EOSC 326 Lecture Notes - Norse Funeral, Pleistocene, Dynamic Equilibrium

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Published on 19 Apr 2013
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Lesson 18. Biogeographic Principles
Learning Objectives
By the end of this Lesson (18), you should be able to:
1. Describe what factors control speciation events;
Allopatric speciation speciation that occurs when populations become physically
separated (geographic isolation then genetic isolation)
Punctuated (quantum) equilibrium small isolated population rapidly diverges into
new species, no intermediate fossils
Hybrid zones (dynamic equilibrium) expand if interbreeding becomes more frequent
(high gene flow)
Sympatric speciation difference in breeding time prevents interbreeding
2.Compare and contrast cosmopolitan and endemic species;
Cosmopolitan - restricted to certain habitats but found worldwide in these habitats e.g. Bay
Mussel in temperate waters
Endemic - small, restricted ranges e.g. Galapagos finches, different species on each island
3. Discuss why there is a species latitudinal diversity gradient;
Species diversity is highest in the tropics and declines toward the poles
Pleistocene epoch: 1.6 Ma to 12,000 ya froze high latitude areas
Higher latitudes have been more recently affected by processes such as glaciation and
have not had time to reach equilibrium since these historical events ended.
4. Compare and contrast speciation events related to dispersalist and vicariance
biogeography.
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Dispersalist: animals spread out from a centre of origin, crossing preexisting barriers
that they would not readily recross and that would cut them off from the original group
Sweepstake Routes rare chance events, esp. for isolated islands
Vicariant: species that is present over a wide area becomes fragmented (vicariated) as a
barrier develops, as occurred through the process of continental drift
Both: no gene flow
Outline
1. Species Distribution
Cosmopolitan - restricted to certain habitats but found worldwide in these habitats e.g. Bay
Mussel in temperate waters
Endemic - small, restricted ranges e.g. Galapagos finches, different species on each island
2. Latitudinal Diversity Gradient
Species diversity is highest in the tropics and declines toward the poles
Pleistocene epoch: 1.6 Ma to 12,000 ya froze high latitude areas
3. Dispersalist Biogeography
Allopatric speciation speciation that occurs when populations become physically
separated (geographic isolation then genetic isolation)
a. Mechanisms of Dispersal
Corridors organisms free travel between two regions e.g. Oregon & New York
Filter Bridges - selective passage between two areas thus some organisms can pass
while others cannot, i.e. disrupted by mountains, oceans, or certain climates e.g.
Isthmus of Panama b/w N.A. & S.A., formed 2.5 Ma after Oligocene (34 to 23 Ma) &
Pliocene (5.3 to 2.6 Ma)
“Great American Biotic Interchange” 2.5 Ma across Isthmus of Panama only savanna-
adapted animals e.g. animals moved to SA: skunks, horses, deer & cougar
e.g. animals moved to NA: armadillos, opossums and anteaters
Sweepstake Routes rare chance events, esp. for isolated islands
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