Island Biogeography Ecology, Evolution, and Conservation

ROBERT J. WHITTAKER School of Geography, University of Oxford

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Technische Universitat Darmstadt FACHBEREICH 10 —BIOLOGIE — BJbliothek SchnittspahnstraBe 10 D-6 4 2 8 7 D a r m s t a d t

•»•••••••cats I OXFORD NEW YORK TOKYO

OXFORD UNIVERSITY PRESS 1998

Contents 1

The natural laboratory paradigm

1

2

Island environments

7

2.1 2.2

2.6

Types of islands . / •> ' J • - • "• Modes of origin 2.2.1 Plate boundary islands " '; • ~>: . : 2.2.2 Islands in intra-plate locations . . . J Environmental changes over long time-scales • 2.3.1 Changes kurelative sea level—reefs, atolls, and-guyots •'• • ' '• -'•' : 2.3.2 Eustatic changes in sea level ' " • v ' 2.3.3 Climate change on islands ' ': ' ' ' 2.3.4 Case study of an island at sea: the environmental history of Jamaica over the past 50 million years * ' ' Physical environment of islands , . 2.4.1 Topographic characteristics 2.4.2 Climatic characteristics 2.4.3 Water resources " ' " ''' : " ' ' ' 2.4.4 Tracks in the ocean ( . , Natural disturbance on islands , . . . ••••.... 2.5.1 Magnitude and frequency ••»••••••. 2.5.2 Continued volcanism . Summary "

20 21 21 23 25 26 26 29 31 31

3

Biodiversity h o t - s p o t s • •

33

3.1 3.2 3.3 3.4 3.5

3.6 3.7

Introduction: the global significance of island biodiversity • : . . : « . '.. ' '• T h e split between continental and oceanic islands .revisited -• >• • . Species poverty .' .,' ,: • , . • . •_. • . , '. Disharmony, filters, and regional biogeography , •_ ' •"..,• : . Endemicity . •• ••• ,. . • .•>, . . .-,-•• • .• . . .:• : ; 3.5.1 N e o - a n d palaeo-endemicity ••.>.>'•:..'.-..'•-.. . r- • . .• 3.5.2 Endemic plants • •> • • • - ' " •• 3.5.3 Endemic animals , 4 Extinct island endemics: a cautionary note Summary

33 33 34 35 43 43 44 6 49 51

4

Speciation and the island condition

53

4.1 4.2

Introduction: first know" your species The species concept and its place in phylogeny

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2.4

2.5

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53 54

viii 4.3

Contents

4.5 4.6

The geographical contexts of speciation events 4.3.1 Distributional context ' 4.3.2 Locational context—island or mainland change? Mechanisms of speciation 4.4.1 Allopatric or geographical speciation 4.4.2 Competitive speciation 4.4.3 Polyploidy One more framework: tree form or phylogeny Summary

5

Arrival and change

5.1 5.2 5.3

5.4

Founder effects, genetic drift, and bottlenecks Sex on islands ' x Niche shifts 5.3.1 The loss of dispersability 5.3.2 Gigantism and nanism 5.3.3 Character displacement 5.3.4 Ecological release ..-....-.. 5.3.5 Other niche shifts and syndromes Summary (

6

Emergent models of island evolution

4.4

6.1 6.2

/ 6.3

6.4 ••

6.5

Speciation with little or no radiation: anagenesis nThe taxon cycle , " 6 . 2 . 1 Melanesian ants .. .. ; 6.2.2 Caribbean birds 6.2.3 Caribbean anoles 6.2.4 Evaluation Adaptive radiation 6.3.1 Darwin's finches and the Hawaiian honeycreeper-finches 6.3.2 Hawaiian crickets and drosophilids 6.3.3 Adaptive radiation in plants Observations on the forcing factors of island evolution 6.4.1 Environmental change as a driving force 6.4.2 Rates of speciation vary through time and between taxa 6.4.3 Dispersal ability and endemism 6.4.4 Biogeographical hierarchies and island evolutionary models Summary

7

Species numbers games

7.1 7.2

Introduction The development of the equilibrium theory of island biogeography

Contents

ix

7.5

7.2.1 Species-area patterns .. , v •. . .• 7.2.2 Species abundance distributions 7.2.3 The distance effect 7.2.4 Turnover, the core theory (ETIB) and its immediate derivatives r ; .' Spatial analyses of island species number . '. . 7.3.1 Area and habitat diversity ' . . • • • . . - . •• ; •. -• / 7.3.2 The habitat-unit model . !• .-.•; ..' 7.3.3 Competing hypotheses for the species-area effect : 7.3.4 Area is not always that important • • •' • 7.3.5 Species-energy theory * . . . • r c 7.3.6 Isolation and distance \ s . 7.3.7 Species-area relationships in remote .archipelagos -^ .' 7.3.8 Scale effects • • .• l Turnover --.O ' . . • • ' 7.4.1 Pseudoturnover and cryptoturnover. / .• \ r 7.4.2 When is an island in equilibrium? ". • r . 7.4.3 Propagules and pools • • 7.4.4 The rescue effect and the effect of island area on immigration rate 7.4.5 The path to equilibrium *• . 7.4.6 What causes extinctions? ,:,.'•'.. ] 7.4.7 Forms of equilibria and non-equilibria' < ' '. ; • Summary " • . •-*'.• •

8

Community assembly and dynamics

144

Introduction Island assembly .theory . . . . . 8.2.1 Assembly rules . ^ 8.2.2 Incidence functions and tramps . •< . 8.2.3 The dynamics of island assembly 8.2.4 Checkerboard distributions 8.2.5 Combination and compatibility—assembly rules for cuckoo-doves 8.2.6 Criticisms,'null'models, and responses 8.2.7 Other studies of assembly structure ' Nestedness . • Successional island ecology: first elements . Krakatau—succession, dispersal structure, and hierarchies , ' . . 8.5.1 Background , ., 8.5.2 Community succession ' 8.5.3 A dispersal-structured model of island recolonization 8.5.4 Colonization and turnover—the dynamics of species lists 8.5.5 The balance between stochasticism and determinism '.. . Disturbed island ecology revisited ' A general critique of island ecology theory 8.7.1 Scale and the dynamics of island biotas—Haila's critique 8.7.2 Concluding remarks . Summary ' "

144 ^^ 145 ^^ 147 148 149 151 155 161 165

7.3

7.4

8.3 8.4 8.5

! : 8.6 '8.7

p.8

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115 116 118 118 122 122 123 123 125 125 127 128 129 131 131 133 133 133 134 136 137 142

. - , 166

' . , '. . v

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168 170 .173 178 180 185 187 189 189

x

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Contents

9

Island theory and conservation

9.1 9.2

Habitats as islands Minimum viable populations and minimum viable areas . 9.2.1 How many individuals are needed? . : , 9.2.2 Minimum viable populations and disturbance 9.2.3 How big an area? • ••• , 9.2.4 Applications of incidence functions ••• •^•- s \ • - • -. Metapopulation dynamics •»•'••' -• 9.3.1 The core-sink model variant 9.3.2 Deterministic explanations of extinctions within metapopulations • '.'• Reserve configuration—the'single large or several small'debate ' , . ' .: 9.4.1 Dealing with the leftovers . 9.4.2 The answer depends, in part, on the type of organism • . Physical changes consequent upon fragmentation ' Relaxation and turnover—the evidence • • . . u Succession in fragmented landscapes . . " v '. The implications of nestedness • ••.."..•*" Edge effects • • Landscape effects, isolation, and corridors '. . • 9.10.1 The benefits of wildlife corridors . '.. . • 9.10.2 The benefits of isolation 9.10.3 Reserve systems in the landscape 9.10.4 Species that f don't stay put .. Does conservation biology need island theory? • 9.11.1 A non-equilibrium world? 9.11.2 Ecological hierarchies and fragmented landscapes 9.11.3 Climate change and reserve systems 9.11.4 Concluding remarks ., ; , Summary ' ' .

192 194 194 195 197 197 199 201 203 204 205 207 207 209 212 212 214 216 216 218 220 221 221 221 223 225 225 226

The human impact on island ecosystems— the lighthouse-keeper's cat and other stories

228

• 9.3' • .. . • . 9.4

9.5 9.6 9.7 9.8 9.9 9.10 .

•

9.11

9.12

10

10.1 10.2

10.3 10.4

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Introduction—the scale of loss The agencies of destruction 10.2.1 Predation by humans 10.2.2 Introduced species 10.2.3 Disease 10.2.4 Habitat degradation and loss Trends in the causes of decline . A record of passage—patterns of loss across island taxa 10.4.1 Pacific Ocean birds 10.4.2 Indian Ocean birds ,. 10.4.3 Reptiles ' ' ' '" 10.4.4 Caribbean land mammals 10.4.5 Island snails 10.4.6 Plants in peril

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192

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228 230 230 230 231 232 233 235 235 239 240 241 242 242

4 10.5 10.6

10.7

Contents

xi

How fragile and invasible are island ecosystems? Contemporary problems and solutions 10.6.1 Conservation measures ) 10.6.2 Contemporary problems in the Galapagos 10.6.3 Sustainable development on islands: constraints and remedies Summary

245^ 247 247 250 251 255

Further reading

257

References

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Index

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259 279