Evolution by Means of Natural Selection: The Development of Adaptations to Survive

Slide # 2 Important Vocabulary 1. Adaptation: physical or behavioral trait that helps an individual survive & reproduce in its environment. Makes them more “fit” 2. Fit or Fitness: success at surviving & reproducing 3. Gene Pool: all alleles (forms of genes) shared within a species 4. Frequency: how often an allele is seen in the gene pool How does its coloration help the Snowy Owl survive in its habitat? What other adaptations does it have that makes it “fit” for its environment?

Requirements for Natural Selection: Variation Exists in Nature Slide # 3 Requirements for Natural Selection: Variation Exists in Nature Variation is inheritable New variations come from mutations in DNA. Some mutations are harmful & some are helpful.

Tendency towards overpopulation Slide # 4 Requirements for Natural Selection: More offspring are produced than will survive. Tendency towards overpopulation b. Strategy for survival: Many species lay tons of eggs; some will survive to adulthood

Slide # 5 Requirements for Natural Selection: There is a constant struggle for survival. Competition for limited resources food, space, territory, shelter (nesting sites) & mates Wolf chasing raccoon

Slide # 6 Requirements for Natural Selection: 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 & produce more offspring than less “fit” individuals. The most “fit” individuals are best adapted to that particular environment. If environment changes, different variations may be selected to be more fit

Slide # 7 Requirements for Natural Selection: 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. Separated by a glacier during the last Ice Age, two different species of meadowlark evolved. Eastern Meadowlark Western Meadowlark

Mutations in Genes: the Source of all new Variations Slide # 8 Mutations in Genes: the Source of all new Variations 1. Helpful mutations lead to adaptation by increasing fitness & decreasing the death rate Frequency of helpful mutation will increase in the population as more individuals survive & leave offspring 2. Harmful mutations decrease fitness of the individual in that environment & cause a higher mortality rate Frequency of the mutation will decrease & might or might not disappear from the gene pool How is the fruit fly on the bottom different from the fruits above?

Helpful Mutations (Adaptations) Slide # 9 Helpful Mutations (Adaptations) The woodpecker’s sharp beak allows it to drill into trees to catch insects. Adaptations of Birds Feet

Adaptations: A Result of Compromise Slide # 10 Adaptations: A Result of Compromise An adaptation may work really great for some things (reaching food) , but they may prose a problem for other things (drinking water)

Camouflage: A Helpful Adaptation Slide # 11 Camouflage: A Helpful Adaptation 1. Camouflage: having a shape / color that blends in with the environment 2. Difficult for predators to see the prey Find the canyon tree frog! Find the green leaf mantid!

Mimicry: Taking Advantage of Another’s Coloration Slide # 12 Mimicry: Taking Advantage of Another’s Coloration 1. Mimicry: when a harmless individual looks like a similar, harmful (poisonous) individual 2. Predators learn to avoid both Viceroy: looks poisonous monarch Monarch is poisonous

Slide # 13 Speciation: Often Begins with a Physical Separation From the Original Population Grand Canyon is NOT a physical barrier for all species. What kind of organisms would be able to cross the canyon? 1. Geographic isolation: a barrier that physically separates members of a species into two or more groups EX: Mountains, large body of water (lake or ocean), volcanic eruption, canyon, road A barrier may physically separate some species, but not others

Reproductive Isolation Leads to Speciation Slide # 14 Reproductive Isolation Leads to Speciation Mutations cause changes in chromosome number Humans are the only primates that have 46 chromosomes Members of an original species can no longer breed together to produce fertile offspring. – Cannot interbreed. Three species of Flycatcher. Reproductive Isolation keeps these as three separate species. Why? Females only respond to mating call of males that are like them.

Slide # 15 Temporal Isolation Temporal isolation: differences in mating times / seasons Because they mate at different times, the wood frog and the leopard frog remain separate species and hybrids are not produced

Natural Selection at Work: The Peppered Moths Slide # 16 Natural Selection at Work: The Peppered Moths Before After Before the industrial revolution in England (1850), the frequency was higher for light peppered moths than the dark peppered moths. After the start of the industrial revolution, the frequency of dark peppered moth was higher than the light peppered moth.

Effects of Natural Selection: Directional Selection Slide # 17 Effects of Natural Selection: 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. 2. Can lead one population evolving into a new species. Food becomes scarce. Notice the shift in beak size

Effects of Natural Selection: Stabilizing Selection Slide # 18 Effects of Natural Selection: Stabilizing Selection 1. Stabilizing selection: members in the center of the distribution curve have a higher fitness than those at each end. 2. This type of selection favors average individuals. 3. Reduces variation in a population; evolution is not likely to happen. 4. Ex: babies that are between 6 & 8 pounds at birth have a better chance of surviving 1st year of life.

Stabilizing Selection Slide # 19 Stabilizing Selection In the example below, averaged size spiders survive more often, because birds eat the very large and small ones.

Effects of Natural Selection: Disruptive Selection Slide # 20 Effects of Natural Selection: Disruptive Selection 1. Disruptive selection: when members at BOTH ends of the distribution curve have a higher fitness than those in the middle 2. In some cases, there are no intermediate forms. 3. This can lead to the evolution of two new species. Population splits into two subgroups specializing in different seeds. Number of Birds in Population Beak Size

Remember: Individuals Do not Change to Fit the Environment