Island Life

by Alfred Russel Wallace

PART I

THE DISPERSAL OF ORGANISMS; ITS PHENOMENA, LAWS, AND CAUSES

CHAPTER I

INTRODUCTORY

Remarkable Contrasts in the Distribution of Animals—Britain and Japan—Australia and New Zealand—Bali and Lombok—Florida and Bahama Islands—Brazil and Africa—Borneo, Madagascar, and Celebes—Problems in Distribution to be found in every Country—Can be Solved only by the Combination of many distinct lines of inquiry, Biological and Physical—Islands offer the best Subjects for the Study of Distribution—Outline of the Subjects to be discussed in the Present Volume.

CHAPTER II

THE ELEMENTARY FACTS OF DISTRIBUTION.

Importance of Locality as an Essential Character of Species—Areas of Distribution—Extent and Limitations of Specific Areas—Specific Range of Birds—Generic Areas—Separate and Overlapping Areas—The Species of Tits as illustrating Areas of Distribution—The Distribution of the Species of Jays—Discontinuous Generic Areas—Peculiarities of Generic and Family Distribution—General Features of Overlapping and Discontinuous Areas—Restricted Areas of Families—The Distribution of Orders

CHAPTER III

CLASSIFICATION OF THE FACTS OF DISTRIBUTION.—ZOOLOGICAL REGIONS

The Geographical Divisions of the Globe do not Correspond to Zoological Divisions—The Range of British Mammals as Indicating a Zoological Region—Range of East Asian and North African Mammals—The Range of British Birds—Range of East Asian Birds—The Limits of the Palæarctic Region—Characteristic Features of the Palæarctic Region—Definition and Characteristic Groups of the Ethiopian Region—Of the Oriental Region—Of the Australian Region—Of the Nearctic Region—Of the Neotropical Region—Comparison of Zoological Regions with the Geographical Divisions of the Globe

CHAPTER IV

EVOLUTION AS THE KEY TO DISTRIBUTION

Importance of the Doctrine of Evolution—The Origin of New Species—Variation in Animals—The amount of Variation in North American Birds—How New Species Arise from a Variable Species—Definition and Origin of Genera—Cause of the Extinction of Species—The Rise and Decay of Species and Genera—Discontinuous Specific Areas, why Rare—Discontinuity of the Area of Parus Palustris—Discontinuity of Emberiza Schœniclus—The European and Japanese Jays—Supposed examples of Discontinuity among North American Birds—Distribution and Antiquity of Families—Discontinuity a Proof of Antiquity—Concluding remarks

CHAPTER V

THE POWERS OF DISPERSAL OF ANIMALS AND PLANTS

Statement of the General Question of Dispersal—The Ocean as a Barrier to the Dispersal of Mammals—The Dispersal of Birds—The Dispersal of Reptiles—The Dispersal of Insects—The Dispersal of Land Mollusca—Great Antiquity of Land-shells—Causes Favouring the Abundance of Land-shells—The Dispersal of Plants—Special Adaptability of Seeds for Dispersal—Birds as Agents in the Dispersal of Seeds—Ocean Currents as Agents in Plant Dispersal—Dispersal along Mountain Chains—Antiquity of Plants as Effecting their Distribution

CHAPTER VI

GEOGRAPHICAL AND GEOLOGICAL CHANGES: THE PERMANENCE OF CONTINENTS

Changes of Land and Sea, their Nature and Extent—Shore-Deposits and Stratified Rocks—The Movements of Continents—Supposed Oceanic Formations; the Origin of Chalk—Fresh-water and Shore-deposits as Proving the Permanence of Continents—Oceanic Islands as Indications of the Permanence of Continents and Oceans—General Stability of Continents with Constant Change of Form—Effect of Continental Changes on the Distribution of Animals—Changed Distribution Proved by the Extinct Animals of Different Epochs—Summary of Evidence for the General Permanence of Continents and Oceans.

CHAPTER VII

CHANGES OF CLIMATE WHICH HAVE INFLUENCED THE DISPERSAL OF ORGANISMS: THE GLACIAL EPOCH

Proofs of the Recent Occurrence of a Glacial Epoch—Moraines—Travelled Blocks—Glacial Deposits of Scotland: the "Till"—Inferences from the Glacial Phenomena of Scotland—Glacial Phenomena of North America—Effects of the Glacial Epoch on Animal Life—Warm and Cold Periods—Palæontological Evidence of Alternate Cold and Warm Periods—Evidence of Interglacial Warm Periods on the Continent and in North America—Migrations and Extinctions of Organisms Caused by the Glacial Epoch

CHAPTER VIII

THE CAUSES OF GLACIAL EPOCHS

Various Suggested Causes—Astronomical Causes of Changes of Climate—Difference of Temperature Caused by Varying Distances of the Sun—Properties of Air and Water, Snow and Ice, in Relation to Climate—Effects of Snow on Climate—High Land and Great Moisture Essential to the Initiation of a Glacial Epoch—Perpetual Snow nowhere Exists on Lowlands—Conditions Determining the Presence or Absence of Perpetual Snow—Efficiency of Astronomical causes in Producing Glaciation—Action of Meteorological Causes in Intensifying Glaciation—Summary of Causes of Glaciation—Effect of Clouds and Fog in Cutting off the Sun's Heat—South Temperate America as Illustrating the Influence of Astronomical Causes on Climate—Geographical Changes how far a Cause of Glaciation—Land Acting as a Barrier to Ocean-currents—The Theory of Interglacial Periods and their Probable Character—Probable Effect of Winter in aphelion on the Climate of Britain—The Essential Principle of Climatal Change Restated—Probable Date of the Last Glacial Epoch—Changes of the Sea-level Dependent on Glaciation—The Planet Mars as Bearing on the Theory of Excentricity as a Cause of Glacial Epochs

CHAPTER IX

ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE ARCTIC REGIONS

Mr. Croll's Views on Ancient Glacial Epochs—Effects of Denudation in Destroying the Evidence of Remote Glacial Epochs—Rise of Sea-level Connected with Glacial Epochs a Cause of Further Denudation—What Evidence of Early Glacial Epochs may be Expected—Evidences of Ice-action During the Tertiary Period—The Weight of the Negative Evidence—Temperate Climates in the Arctic Regions—The Miocene Arctic Flora—Mild Arctic Climates of the Cretaceous Period—Stratigraphical Evidence of Long-continued Mild Arctic Conditions—The Causes of Mild Arctic Climates—Geographical Conditions Favouring Mild Northern Climates in Tertiary Times—The Indian Ocean as a Source of Heat in Tertiary Times—Condition of North America During the Tertiary Period—Effect of High Excentricity on Warm Polar Climates—Evidences as to Climate in the Secondary and Palæozoic Epochs—Warm Arctic Climates in Early Secondary and Palæozoic Times—Conclusions as to the Climates of Secondary and Tertiary Periods—General View of Geological Climates as Dependent on the Physical Features of the Earth's Surface—Estimate of the Comparative Effects of Geographical and Physical Causes in Producing Changes of Climate.

CHAPTER X

THE EARTH'S AGE, AND THE RATE OF DEVELOPMENT OF ANIMALS AND PLANTS

Various Estimates of Geological Time—Denudation and Deposition of Strata as a Measure of Time—How to Estimate the Thickness of the Sedimentary Rocks—How to Estimate the Average Rate of Deposition of the Sedimentary Rocks—The Rate of Geological Change Probably Greater in very Remote Times—Value of the Preceding Estimate of Geological Time—Organic Modification Dependent on Change of Conditions—Geographical Mutations as a Motive Power in Bringing about Organic Changes—Climatal Revolutions as an Agent in Producing Organic Changes—Present Condition of the Earth One of Exceptional Stability as Regards Climate—Date of Last Glacial Epoch and its Bearing on the Measurement of Geological Time—Concluding Remarks

PART II

INSULAR FAUNAS AND FLORAS

CHAPTER XI

THE CLASSIFICATION OF ISLANDS

Importance of Islands in the Study of the Distribution of Organisms—Classification of Islands with Reference to Distribution—Continental Islands—Oceanic Islands

CHAPTER XII

OCEANIC ISLANDS:—THE AZORES AND BERMUDA

The Azores, or Western Islands

Position and Physical Features—Chief Zoological Features of the Azores—Birds—Origin of the Azorean Bird-fauna—Insects of the Azores—Land-shells of the Azores—The Flora of the Azores—The Dispersal of Seeds—Birds as seed-carriers—Facilities for Dispersal of Azorean Plants—Important Deduction from the Peculiarities of the Azorean Fauna and Flora

Bermuda

Position and Physical Features—The Red Clay of Bermuda—Zoology of Bermuda—Birds of Bermuda—Comparison of the Bird-faunas of Bermuda and the Azores—Insects of Bermuda—Land Mollusca—Flora of Bermuda—Concluding Remarks on the Azores and Bermuda

CHAPTER XIII

THE GALAPAGOS ISLANDS

Position and Physical Features—Absence of Indigenous Mammalia and Amphibia—Reptiles—Birds—Insects and Land-shells—The Keeling Islands as Illustrating the Manner in which Oceanic Islands are Peopled—Flora of the Galapagos—Origin of the Flora of the Galapagos—Concluding remarks

CHAPTER XIV

ST. HELENA

Position and Physical Features of St. Helena—Change Effected by European Occupation—The Insects of St. Helena—Coleoptera—Peculiarities and Origin of the Coleoptera of St. Helena—Land-shells of St. Helena—Absence of Fresh-water Organisms—Native Vegetation of St. Helena—The Relations of the St. Helena Compositæ—Concluding Remarks on St. Helena

CHAPTER XV

THE SANDWICH ISLANDS

Position and Physical Features—Zoology of the Sandwich Islands—Birds—Reptiles—Land-shells—Insects—Vegetation of the Sandwich Islands—Peculiar Features of the Hawaiian Flora—Antiquity of the Hawaiian Fauna and Flora—Concluding Observations on the Fauna and Flora of the Sandwich Islands—General Remarks on Oceanic Islands

CHAPTER XVI

CONTINENTAL ISLANDS OF RECENT ORIGIN: GREAT BRITAIN

Characteristic Features of Recent Continental Islands—Recent Physical Changes of the British Isles—Proofs of Former Elevation—Submerged Forests—Buried River Channels—Time of Last Union with the Continent—Why Britain is Poor in Species—Peculiar British Birds—-Fresh-water Fishes—Cause of Great Speciality in Fishes—Peculiar British Insects—Lepidoptera Confined to the British Isles—Peculiarities of the Isle of Man Lepidoptera—Coleoptera Confined to the British Isles—Trichoptera Peculiar to the British Isles—Land and Fresh-water Shells—Peculiarities of the British Flora—Peculiarities of the Irish Flora—Peculiar British Mosses and Hepaticæ—Concluding Remarks on the Peculiarities of the British Fauna and Flora

CHAPTER XVII

BORNEO AND JAVA

Position and Physical Features of Borneo—Zoological Features of Borneo: Mammalia—Birds—The Affinities of the Borneo Fauna—Java, its Position and Physical Features—General Character of the Fauna of Java—Differences Between the Fauna of Java and that of the other Malay Islands—Special Relations of the Javan Fauna to that of the Asiatic Continent—Past Geographical Changes of Java and Borneo—The Philippine Islands—Concluding Remarks on the Malay Islands

CHAPTER XVIII

JAPAN AND FORMOSA

Japan, its Position and Physical Features—Zoological Features of Japan—Mammalia—Birds—Birds Common to Great Britain and Japan—Birds Peculiar to Japan—Japan Birds Recurring in Distant Areas—Formosa—Physical Features of Formosa—Animal Life of Formosa—Mammalia—Land Birds Peculiar to Formosa—Formosan Birds Recurring in India or Malaya—Comparison of Faunas of Hainan, Formosa, and Japan—General Remarks on Recent Continental Islands

CHAPTER XIX

ANCIENT CONTINENTAL ISLANDS: THE MADAGASCAR GROUP

Remarks on Ancient Continental Islands—Physical Features of Madagascar—Biological Features of Madagascar—Mammalia—Reptiles—Relation of Madagascar to Africa—Early History of Africa and Madagascar—Anomalies of Distribution and how to Explain Them—The Birds of Madagascar as Indicating a Supposed Lemurian Continent—Submerged Islands Between Madagascar and India—Concluding Remarks on "Lemuria"—The Mascarene Islands—The Comoro Islands—The Seychelles Archipelago—Birds of the Seychelles—Reptiles and Amphibia—Fresh-water Fishes—Land Shells—Mauritius, Bourbon, and Rodriguez—Birds—Extinct Birds and their Probable Origin—Reptiles—Flora of Madagascar and the Mascarene Islands—Curious Relations of Mascarene Plants—Endemic Genera of Mauritius and Seychelles—Fragmentary Character of the Mascarene Flora—Flora of Madagascar Allied to that of South Africa—Preponderance of Ferns in the Mascarene Flora—Concluding Remarks on the Madagascar Group

CHAPTER XX

ANOMALOUS ISLANDS: CELEBES

Anomalous Relations of Celebes—Physical Features of the Island—Zoological Character of the Islands Around Celebes—The Malayan and Australian Banks—Zoology of Celebes: Mammalia—Probable Derivation of the Mammals of Celebes—Birds of Celebes—Bird-types Peculiar to Celebes—Celebes not Strictly a Continental Island—Peculiarities of the Insects of Celebes—Himalayan Types of Birds and Butterflies in Celebes—Peculiarities of Shape and Colour of Celebesian Butterflies—Concluding Remarks—Appendix on the Birds of Celebes

CHAPTER XXI

ANOMALOUS ISLANDS: NEW ZEALAND

Position and Physical Features of New Zealand—Zoological Character of New Zealand—Mammalia—Wingless Birds Living and Extinct—Recent Existence of the Moa—Past Changes of New Zealand deduced from its Wingless Birds—Birds and Reptiles of New Zealand—Conclusions from the Peculiarities of the New Zealand Fauna

CHAPTER XXII

THE FLORA OF NEW ZEALAND: ITS AFFINITIES AND PROBABLE ORIGIN

Relations of the New Zealand Flora to that of Australia—General Features of the Australian Flora—The Floras of South-eastern and South-western Australia—Geological Explanation of the Differences of these Two Floras—The Origin of the Australian Element in the New Zealand Flora—Tropical Character of the New Zealand Flora Explained—Species Common to New Zealand and Australia mostly Temperate Forms—Why Easily Dispersed Plants have often Restricted Ranges—Summary and Conclusion on the New Zealand Flora

CHAPTER XXIII

ON THE ARCTIC ELEMENT IN SOUTH TEMPERATE FLORAS

European Species and Genera of Plants in the Southern Hemisphere—Aggressive Power of the Scandinavian Flora—Means by which Plants have Migrated from North to South—Newly Moved Soil as Affording Temporary Stations to Migrating Plants—Elevation and Depression of the Snow-line as Aiding the Migration of Plants—Changes of Climate Favourable to Migration—The Migration from North to South has been Long going on—Geological Changes as Aiding Migration—Proofs of Migration by way of the Andes—Proofs of Migration by way of the Himalayas and Southern Asia—Proofs of Migration by way of the African Highlands—Supposed Connection of South Africa and Australia—The Endemic Genera of Plants in New Zealand—The Absence of Southern Types from the Northern Hemisphere—Concluding Remarks on the New Zealand and South Temperate Floras

CHAPTER XXIV

SUMMARY AND CONCLUSION

The Present Volume is the Development and Application of a Theory—Statement of the Biological and Physical Causes of Dispersal—Investigation of the Facts of Dispersal—Of the Means of Dispersal—Of Geographical Changes Affecting Dispersal—Of Climatal Changes Affecting Dispersal—The Glacial Epoch and its Causes—Alleged Ancient Glacial Epochs—Warm Polar Climates and their Causes—Conclusions as to Geological Climates—How Far Different from those of Mr. Croll—Supposed Limitations of Geological Time—Time Amply Sufficient both for Geological and Biological Development—Insular Faunas and Floras—The North Atlantic Islands—The Galapagos—St. Helena and the Sandwich Islands—Great Britain as a Recent Continental Island—Borneo and Java—Japan and Formosa—Madagascar as an Ancient Continental Island—Celebes and New Zealand as Anomalous Islands—The Flora of New Zealand and its Origin—The European Element in the South Temperate Floras—Concluding Remarks