Biogeography

Study of distribution of organisms

Biogeography

• Comparative observational science

• Experiments – limited utility

• Multiple scales

• Comparative has uses, though

• Synthetic science

Subjects Used in Biogeography

• Anatomy• Physiology• Taxonomy• Developmental• Evolution• Geology• Geography• Ecology• Climatology, Paleontology……

Relevance of Biogeography

• What enables a species to live where it doe, and what prevents it from colonizing other areas?

• What are a species closest relatives and where can they be found? Where did its ancestors live?

• How have historical events shaped a species’ distribution?

Overarching question: What shapes global patterns of biodiversity?

The Importance of Time

• Historical biogeography

• Ecological biogeography

• Paleoecology

“While the process of science owes much to admirable human traits……..it is also

retarded by characteristics such as prejudice, jealousy, short-sightedness, and

stupidity.”

History of Biogeography

• Roots from questions that developed during the “Age of Exploration”

• Shares common lineage with ecology

• Early questions– From where did life come?– How did it diversify across the planet?

Persistent Themes in Biogeography

• Classifying geographic regions based on their biota

• Reconstructing historical development or lineages and biota, including their origin, spread, and diversification

• Explaining differences in numbers and types of species among geographic areas, and along geographic gradients

• Explaining geographic variation in characteristics of individuals and populations of closely related species

Age of Exploration

• 250 yr ago, only 1% of species known today identified

• Mission – reveal mysteries of creation by learning of the diversity of life

• Prevailing view – stasis

• With increasing identification of species, was a clear need for organization

Carolus Linneaus (1707 – 1778)

• Understanding organization would lead to knowing Creator’s plan

• Took static view of Earth• Explain origin and spread of

life• Challenge was to explain

diversity and distribution

Carolus Linneaus (1707 – 1778)

• How could life have spread from Paradise then landing spot of the Ark

• Linnaeus – “Paradisical Mountain” – a mountain island life along the slopes, perfectly adapted for biotic and abiotic conditions at their “station”

• Based on known conditions of tropical mountains

• Later formation of land allowed spread

Comte de Buffon (1707 – 1788)

• Contemporary of Linaeus• Disagreed with his view of

spread of life (living and fossil specimens)

• Places with same climate had different species

• Inhospitable environment around Mount Ararat

• Proposed origin in northern Europe

• Buffon’s hypothesis – climate was cooler at time allowing species to move to new areas and change

• Key points – climate and species were dynamic (central to modern biogeographic theory and precursor to development of evolutionary theory)

Comte de Buffon (1707 – 1788)

• Buffon’s Law – Environmentally similar but separated regions have different species of birds and mammals

• Considered first principle of biogeography

• Later studies by Joseph Banks and Johann Forster found Buffon’s Law applied to plants

Phytogeography

• End of 18th century – natural theology still primary biological theory

• Willdenow (1765-1812) and Humboldt (1769-1859) – phytogeography – geographic distribution of plants

• Studies of plant distribution on Andes mountain (5,600 m elevation

Mt. Chimbaruzo

Phytogeography

• Identified floristic belts from tropical to arctic

• Observed plant communities closely associated with local climate

• Hints at competition (Candolle) Mt. Chimbaruzo

Biogeography of 19th Century

• First three themes established– Classifying geographic regions based on their

biota– Reconstructing historical development or

lineages and biota, including their origin, spread, and diversification

– Explaining differences in numbers and types of species among geographic areas, and along geographic gradients

Biogeography of 19th Century

• Buffon’s Law– Early biogeographers tested– Classify regions based on biota (theme 1)– Reconstructing origin and spread of life

(theme 2)– Changes along gradients (theme 3)– Established approachs still used

• Perception of static earth and life to dynamic

Limitations

• Number of local species increased with area

• Number of species decreased from equator

• Needed to move to next step (rigorous testing) but first needed

WHY??????

Needs for Better Understanding

• Better estimate of age of Earth (natural theology and 6,000 yr)

• Understanding of dynamic nature of continents and oceans

• Understanding of spread and diversification – dispersal, vicariance, extinction, evolution)

Early Advances of 19th Century

• Borngniart – father of paleobotany• Lyell – father of geology• Both used fossil record to conclude climate

changes over time (life forms of tropical climates in northern Europe

• Lyell – changes in sea level and the lifting and erosion of mountains; extinction

• New species arose through new creations after extinctions; new species created for new climate

Early Advances of 19th Century

• Lyell proposed uniformitarianism

• Also, realization that processes occur slowly (gradualism)

• Time needed for geological processes + continual replacement of biota = Earth much older than 6,000 years

Four British Scientists

• Charles Darwin, Joseph Hooker, Philip Sclater, Alfred Russell Wallace

• Naturalists, traveling the world and discovering diversity

• Shared their observations, building a broader image of life

• Did not agree on all points

Darwin

• Origin of Species – contribution is obvious

• Proposed ideas on dispersal of life (countering Agassiz’s view of point near creation)

• The “dispersalist” view made dispersal dynamic

• Disagreement then moved to mechanisms of dispersal (dispersalists vs. extensionists)

Extensionists &Land Bridges

Further Contributions

• Hooker – study of southern hemisphere plant distributions lead to development of vicariance biogeography

• Sclater – used distribution of passerine (perching) birds to develop a system of six biogeographic regions still used today

• Also developed zones based on marine mammals (Fig. 2.8)

Wallace

• Greatest contributions to biogeography (father of zoogeography)

• Expanded view provided by Sclater’s zones

• Established many of the basic principles of biogeography (see Box 2.1)

• Observed a distinct change in fauna of Southeast Asia and Australasia (Wallace Line)

Other 19th Century Contributions

• Bergmann’s rule – homeotherms, body size, and surface-to-volume ratio from poles

• Allen’s rule – limbs of birds and mammals become shorter and stouter as move from equator.

• Cope’s rule – groups tend to increase in size during their evolution

• Limitation of generalities but open new thoughts

Other 19th Century Contributions

• Merriam’s life zones

• Study of elevational changes – found vegetation types and species composition are similar to longitudinal patterns

• Confirmed Humboldt’s work

Twentieth Century

• Burdgeoning info from paleontology

• Origin, dispersal, radiation, and decline of terrestrial vertebrates

• Development of phylogenies– New groups rise– Increase in number of species– Radiate to fill niches and expand range

• Still – question of how dispersed

Twentieth Century

• Relationships between geological and ecological properties of environment

• Patterns of morphological variation

• Coincided with Modern Synthesis

• Linking lead to formulation of biological species concept (Ernst Mayr)

• Also identified allopatric speciation

Continental Drift

• Earth’s crust believed fixed until 1960s

• Continental drift 1st proposed 1858

• Resurfaced by Wegener and Taylor using geological and ecological evidence

• Criticized and denied until evidence became overwhelming

• Changed dispersal from land bridges to movements of continents

New Phylogenetic Methods

• Continental drift lead to study of disjunctions

• Vicariance biogeography

• Examination and revision of phylogenies

Further Aids

• Computers

• Geographic information systems

• Geostatistics