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Diversification and RegionalizationMODULE 10: DIVERSIFICATION AND REGIONALIZATIONUNIT 2: HISTORICAL BIOGEOGRAPHY

Objectives

At the end of this series of lectures you should be able to: Define terms.

Discuss the fundamental geographic patterns.

Discuss provincialism.

Describe the Great American Biotic Interchange.

Discuss convergent evolution.

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Fundamental Geographic Patterns

Cosmopolitan Endemic

Use of the term is scale dependent Autochthonous endemics Allochthonous endemics

Taxonomic relicts Biogeographic relicts

Provincialism

Disjunction

Provincialism

Buffon’s Law

Hierarchical Realms/Regions Subregions Provinces Districts

Somewhat problematic at the lower hierarchical levels.

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Provincialism

Biogeographical Regions Nearctic Palearctic Neotropical Ethiopian Oriental Australian

Holarctic

Note where the boundaries are not consistent with the continental boundaries.

Provincialism

Biogeographical lines Example: Boundary between the Oriental and Australian regions.

Different lines represent differences in the dispersal of different groups, geographic limits, or ecological .

Wallace’s line – Birds

Huxley’s line – Asian continental plate

Murray’s line – Faunal break

Muller’s line – Arid region/Mammals

Sclater’s line – Mammals

Weber’s line – Freshwater Fish

Lydekker’s line – Australian continental plate

Only slight modifications of Wallace’s line.

Edges of the tectonic plates. Dispersal during glaciation.

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Great American Biotic Interchange

While Pangea existed different terrestrial species had access to all of the land masses. Formidable ecological and physiological barriers kept

complete mixing from occurring.

Mammals have their first modest radiation at 220 mya. Pangea is nearly whole and early mammals occupy

the whole of the super-continent.

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Great American Biotic Interchange

160 mya North America separates from South America. North America has regular contact with Eurasia from the east and the

west Biota moves relatively freely

140 mya South America separates from Africa. South America is now isolated. Its biota evolves in isolation.

Great American Biotic Interchange

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Great American Biotic Interchange

Mammals are small bodied and a small relatively insignificant component of the biota.

65 mya an asteroid takes out the dinosaurs. Ecological vacancies allow the mammals to diversify. South America is an island continent its biota

continues to evolve in isolation. Splendid isolation

Great American Biotic Interchange

South American mammals evolve into diverse forms Monotremes – Platypus

Marsupials – Incredible diversity rivaling Australia Opossums

Sabertooth marsupial cats

Placentals – Strange forms “Ungulates”

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Great American Biotic Interchange

10-15 mya North and south America approach each other causing the uplift of Central America. Early this is an archipelago of stepping stones –

sweepstake dispersal. Edentates – Ancestors of sloths, armadillos, anteaters Primates – Ancestors of new world monkeys Rodents – Ancestors of large rodents

Porcupines, capybaras, pacas, agoutis, guinea pigs etc.

These groups diversified in South America’s isolation. Developed a large and diverse mammalian fauna.

Great American Biotic Interchange

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Great American Biotic Interchange

3.5 mya South America’s isolation ends suddenly with the completion of Central America. A barrier for oceanic organisms A filter for terrestrial and freshwater forms Habitat in Central America was heavily influenced by glacial cycles.

Influenced what could move and when they could move.

Great American Biotic Interchange

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Great American Biotic Interchange

The biotas of North and South America mix – albeit not smoothly or completely.

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Great American Biotic Interchange

Mammalian diversity at the generic level North American unchanged

Addition of a few South American forms

No major extinctions

South American greatly increased Addition of many North American forms

Major extinction spasm with loss of South American endemics

Great American Biotic Interchange

Half of all current South American mammal species are descendants of North American forms.

Only 10% of North American mammal species are descendants of South American forms.

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Great American Biotic Interchange

Advantages of northern species Better migrators Better survivors and speciators Better competitors Better able to cope with predation, parasitism, and

pathogens North America is larger than South America North America had frequent contact with the

even larger Eurasia.

Great American Biotic Interchange

Other vertebrates Herpetofauna and avifauna assembled gradually – no

clear distinction between northern and southern forms Birds show a balanced exchange between North and South

America. Neotropical migrants are almost all descended from South

American forms North America received more reptiles and amphibians than it

gave South America. Fish faunas have had very limited mixing

Active area of research Primarily South American forms moving north.

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Convergence

In similar environments, unrelated or distantly related forms will evolve toward similar phenotypes. Behavior and morphology

Tucos

Tympas

Parallelism

Convergence of communities

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