Evolution by Means of Natural Selection: Mechanisms of Natural Selection Chapter 11

Important Vocabulary 1.Adaptation: physical or behavioral trait that helps an individual survive and reproduce in its environment. Makes them more fit 2.Fit or Fitness: measure of an organisms’ ability to survive and reproduce 3.Natural Selection: variation being selected on in a population by the environment, this typically leads to an increase in an individual’s fitness 4.Artificial Selection: Nature provided the variation, and humans selected those variations that they found useful. How does its coloration help the Snowy Owl survive in its habitat? Makes it harder to be seen by predators. What other adaptations does the owl possess that makes it more “fit” for its environment? Lots of feathers for warmth, etc.

Before the industrial revolution in England (1850), the likelihood of seeing light peppered moths was higher than the dark peppered moths. Before After After the start of the industrial revolution, the likelihood of seeing dark peppered moths was higher than the light peppered moth. READ: Natural Selection at Work: The Peppered Moths This was due to the dark colored pollution in the air that covered the light surfaces during the revolution. The pollution made it easier for predators to see the white moths. The predators would eat the white moths and the dark moths would survive to pass on their genes for dark coloration.

Variation is inheritable and can be caused randomly due to genetics and other processes Variations can be helpful, harmful, or neutral. Biodiversity (Biological diversity) = Sum total of the genetically based variety of all organisms in the biosphere. Requirements for Natural Selection: 1. Variation Exists in Nature

Not all individuals of a population will survive long enough to reproduce, therefore there is a tendency towards overpopulation One strategy for survival: Many species lay many eggs in hopes that some will survive to adulthood in order to reproduce. Requirements for Natural Selection: 2. More offspring are produced than will survive.

Requirements for Natural Selection: 3. There is a constant struggle for survival. Competition for limited food supply, space, territory, shelter (nesting sites) and mates is always occurring. Organisms compete in order to survive and reproduce Predator and prey relationships create a strong pressure for change Adaptations are the potential results of these relationships Wolf chasing raccoon

Requirements for Natural Selection: 4. Some individuals in the species will have variations that cause them to be the most fit in a particular environment. The fittest individuals will survive the longest and produce more offspring than less fit individuals. The most fit individuals are better suited or adapted to that particular environment. If the environment changes, then different variations may be selected for that allow an individual to be more fit in that environment.

Requirements for Natural Selection: 5. Vast amount of time is required for a species to change After many generations there will be enough genetic change in the population to produce a new species. Eastern Meadowlark Western Meadowlark Separated by a glacier during the last Ice Age, two different species of meadowlark evolved.

Mutations in genes is the source of all new variations 1.Helpful mutations lead to adaptation by increasing fitness & decreasing the death rate Frequency of helpful mutation (gene) will increase in the population as more individuals survive & leave offspring How is the fruit fly on the bottom different from the fruits above?

Camouflage: having a shape or color that blends in with the environment Difficult for predators to see the prey Find the green leaf mantid! Find the canyon tree frog! Helpful Mutations:

Mimicry: Taking Advantage of Another’s Coloration Mimicry: when a harmless individual looks like a similar, harmful (poisonous) individual Predators learn to avoid both Viceroy: looks like poisonous monarch Monarch is poisonous Helpful Mutations:

Adaptations of Birds Feet The woodpecker’s sharp beak allows it to drill into trees to catch insects. Helpful Adaptations: Examples

The giraffe’s long neck helps it reach higher in the tree for food where other animals can’t. The alternating black & white stripes help keep zebras cool. Black stripes absorb heat & white stripes reflect heat.

Adaptations: A Result of Compromise An adaptation may work really great for some things like reaching food, but they may pose a problem for other things such as drinking water.

Adaptations That Increase Fitness are Inherited Variations! Remember: Individuals Cannot Change to Fit the Environment!

Mutations in genes is the source of all new variations 2. Harmful mutations will decrease fitness of the individual in that environment & cause a higher mortality rate Frequency of the mutation (gene) decreases = might or might not disappear from the gene pool Gene Pool - Consists of all genes, including all the different alleles, that are present in a population. How is the fruit fly on the bottom different from the fruits above?

Other sources of variation Natural selection is not the only source of evolutionary change. In small populations, an allele can become more or less common simply by chance.

Other sources of variation 1. Genetic Drift - Random change in allele frequencies that occurs in small populations. Happens by chance - such as random mating or a natural disaster (fire, landslide or lightning strike). Doesn’t work to produce adaptations like natural selection does.

Other sources of variation 2. Gene Flow - The transfer of alleles or genes from one population to another; also known as gene migration. Affected by: 1.Mobility- ability to move 2.Barriers- physical and behavioral

SPECIES - A GROUP OF SIMILAR LOOKING ORGANISMS THAT CAN BREED TOGETHER TO PRODUCE FERTILE OFFSPRING. (FERTILE- ABLE TO REPRODUCE). What mechanisms lead to speciation?

Reproductive Isolation Leads to Speciation Speciation: Members of an original species can no longer breed together to produce fertile offspring. They are considered two separate species. Three species of Flycatcher. Reproductive Isolation keeps these as three separate species. Why? Females only respond to mating call (song) of males that are like them Behavioral Isolation Example Mechanisms that lead to speciation

What mechanisms lead to reproductive isolation? 1.Geographic isolation: barrier that physically separates members of a species into two or more groups a. EX: Mountains, large body of water (lake or ocean), volcanic eruption, canyon, road b.A barrier may physically separate some species, but not others Grand Canyon is NOT a physical barrier for all species. What kind of organisms would be able to cross the canyon? Mechanisms that lead to speciation

Reproductive isolation can occur by: 2. Behavioral Isolation: Two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies that involve behavior Mechanisms that lead to speciation

3. Temporal Isolation - Form of reproductive isolation in which two populations reproduce at different times. –Example: –Three similar species of orchid all live in the same rain forest. –Each species releases pollen only on a single day. –Because the three species release pollen on different days, they cannot pollinate one another. Mechanisms that lead to speciation

Three types of Natural Selection: A. Directional Selection 1.Directional selection: members at one end of distribution curve have a higher fitness than those in the middle or at the other end of the curve. Can lead to one population evolving into a new species. Food becomes scarce. Notice the shift in beak size

Directional Selection The woodpeckers with the longer beaks are more fit for this environment, so there are more of them than woodpeckers with shorter beaks. Selection for longer beaks

B. Stabilizing Selection 1.Stabilizing selection: members in the center of the distribution curve have a higher fitness than those at each end. Favors average individuals. Reduces variation in a population; evolution is not likely to happen. Ex: babies that are between 6 & 8 pounds at birth have a better chance of surviving 1 st year of life.

Stabilizing Selection In the example below, averaged size spiders survive more often, because birds eat the very large and small ones.

C. Disruptive Selection 1.Disruptive selection: when members at BOTH ends of the distribution curve have a higher fitness than those in the middle In some cases, there are no intermediate forms. This can lead to the evolution of two new species. Number of Birds in Population Beak Size Population splits into two subgroups specializing in different seeds.

Selection for dark limpets In the example below, the light and dark limpets (Clams) are camouflaged, whereas the intermediate ones are not, and are eaten. Disruptive Selection

Matching Practice (Types of Selection): A. Directional B. Stabilizing C. Disruptive 1.Does not lead to speciation or evolution. 2.Cause one species to evolve into two different species. 3.Causes one species to evolve into a different species. 4.Type of selection that favors one extreme variation. 5.Type of selection that favors the average variation. 6. Type of selection that favors the two extreme variations.

Gradualism, Punctuated Equilibrium and Genetic Equilibrium How long does it take for evolution to occur? Does evolution always occur?

Gradualism vs. Punctuated Equilibrium How quickly does evolution occur? –Gradualism – Long time with gradual change. –Punctuated Equilibrium - Long, stable periods interrupted by brief periods of more rapid change.

Evolution vs. Genetic Equilibrium To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes place. So biologists ask: Are there any conditions under which evolution will not occur? –The answers to those questions are provided by the Hardy-Weinberg principle.

Hardy-Weinberg Principle Five conditions are required to maintain genetic equilibrium from generation to generation: 1.There must be random mating. 2.The population must be very large. »Genetic drift has less effect on large populations than on small ones.

Hardy-Weinberg Principle 3. There can be no movement into or out of the population. »Individuals may bring new alleles into a population. 4. There can be no mutations. 5. There can be no natural selection. »No phenotype can have a selective advantage over another.

Two Patterns of Evolution- 1. Divergent Evolution (adaptive radiation)- type of evolution in which one species evolves into two separate species because it is adapting to different environmental situations 2. Convergent Evolution- type of evolution in which two unrelated species evolve similar characteristics because they are both adapting to the same environmental situations

Divergent Evolution or Adaptive Radiation Raven and Johnston, Biology

Divergent Evolution Raven and Johnston, Biology

Convergent Evolution Raven and Johnston, Biology