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Lecture 8: Phenotypic Responses to Temperature
Reading: Economy of Nature, pp. 208-230.
Higher Level Systematics and Macro-evolutionary
Phenomena
Higher level systematics are groupings
of species based on phenotypes (similarities and differences, shared characteristics)
that are hoped to reflect evolutionary descent relationships:
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Species
grouped in a Genus |
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Genera grouped
in a Family |
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Families
grouped in an Order |
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Orders grouped
in a Class |
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Classes
grouped in a Phylum |
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Phyla grouped
in a Kingdom |
Long-term evolutionary change at higher
level systematic categories is termed macro-evolution (geological time
scale).
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Speciation:
one species subdividing (diverging) to two species |
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Phyletic
evolution: change within a single line of descent |
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Extinction:
termination of a given line of descent |
In geological time, there have been six
major periods of mass extinction:
500 million years ago
Cambrian, extinction of 50% of animal families
345 million years ago Devonian,
extinction of 30% of animal families
230 million years ago Permian,
extinction of 50% of animal families
extinction
of 95% of marine species
180 million years ago Triassic,
extinction of 35% of animal families
65 million years ago Cretaceous,
extinction of dinosaurs, 70% of animal species
10,000 years ago Pleistocene,
extinction of large mammals and birds
Causes of mass extinctions
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major
events in continental drift, mountain building periods,
volcanic activity |
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sea level
lowering, exposing continental shelves |
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asteroid/comet
impacts (100 million year intervals) |
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human
activity, explosions, habitat destruction, overutilization,
overhunting |
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long term
cycles in earth orbit and sunlight intensity |
Biological factors influencing likelihood
of extinction:
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rarity |
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dispersal
ability |
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degree
of specialization |
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population
density variability |
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trophic
status |
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longevity |
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intrinsic
rate of population growth |
Responses to Temperature
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Most organisms
cannot tolerate temperatures greater than 45°C
because protein denaturation begins at this and higher temperatures.
Exceptions are photosynthetic cyanobacteria which may tolerate
75°C, and some thermophilic bacteria that exist in hot springs at
temperatures close to 100°C. |
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Cold tolerance
is limited by ice crystal formation. Solutes in water
depress the freezing point and inhibit ice formation. Glycerol and
glycoproteins may be produced specifically to depress the freezing
point of body fluids. |
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Metabolic
rate responds to temperature, as temperature increases,
chemical reaction rates increase. Typically, there is a 2x - 4x rate
change for each 10°C change. Temperature can influence protein
conformation so functional conformation changes with temperature. |
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