.1.6 Territoriality and Trail-Following Pheromones 305
11.3.1.7 Semiochemicals on Foraging Sites 305
11.3.2 Trail-Following Pheromone Glands 306
11.3.3 Chemical Nature of Trail-Following Pheromones 306
11.3.4 Biological Activity of Trail-Following Pheromones 313
11.3.5 Chemical Nature and Behavioural Effects of Trail-Following Pheromones 314
11.3.6 Species-Specificity of Trail-Following Pheromones 314
11.3.7 Evolution of Trail-Following Pheromones and Phylogeny 315
11.4 Pheromonal Parsimony 317
11.5 Conclusions 318
References 319
12 Genetic Structure of Termite Colonies and Populations 329
12.1 Introduction 330
12.2 Genetic Tools 331
12.2.1 Allozyme Markers 331
12.2.2 Mitochondrial Genes 332
12.2.3 Nuclear Gene Sequences 332
12.2.4 Multilocus DNA Fingerprinting 332
12.2.5 Microsatellite Genotyping 333
12.3 Colony Genetic Structure 334
12.3.1 Colony Founding 334
12.3.1.1 Relatedness of Colony Founders 334
12.3.1.2 Number and Relatedness of Colony Founders 336
12.3.2 Colony Breeding Structure 337
12.3.2.1 Simple Families 340
12.3.2.2 Extended Families 340
12.3.2.3 Mixed Family Colonies 341
12.3.2.4 Geographic Variation in Colony Breeding Structure 343
12.4 Population Genetic Structure 344
12.4.1 Small-Scale Structure and the Issue of Budding 344
12.4.2 Large-Scale Structure 344
12.5 Phylogeography 345
12.6 Population Genetics of Invasive Species 346
References 348
13 Termite Mound Architecture, from Function to Construction 356
13.1 Introduction 356
13.2 Function and Functional Significance of Termite Mound Architecture 359
13.2.1 Fungus Growing Termites 359
13.2.1.1 Macrotermes bellicosus 361
13.2.1.2 Macrotermes michaelseni 365
13.2.1.3 Macrotermitinae with Open Mounds 366
13.2.2 Magnetic Termites 368
13.2.2.1 Why Are Magnetic Termite Mounds Orientated North?South? 369
13.2.2.2 How Can the Variation in Exact Orientation Be Explained Between Different Areas? 369
13.2.2.3 The Open Question: Why Are Mounds Elongated? 370
13.2.3 Conclusion on Mound Function 371
13.3 Proximate Mechanisms of Mound Building 373
13.3.1 Description of Royal Cell Re-construction 373
13.3.2 Proposed Building Mechanisms 374
13.4 Concluding Remarks 375
References 376
14 Morphology, Physiology, Biochemistry and Functional Design of the Termite Gut: An Evolutionary Wonderland 381
14.1 Introduction 381
14.2 Structure and Design: New Insights 384
14.2.1 Noirot's Synoptic Reviews 384
14.2.2 Donovan's Feeding Group Classification 385
14.2.3 Gut Configurations, the Enteric Valve and Particle Separation: Some Progress 387
14.2.4 Processing and Roles of Faecal Material 390
14.2.5 Accommodation of Microorganisms 392
14.3 Physiology 395
14.4 Biochemistry 396
14.4.1 Overview of Termite Digestion 396
14.4.2 Degradation of Cellulose, Non-cellulosic Polysaccharides and Lignin 399
14.4.3 Digestion in Fungus-Growers 401
14.4.4 Lysozyme and Proteases 404
14.4.5 How Do Soil-Feeders Work? 404
14.5 An Overarching Hypothesis of Evolution 408
References 409
15 Diversity, Structure, and Evolution of the Termite Gut Microbial Community 419
15.1 Introduction 419
15.2 Molecular Phylogeny and Evolution of Protists 420
15.2.1 Trends in Molecular Studies 420
15.2.2 Parabasalid Symbionts 421
15.2.3 Oxymonad Symbionts 422
15.3 Bacterial Diversity 423
15.3.1 Diversity Estimation 423
15.3.2 Novelty of Gut Bacteria 424
15.3.3 Composition of Bacterial Groups 424
15.4 Archaeal Diversity 425
15.5 Comparisons Among Host Termites 426
15.6 Spatial Distributions in Lower Termites 428
15.7 Protist-Prokaryote Associations 429
15.7.1 Methanogenic Archaea 429
15.7.2 Spirochetal Ectosymbionts 429
15.7.3 Motility Symbiosis 430
15.7.4 Bacteroidales Ectosymbionts 430
15.7.5 Endosymbiotic Bacteroidales 432
15.7.6 Endosymbiotic Endomicrobia 432
15.7.7 Associations of Multiple Species 433
15.7.8 Coevolution of Protists and Their Symbionts 433
15.7.9 Complete Genome of the Endosymbionts 435
15.8 Features of Microbial Communities in Higher Termites 435
15.8.1 Structure of the Microbial Community 435
15.8.2 Metagenomic Analysis of a Higher Termite 436
15.9 Conclusions and Perspective 437
References 438
16 Role of the Termite Gut Microbiota in Symbiotic Digestion 445
16.1 Introduction 446
16.2 Digestion of Wood Polysaccharides 447
16.2.1 The Dual Cellulolytic System of Lower Termites 447
16.2.2 Role of Bacteria in Fiber Digestion 449
16.3 The Anaerobic Food Web 451
16.3.1 Fermentative Degradation of Carbohydrates 451
16.3.2 Hydrogen as Central Intermediate 454
16.3.3 Methanogenesis 454
16.3.3.1 Reductive Acetogenesis 456
16.3.4 Anaerobic Respirations 457
16.4 Termite Guts as Gradient Systems 458
16.4.1 Spatial Separation of Microbial Processes 458
16.4.2 Effects of Oxygen on Hindgut Metabolism 460
16.4.3 Absence of Methane Oxidation in Termites 462
16.5 Role of the Gut Microbiota in Nitrogen Metabolism 462
16.5.1 Nitrogen Recycling in Wood-Feeding Termites 463
16.5.2 Nitrogen Fixation by Gut Bacteria 464
16.5.3 Upgrading of Nitrogen Quality 466
16.5.4 Nitrogen Metabolism of the Flagellate Symbionts 466
16.6 Digestion of Soil Organic Matter 468
16.6.1 Nutritional Basis of Soil-Feeding Termites 468
16.6.2 Functional Compartmentalization of the Gut 469
16.7 Do Termites Degrade Lignin 470
16.8 Conclusions 472
References 473
17 Global Biogeography of Termites: A Compilation of Sources 482
17.1 Introduction 483
17.2 Termite Functional and Taxonomic Classification 484
17.3 Exemplar Assemblages 485
17.4 Taxonomic Richness 486
17.5 Comparison of Assemblages Within Biomes: Some Preliminary Observations 497
17.6 Implications of Varying Assemblage Structures for Termite Mediated Decomposition in Different Biomes 498
17.7 Conclusions 499
References 500
18 Termites as Pests of Agriculture 504
18.1 Introduction 504
18.2 Damage to Tropical Crops 506
18.2.1 Forestry 506
18.2.1.1 Eucalyptus 506
18.2.1.2 Coconuts and Palms 506
18.2.1.3 Fruit Trees 507
18.2.2 Sugar Crops 507
18.2.3 Cereal Crops 508
18.2.3.1 Rice 508
18.2.3.2 Maize 508
18.2.3.3 Wheat 508
18.2.3.4 Sorghum 509
18.2.4 Oil Crops 509
18.2.4.1 Groundnut 509
18.2.4.2 Castor Oil 509
18.2.5 Beverage Crops 509
18.2.5.1 Coffee 509
18.2.5.2 Tea 510
18.2.5.3 Cocoa 510
18.2.6 Pastures 510
18.2.7 Tuber Crops 510
18.2.7.1 Yam 510
18.2.7.2 Manioc (Cassava) 510
18.2.8 Market Gardens 511
18.2.9 Fibre Crops 511
18.3 Chemical Control 511
18.3.1 Use of Insecticides 511
18.3.2 Chitin Synthesis Inhibitor 512
18.3.3 Fungicides 512
18.4 Control by Non-Chemical Means 513
18.4.1 Cultural Methods 513
18.4.1.1 Practices Improving Plant Vigour 513
18.4.1.2 Practices to Reduce Termite Numbers 514
18.5 Biological Control 514
18.5.1 Viruses 514
18.5.1.1 Bacteria 514
18.5.2 Fungi 515
18.5.3 Protists 515
18.5.4 Nematodes 515
18.6 Conclusions 515
References 517
19 Invasive Termites 523
19.1 Introduction 523
19.2 Definitions 524
19.3 List of Invasive Species 526
19.3.1 New Species 527
19.3.1.1 Kalotermitidae 527
19.3.1.2 Rhinotermitidae 536
19.3.1.3 Termitidae 537
19.3.2 Species with Larger Distributions 537
19.3.2.1 Mastotermitidae 537
19.3.2.2 Kalotermitidae 538
19.3.2.3 Rhinotermitidae 539
19.3.3 Species with No Change 540
19.3.3.1 Termopsidae 541
19.3.3.2 Kalotermitidae 541
19.3.3.3 Rhinotermitidae 541
19.3.4 Species No Longer Considered Invasive 542
19.3.4.1 Kalotermitidae 542
19.3.4.2 Rhinotermitidae 542
19.4 Characteristics of Invasive Species 542
19.4.1 Wood-Feeding 542
19.4.2 Nesting Habit 545
19.4.3 Secondary Reproductives 546
19.4.4 Kalotermitidae and Rhinotermitidae 547
19.5 Invaded Habitats 550
19.5.1 Islands and Coasts 550
19.5.2 Habitat Type and Resilience 553
19.6 Source Habitats of Invasive Species 555
19.7 Future Invasions 556
References 558
Index 567