Natural Selection Mechanism of Evolutionary Change Theory of

Natural Selection Mechanism of Evolutionary Change

Theory of Natural Selection • Gradual process by which traits become either more or less common in a population

Principles of Natural Selection Overproduction Inherited Variation Competition Selection

Natural Selection Observation 1 Organisms generally have more offspring than can survive to adulthood. Observation 2 Offspring are not identical. There is variation in their appearance, size, and other characteristics. Observation 3: Organisms that are better adapted to their environment have a greater likelihood of surviving and passing these characteristics on to their offspring.

Natural Selection: Mechanism of Evolution Individuals has specific inherited characteristics They produce more surviving offspring Population includes more individuals with specific characteristics Population evolves and is better adapted to its environment

Overproduction Population produces more offspring than can possibly survive http: //phet. colorado. edu/en/simulation/naturalselection Too many offspring = weakest ones will die and not pass on their traits

Inherited Variation • Variation in a characteristic that is a result of genetic inheritance

Competition Too few resources, Beneficial traits will be passed on, Non-beneficial traits will be “lost” eventually

Selection The best at survival will pass on their traits Those who survive the struggle will have good adaptations

Survival of the “fittest” • The reproductive ability of an organism

What Is Adaptation? Any change in the structure/functioning of an organism that makes it better suited to its environment

Camouflage & Mimicry To escape from predators Sneaking up on prey Camouflage - directional selection favors individuals who most resemble environment Mimicry - directional selection can favor individuals who most resemble something harmful

Symbiosis

Three Types of Symbiosis • Mutualism § Both species benefit • Commensalism § One species benefits, the other is unaffected • Parasitism § one species benefits, the other is harmed

Mutualism Both organisms benefit from the relationship The otters help the kelp by eating the sea urchins which endanger it. The kelp provides and anchor for the otters while they sleep.

Commensalism One species benefits while the other is unaffected The cattle egret and cows The cattle help the egret who look for grasshoppers and beetles that are raised by the cows. Now and then they sit on the back of a cow, looking for ticks and flies.

Parasitism One species benefits while the other is harmed Mistletoe lives off the tree that it attaches to Without that tree it would die It slowly chokes out the life of the host tree

Five Agents of Microevolution 1. Genetic drift • Random change in population due to catastrophic events Bottleneck Effect • Population destroyed • Characteristics of species determined by surviving organism Founder Effect • Establishment of new population when one species is randomly separated from the original

Five Agents of Microevolution 2. Mutation Error in DNA sequences 3. Gene Flow Change a gene pool due to the movement of genes into or out of a population

Five Agents of Microevolution 4. Nonrandom Mating Individuals have more opportunity to reproduce than others of the same species 5. Natural selection Leads to differential reproductive success

Directional Selection Natural selection favors both extremes Neck of Giraffe Antibiotic resistance of bacteria Moth color (melanin) Camouflage/Mimics Many sexually selected traits

Stabilizing Selection When the extremes of the trait aren’t as well suited Examples bird clutch size Elk Antlers size Giraffe neck length Tail length in birds

Disruptive Selection Causes divergence within the species Occurs when two different types of resources in one area Results in specialization for each branched group May lead to formation of new species E. g. Darwin’s Finches

Main Types of Selection Pressures Disruptive Selection Natural selection favors both extremes Stabilizing Selection Natural selection favors the average for population Directional Selection Natural selection favors one extreme of the population