Evol2 - Effects of Natural Selection on Populations No...

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Effects of Natural Selection on Populations No Selection – Variability tends to increase (why?) Stabilizing Selection – Extreme traits are at a disadvantage Directional Selection – Usually due to environmental change
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A classic study of natural selection Both moths shown above belong to the same species ( Biston betularia – the Peppered Moth). Frequencies of the dark form on the right became very abundant near London and other industrial cities in England during the Industrial Revolution. This trend reversed more recently as England used better pollution control. What form of selection (see previous slide) was probably involved from 1960-1980?
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Selection for body size in English Sparrows Assuming that body size is heritable, what form of selection probably occurred among male sparrows during the ice storm? Total length (mm) 170 165 160 155 150 32 30 28 26 24 22 SURVIVE? no yes Survival of male sparrows following an ice storm in Rhode Island
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Two special cases of Natural Selection Artificial Selection : Humans produce evolutionary change by encouraging reproduction of only preferred phenotypes. Sexual Selection : Choice of mates by one sex exerts selection on the behavior, appearance or other attributes of the other sex. In species where the female typically contributes more to offspring, it’s the females who choose …
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Anasazi Cliff dwelling
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Artificial Selection in Corn Corn has evolved from a grass ( Teosinte ) through selective breeding by native Americans beginning 7,000 years ago. And continues to evolve …
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Sexual Selection in Bullfrogs Males call, females listen … Females swim toward deeper, louder calls. A few big males do most of the mating … Why might choosing a deep voice be adaptive for a female? What selection pressure does this place on the evolution of males? Is there any hope for small males with high voices? http://animaldiversity.ummz.umich.edu/site/accounts/sounds/Rana_catesbeiana.html
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Sexual Dimorphism in Elephant Seals Males typically 1800-2700 kg; have thick necks, pronounced proboscis Females typically about 900 kg, without thickened necks or proboscis Breeding is rookeries on islands off the California coast
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Mating Systems shape the intensity of sexual selection on the two sexes • Monogamy : males and females each have a single mate
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Evol2 - Effects of Natural Selection on Populations No...

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