Lecture 9-TreesExtinction

Lecture 9-TreesExtinction - AdaptiveRadiation...

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Adaptive Radiation Often happens on islands Many niches are empty Little or no competition Species can evolve to fill an ecological vacuum
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Evolution of Darwin’s Finches
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Anolis radiations in Western Cuba
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Evolutionary (Phylogenetic) Trees Phylogeny = Evolutionary history of a group of organisms Pattern of events that happen as a group diversifies Sequence of lineages (what appeared when)
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Evolutionary Trees A way to establish the relationships between organisms What characters do they share? How closely related are they? When did major evolutionary events happen?
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Evolutionary Trees Oldest organisms on the bottom (base of the trunk) Younger species at the top
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Evolutionary Trees Branches may be linear (no evolutionary change) Branches may fork (evolutionary divergence)
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Evolutionary Trees Groups that are more closely related should share more traits Groups that are less related should share less traits
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Creating Evolutionary Trees Traits used must be independent (change in one character cannot change another character) Characters must be homologous (similarity in traits is due to a common ancestor)
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Homology Similarity in traits is due to a common ancestor Shared traits derived from a common ancestor = synapomorphies Evolutionary relationships are revealed by shared derived traits (synapomorphies)
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Homology A structure present in an ancestor species is retained in a descendent, but the structure may be highly modified
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Bone homologies in vertebrate forelimbs Bones can fuse or be lost Bone shape and size can be modified
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Evolutionary Trees Synapomorphies identify evolutionary branch points Synapomorphies are nested (each branching event adds more shared derived traits)
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Evolutionary Trees Cladogram = phylogenetic tree created by clustering synapomorphies http://www.ncseweb.org/resources/rncse_content/vol21/21_56dinobirds.jpg
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Evolutionary Trees More than one tree may be possible How do you determine the best tree?
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Evolutionary Trees Problems can arise in making a tree Homoplasy = similarity of characters NOT due to a shared common ancestor
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Convergent Evolution Convergent organisms may look very similar or have similar structures.
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Convergent Evolution Convergent organisms may play similar roles in the environment, but they have: Different evolutionary histories Different ancestors Different DNA
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This note was uploaded on 08/30/2008 for the course BIOS 230 taught by Professor Gibbons during the Spring '08 term at Ill. Chicago.

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Lecture 9-TreesExtinction - AdaptiveRadiation...

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