History of Biogeography

Biogeography can be traced (like most every other discipline) to Aristotle….

In the 3rd Century B.C., he suggested a view of a dynamic earth to help explain variation in life over space and time.

The development of biogeography is linked to the development of evolutionary biology and ecology. The growth of these disciplines, in turn, were linked to the age of European exploration.

Although the Darwinian revolution was very significant to the study of biogeography, many of the major ideas predate Darwin.

Persistent themes in biogeography

1. Classifying geographic regions based on their biotas.

2. Reconstructing the historical development of lineages and biotas, including their origin, spread, and diversification.

3. Explaining the differences in numbers as well as types of species among geographic areas, and along geographic gradients including those of areas, isolation, latitude, elevation, and depth.

4. Explaining geographic variation in the characteristics of individuals and populations of closely related species, including trends in morphology, behavior, and demography.

Early biogeographers, or “naturalists”, collected information about the diversity and distribution of living things.

It was becoming clear that a scheme for classification was necessary.

It was also becoming clear that the diversity of living things could not be explained in a purely Biblical way.

Carolus Linnaeus (1707-1778)

Developed a scheme for the classification of all life.

This system is still in use today.

Linnaeus also had ideas about biogeography.

He thought that all life had originated on the slopes of a “Paradisical Mountain”, where they were adapted to a particular habitat on the slopes of the mountain. They then dispersed to occupy the various habitats of the globe.

He hypothesized a similar spread of organisms following the landing of Noah’s ark.

Ararat

Georges-Louis Leclerc, Comte de Buffon

(1707-1788)

Studied living and fossil mammals, and arrived at conclusions different from those of Linnaeus.

Hypothesized that life originated in a region of northwestern Europe during earlier times, then migrated into the New World and the Southern Hemisphere, changing over time.

“Man is totally a production of heaven; But the animals, in many respects, are creatures of the Earth only. Those of one continent are not found in another; or, if there are a few exceptions, the animals are so changed that they are hardly recognized.”

A comparison of the ideas of Linnaeus and Buffon. Linnaeus believed that organisms spread from Mount Ararat, or another low latitude mountain following the Great Flood.

Buffon thought that life originated in northern Europe and spread southward, and to the New World.

Buffon’s view of the change (degeneration) of life forms with time, and his belief that New World life forms were somehow inferior was one factor that led Thomas Jefferson to commission the Lewis and Clark expedition to survey the western portions of the American continent.

Buffon’s observations led to the first principle of biogeography, known as Buffon’s Law. It states that environmentally similar but isolated regions have distinct assemblages of mammals and birds.

Sir Joseph Banks

Accompanied Captain James Cook on a three-year voyage around the world from 1768 to 1771.

Collected ~3600 plant specimens, including over 1000 previously unknown to science.

Affirmed and generalized Buffon’s Law

Johann Reinhold Forster (1729-1798)

Also circumnavigated the globe with Cook.

Developed one of the first systematic descriptions of the world’s biotic regions.

Also worked to extend Buffon’s Law to plants.

Noted the tendency for plant diversity to decrease from the equator to the poles.

Karl Ludwig Willdenow (1765-1812)

German botanist.

Described floristic provinces of Europe.

Suggested many sites of origin, perhaps mountains that were not inundated in the Great Flood. After the deluge, life spread from these multiple sites.

His student, Alexander von Humboldt (1759-1859) is viewed as the father of phytogeography.

Humboldt concluded that, within regions, plants were distributed in floristic belts ranging up the sides of tropical mountains.

Willdenow

Humboldt

The 19th Century – A Golden Age for Biogeography

200 years ago, biogeographers (although not called that at the time) had made a pretty good start at describing the distribution of organisms on the planet.

They had not done nearly as well in terms of describing the causes of these distributions.

To answers these questions, they needed:

a. A better idea about the age of the Earth.

b. A clearer picture of the dynamic nature of the earth’s surface.

c. A better understanding of the origin and spread of biological diversity.

Help was on the way.

Adolphe Brongniart (1801-1876)

Paleobotanist of the 19th Century who used the fossil record to draw inferences regarding ancient climates.

Found tropical fossils in temperate areas. Concluded that the earth’s surface had been altered by the uplift and erosion of mountains.

Charles Lyell (1797-1875)

Regarded as the father of geology.

Saw evidence of the dynamism of the earth’s surface.

Developed the theory of uniformitarianism, stating that the processes that we see operating today on the earth’s surface have always done so.

Wrote Principles of Geology.

The stage was set for the contribution of four British naturalists.

Charles Darwin

1809-1882

Through a series of events, Darwin sailed as an amateur naturalist on the H.M.S. Beagle in 1831.

For a more detailed history of Darwin’s life, take a look at the linked PowerPoint.

The Beagle circumnavigated the globe on its five year voyage.

The voyage had a tremendous influence on Darwin.

Darwin, in turn, had a tremendous influence on biogeograhy and biology in general.

Darwin explained the spread and eventual isolation of taxa as the result of long-distance dispersal.

His arguments threatened to overturn the “steady state” ideas that were entrenched in biogeography.

One of the leading proponents of these ideas was Louis Agassiz (1807-1873). Agassiz believed that species were unchanging, and so were there distributions.

However, Darwin’s views gained support and eventually won out.

The views of the “dispersalists” were challenged by the “extensionists” of the late 19th Century.

They had to propose a variety of vanished land bridges to account for the observed distributions of terrestrial organisms.

(Note the connection between South America and Africa present in all of these proposed land bridges. That will be significant later)

One of the leaders in the extensionist camp was Joseph Dalton Hooker. Hooker was a great friend of Darwin (actually referred to sometimes as “Darwin’s bulldog” as a result of his ferocious defense of the theory of evolution). He was also a very influential botanist who traveled extensively and collected plants from around the world.

Hooker felt that long-distance dispersal was an insufficient explanation for the distribution of many organisms.

He wrote that the evidence supported…

“the hypothesis that of all being members of a once more continuous extensive flora…that once spread over a larger and more continuous tract of land,…which has been broken up by geological and climatic causes.”

When no evidence of vanished land bridges emerged, the extensionist movement lost momentum.

Still, Hooker’s contributions to biogeography were significant.

You have probably noted the fact that botanists made most of the early contributions to biogeography?

Why do you think that was the case?

The impact of zoologists began to increase as the 19th Century progressed. Darwin was one example.

Philip Lutley Sclater was another.

Sclater was an ornithologist who described over 1000 species of birds. His writings had a major impact on zoogeography.

He proposed a scheme that divided the earth into biogeographic regions. His work provide the basis for the biogeographic regions recognized today.

Sclater’s scheme of terrestrial biogeographic regions.

The most significant figure, however, in the history of zoogeography, and biogeography in general, is….

Alfred Russel Wallace (1823-1913)

Wallace is often considered the father of zoogeography.

Wallace wrote three of the most significant books in the history of the science:

The Malay Archipelago (1869)

The Geographical Distribution of Animals (1876)

Island Life (1880)

The authors of your text list, on page 27, a number of biogeographic principles advocated by Wallace. Read through them.

Many of these ideas remain central to the study of biogeography today.

One of Wallace’s early contributions was the recognition of a distinct break in the faunal compositions between the islands of Bali and Lombok in the East Indies.

This break is known today as Wallace’s Line.

Also, in the 19th Century, other biogeographers contributed some generalized “rules” regarding animal distributions.

Bergmann’s rule states that the size of warm-blooded vertebrates tends to be larger in cooler climates. Why might that be?

Allen’s rule says that the extremities of such species tend to be larger in warmer climates and smaller in cool climates.

Cope’s rule states that the evolution of a group is often accompanied by an increase in size.

However, this increase in size often brings with it an increased susceptibility to extinction.

It’s important to remember that all of these rules are generalizations, and that there are many exceptions.

C.H. Merriam’s “life zones” illustrated the relationship between climate and vegetation.

Life zones can be seen both in relation to elevation…..

….and to latitude.

In the early decades of the 20th Century, paleontologists contributed greatly to our understanding of the origin, dispersal, and ultimate decline of many groups of vertebrates.

Much debate focused on “centers of origin”, the place where a group developed.

Four major developments revolutionized biogeography in the latter part of the 20th Century:

1. The acceptance of plate tectonics.

2. The development of new phylogenetic techniques.

3. New ways of conducting ecological research.

4. Investigations in the factors limiting distributions.

We will talk in detail about each of these in later chapters.

The acceptance of plate tectonics as a mechanism driving continental drift has completely changed the way in which we view distributions today.

Perhaps the most significant event in ecological biogeography was the publication of a monograph on island biogeography by E.O. Wilson and Robert MacArthur. In this seminal work, they proposed theories to explain the number of species found on islands.

The effect of various events on the science of biogeography can be seen by looking at the number of publications in the field in relation to the timing of events.