Biogeography is the study of the distribution of
speciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(
biologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
), organisms, and ecosystems in
spaceGeography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of
latitudeIn geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
,
elevationThe elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....
,
isolationAllopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
and habitat
areaIn ecology, a species-area curve is a relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical...
. Knowledge of spatial variation in the numbers and types of organisms is as vital to us today as it was to our early human ancestors, as we adapt to heterogeneous but geographically predictable
environmentsThe natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
. Biogeography is an integrative field of inquiry that unites concepts and information from
ecologyEcology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, evolutionary biology,
geologyGeology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, and
physical geographyPhysical geography is one of the two major subfields of geography. Physical geography is that branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, biosphere and geosphere, as opposed to the cultural or built environment, the...
. Modern biogeographic research combines information and ideas from many fields, from the physiological and ecological constraints on organismal
dispersalBiological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
to geological and climatological phenomena operating at global spatial scales and
evolutionEvolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary time frames.
Introduction
The patterns of species distribution across geographical areas can usually be explained through a combination of historical factors such as:
speciationSpeciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
;
extinctionIn biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
;
continental driftContinental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...
; glaciation, and associated variations in
sea levelMean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, river routes, and habitat; and
river captureStream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream...
; in combination with the geographic constraints of landmass areas and isolation; and the available ecosystem energy supplies.
Over periods of
ecologicalEcology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
changes, biogeography includes the study of plant and animal species in: their past and/or present living
refugium habitat* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
; their interim living sites; and/or their survival locales. As writer David Quammen put it, "...biogeography does more than ask
Which species? and
Where. It also asks
Why? and, what is sometimes more crucial,
Why not?."
Modern biogeography often employs the use of Geographic Information Systems (GIS), to understand the factors affecting organism distribution, and to predict future trends in organism distribution.
Often mathematical models and GIS are employed to solve ecological problems that have a spatial aspect to them.
Biogeography is most keenly observed on the world's islands. These habitats are often much more manageable areas of study because they are more condensed than larger ecosystems on the mainland. Islands are also ideal locations because they allow scientists to look at habitats that new species have only recently colonized and can observe how they disperse throughout the island, the success they achieve in these places, and they can then apply this information to similar mainland habitats. Islands are very diverse in their biomes, ranging from the tropical to arctic climates. This diversity in habitat allows for a wider range of species study in different parts of the world.
One scientist who recognized the importance of these geographic locations was
Charles DarwinCharles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
, who remarked in his journal "The Zoology of Archipelagoes will be well worth examination". Two chapters in
On the Origin of Species were devoted to geographical distribution.
History
The scientific theory of biogeography grows out of the work of
Alexander von HumboldtFriedrich Wilhelm Heinrich Alexander Freiherr von Humboldt was a German naturalist and explorer, and the younger brother of the Prussian minister, philosopher and linguist Wilhelm von Humboldt...
(1769–1859), Hewett Cottrell Watson (1804–1881), Alphonse de Candolle (1806–1893),
Alfred Russel WallaceAlfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
(1823–1913), Philip Lutley Sclater (1829–1913) and other biologists and explorers.
Wallace studied the distribution of flora and fauna in the
Amazon BasinThe Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
and the
Malay ArchipelagoThe Malay Archipelago refers to the archipelago between mainland Southeastern Asia and Australia. The name was derived from the anachronistic concept of a Malay race....
in the mid-19th century. Wallace and Sclater saw biogeography as a source of support for the theory of evolution. Key findings, such as the sharp difference in fauna either side of the
Wallace LineThe Wallace Line separates the ecozones of Asia and Wallacea, a transitional zone between Asia and Australia. West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin is present...
, and the sharp difference that existed between North and South America prior to their relatively recent
faunal interchangeThe Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
, can only be understood in this light. Otherwise, the field of biogeography would be seen as a purely descriptive one.
The publication of
The Theory of Island BiogeographyThe Theory of Island Biogeography is a 1967 book by Edward O. Wilson and Robert MacArthur which laid the foundations for the study of island biogeography. An edition with a new preface by Edward O. Wilson was published in 2001 ....
by
Robert MacArthurRobert Helmer MacArthur was an American ecologist who made a major impact on many areas of community and population ecology....
and E.O. Wilson in 1967 showed that the species richness of an area could be predicted in terms of such factors as habitat area, immigration rate and extinction rate.
This added to the long-standing interest in
island biogeographyIsland biogeography is a field within biogeography that attempts to establish and explain the factors that affect the species richness of natural communities. The theory was developed to explain species richness of actual islands...
. The application of island biogeography theory to
habitat fragmentsHabitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
spurred the development of the fields of
conservation biologyConservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
and
landscape ecologyLandscape ecology is the science of studying and improving relationships between urban development and ecological processes in the environment and particular ecosystems...
.
Classic biogeography has been expanded by the development of molecular systematics, creating a new discipline known as
phylogeographyPhylogeography is the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals. This is accomplished by considering the geographic distribution of individuals in light of the patterns associated with a gene genealogy.This term was...
. This development allowed scientists to test theories about the origin and dispersal of populations, such as
island endemicEndemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
s. For example, while classic biogeographers were able to speculate about the origins of species in the
Hawaiian IslandsThe Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, phylogeography allows them to test theories of relatedness between these populations and putative source populations in
AsiaAsia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Paleobiogeography
Paleobiogeography goes one step further to include paleogeographic data and considerations of
plate tectonicsPlate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
. Using molecular analyses and corroborated by fossils, it has been possible to demonstrate that perching birds evolved first in the region of
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
or the adjacent
AntarcticThe Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
(which at that time lay somewhat further north and had a temperate climate). From there, they spread to the other
GondwanaIn paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n continents and Southeast Asia - the part of
LaurasiaIn paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
then closest to their origin of dispersal – in the late
PaleogeneThe Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
, before achieving a global distribution in the early
NeogeneThe Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
. Not knowing the fact that at the time of dispersal, the Indian Ocean was much narrower than it is today, and that South America was closer to the Antarctic, one would be hard pressed to explain the presence of many "ancient" lineages of perching birds in Africa, as well as the mainly South American distribution of the suboscines.
Paleobiogeography also helps constrain hypotheses on the timing of biogeographic events such as
vicarianceVicariance is a process by which the geographical range of an individual taxon, or a whole biota, is split into discontinuous parts by the formation of a physical barrier to gene flow or dispersal. Vicariance of whole biotas occurs following large-scale geophysical events such as the uplift of a...
and
geodispersalIn biogeography, geodispersal is the erosion of barriers to gene flow and biological dispersal . Geodispersal differs from vicariance as a means of explaining the patterns of distribution among related species...
, and provides unique information on the formation of regional biotas. For example, data from species-level phylogenetic and biogeographic studies tell us that the
AmazonThe Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
ian fish fauna accumulated incrementally over a period of tens of millions of years, principally by means of allopatric speciation, and in an arena extending over most of the area of tropical South America (Albert & Reis 2011). In other words, unlike some of the well-known insular faunas (Galapagos finches, Hawaiian drosophilid flies, African rift lake cichlids), the species-rich Amazonian ichthyofauna is not the result of recent
adaptive radiationIn evolutionary biology, adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different...
s. For
freshwaterFresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
organisms, landscapes are divided naturally into discrete
drainage basinA drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
s by watersheds, episodically isolated and reunited by
erosionErosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
al processes. In regions like the
Amazon BasinThe Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
with an exceptionally low (flat) topographic relief, the many waterways have had a highly reticulated history over geological time. In such a context stream capture is an important factor affecting the evolution and distribution of freshwater organisms. Stream capture occurs when an upstream portion of one river drainage is diverted to the downstream portion of an adjacent basin. This can happen because of
tectonic upliftTectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
(or
subsidenceSubsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...
), natural damming as a result of a
landslideA landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
, or by headward or lateral
erosionErosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
of the watershed between adjacent basins.
Classification
Biogeography is a synthetic science, related to
geographyGeography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...
,
biologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
,
soil scienceSoil science is the study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.Sometimes terms which...
,
geologyGeology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
,
climatologyClimatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
,
ecologyEcology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and
evolutionEvolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
.
Some fundamental concepts in biogeography include:
- evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
– change in genetic composition of a population
- extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
– disappearance of a species
- dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
– movement of populations away from their point of origin, related to migrationBird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
- geodispersal
In biogeography, geodispersal is the erosion of barriers to gene flow and biological dispersal . Geodispersal differs from vicariance as a means of explaining the patterns of distribution among related species...
– the erosion of barriers to bioticBiotic is a living component of a community; for example organisms, such as plants and animals.Biotic may also refer to:*Life, the condition of living organisms,*Biology, the study of life,*Biotic material, which is derived from living organisms,...
dispersal and gene flow, that permit range expansion and the merging of previously isolated biotaBiota may refer to:* Biota , the plant and animal life of a region* Biota , a superdomain in taxonomy* Biota , an evergreen coniferous tree, Platycladus orientalis* Biota , an avant-prog band from Colorado, USA...
s
- range
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
and distribution
- endemic areas
- vicariance
Vicariance is a process by which the geographical range of an individual taxon, or a whole biota, is split into discontinuous parts by the formation of a physical barrier to gene flow or dispersal. Vicariance of whole biotas occurs following large-scale geophysical events such as the uplift of a...
– the formation of barriers to biotic dispersal and gene flow, that tend to subdivide species and biotas, leading to speciation and extinction
Further reading
- Albert, J. S., & R. E. Reis (2011). Historical Biogeography of Neotropical Freshwater Fishes. University of California Press, Berkeley. 424 pp. http://www.ucpress.edu/book.php?isbn=9780520268685
- Albert, J.S., & W.G.R. Crampton (2010). The geography and ecology of diversification in Neotropical freshwaters. Nature Education 1(10): 3.
External links
Major journals