Ch 11 The Evolution of Populations

Objectives 7B analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and sequential nature of groups in the fossil record; 7C analyze and evaluate how natural selection produces change in populations, not individuals; 7D analyze and evaluate how the elements of natural selection, including inherited variation, the potential of a population to produce more offspring than can survive, and a finite supply of environmental resources, result in differential reproductive success 7E analyze and evaluate the relationship of natural selection to adaptation and to the development of diversity in and among species; 7F analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene flow, mutation, and recombination

Section 11.1 Genetic Variation within Populations 1.Genetic variation increases the chances of some individuals surviving a.In a population there are a wide range of phenotypes (a trait produced by one or more genes) b.Natural selection acts on different phenotypes in a population, and phenotype is determined by genotype c.More genetic diversity = more phenotypic diversity

Section 11.1 Genetic Variation within Populations d.Greater variation in phenotype, the more likely some individuals will survive a.Penguin example (short and round vs tall and slim in cold/famine conditions) e.Gene pool- the combined alleles of all the individuals in a population f.Allele frequency- how common a certain allele is

Section 11.1 Genetic Variation within Populations 2.Genetic Variation a.Two main sources of genetic variation are i.Mutations- random change in DNA, forming new alleles. Only works if the mutation is in reproductive (sperm and egg) cells ii.Recombination- occurs during meiosis and results in new gene combinations

Section 11.2 Natural Selection in Populations 1.Natural selection acts on distributions of traits (phenotypes) a.Normal distribution- common when all phenotypes provide an equal chance of survival. Occur where the frequency of a trait is highest around the average i.But environments can change! ii.Microevolution- the observable change in allele frequencies of a population over time (does not lead to a new species)

Section 11.2 Natural Selection in Populations 1.Directional selection- selection that favors one extreme phenotype. Causes a shift is phenotypic distribution EX: oysters with thicker shells cannot be eaten by crabs, so thick shells becomes common 2.Stabilizing selection- selection that favors the intermediate (middle) phenotype EX: Both white and black moths are easy for predators to find on grey bark, so the grey phenotype is selected 3.Disruptive selection- occurs when both extreme phenotypes are favored EX: blue birds get mates, brown birds are camouflaged from predators, but bluish brown birds have neither benefit

Section 11.2 Natural Selection in Populations directional stabilizing disruptive

Section 11.2 Natural Selection in Populations If all human females suddenly only dated short guys, what type of selection would occur What trait would become more common in the human population?

Section 11.3 Other Mechanisms of Evolution 1.Gene flow- the movement of alleles between populations a.Gene flow can increase genetic variation of the receiving population and keeps gene pools similar

Section 11.3 Other Mechanisms of Evolution 2.Genetic drift- changes in allele frequency due to random chance, usually works only on small populations a.Two processes can cause populations to become small enough for genetic drift to occur i.Bottleneck effect- what occurs after an event that greatly reduces population size ii.Founder effect- what occurs after a small number of individuals colonize a new area b.Genetic drift can cause problems, including Less genetic variety Lethal genes can become more common

Section 11.3 Other Mechanisms of Evolution Bottleneck-a destructive event that leaves only a few survivors a. overhunting a population reducing the variations

Section 11.3 Other Mechanisms of Evolution Founder-allelles from yellow flowers increase in new small population

Section 11.3 Other Mechanisms of Evolution 3.Sexual selection- when certain traits increase mating success a.Females tend to be more selective, as eggs are few and expensive b.Two types of sexual selection i.Intrasexual selection- males compete with each other for females ii.Intersexual selection- males display to attract a female

Section 11.3 Other Mechanisms of Evolution c.Traits that increase mating success are not always adaptive or advantageous for the survival of an organism

Section 11.3 Other Mechanisms of Evolution 4.5 factors that can lead to evolution a.Gene flow b.Genetic drift c.Mutation d.Sexual selection e.Natural selection

Section 11.3 Other Mechanisms of Evolution Male Irish Elk, now extinct, had 12 foot wide antlers. Describe what could have lead to this trait

Section 11.5 Speciation through Isolation 1.Isolation of populations can lead to speciation a.Reproductive Isolation- when members of different populations (same species) can no longer mate successfully b.Speciation- the rise of two or more species from one existing species

Section 11.5 Speciation through Isolation 2.Populations can become isolated in several ways a.Behavioral isolation- isolation caused by differences in courtship or mating behaviors EX: fireflies- different species flash at different intervals b.Geographic isolation- a physical barrier divides a population into 2 or more groups EX: a river cuts a rabbit population in half c.Temporal isolation- when timing prevents reproduction between populations EX: some birds mate in winter, some in summer

Section 11.5 Speciation through Isolation

Section 11.6 Patterns in Evolution 1.Evolution through natural selection is not random a.Individuals with traits that are better adapted for their environment have a better chance of surviving and reproducing then individuals without those traits b.The environment controls the direction of selection, and environments can change

Section 11.6 Patterns in Evolution c.Convergent evolution- evolution towards similar characteristics in unrelated species. Analogous structures are common examples- shark fins vs whale fins d.Divergent evolution- when closely related species evolve in different directions. Kit fox vs Red fox.

Section 11.6 Patterns in Evolution 2.Species can shape each other over time a.Coevolution- when two or more species evolve in response to each other i.Evolutionary arms race- crab and snail example

Section 11.6 Patterns in Evolution 3.Extinction- the elimination of a species from earth a.Background extinctions- occur continuously but at low rates b.Mass extinction- destroy many species quickly. Usually the result of catastrophic event like an ice age or asteroid impact. There have been 5 during earth’s history and we are in the middle of a sixth now

Section 11.6 Patterns in Evolution 4.Patterns of speciation a.Gradualism- species evolve slowly over long periods of time b.Punctuated equilibrium- episodes of speciation occur suddenly and are followed by long periods of little change. i.Adaptive radiation- the rapid evolution of many diverse species from ancestral ones. Usually follows a catastrophic event or after a species colonizes a new area

Section 11.6 Patterns in Evolution