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13.16 to 13.18.  Struggle for Existence & Survival of the fittest ◦ Because there are limiting resources (food, shelter, competition, predation, etc…)

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Presentation on theme: "13.16 to 13.18.  Struggle for Existence & Survival of the fittest ◦ Because there are limiting resources (food, shelter, competition, predation, etc…)"— Presentation transcript:

1 13.16 to 13.18

2  Struggle for Existence & Survival of the fittest ◦ Because there are limiting resources (food, shelter, competition, predation, etc…) organisms struggle to survive. ◦ Organisms that are best suited for their environment will have a better chance to survive allowing them to reproduce and pass on their traits that made them better suited for survival.

3  Fitness ◦ The contribution an individual makes to the gene pool of the next generation, relative to the contribution of other individuals in the population ◦ Those with higher fitness will make a greater contribution to the gene pool; those with lower fitness may not contribute to the gene pool at all

4 Stabilizing SelectionExample  Type of natural selection that favors intermediate variants by acting against extreme population  Human birth weight is usually in the range of 6.5lbs to 9lbs. Smaller babies have increased health risks. Larger babies lead to health risks for the mother.

5 Directional SelectionExample  Type of natural selection that acts against the relatively rare individuals at one end of the phenotype range.  Pesticide resistance in insects.

6 Disruptive SelectionExample  Type of natural selection that favors extremes over intermediate phenotypes  Coloration of African Swallowtail – extremes mimic unpalatable species; most common / non-mimic becomes easy prey

7  Sexual selection is natural selection for mating success  It can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics

8  Intrasexual selection is competition among individuals of one sex (often males) for mates of the opposite sex  Intersexual selection, often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates  Male showiness due to mate choice can increase a male’s chances of attracting a female, while decreasing his chances of survival


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