Evolution of Populations and Species Key Idea: Evolution is change over time. Evolution can occur over of thousands of years, as in the evolution of new species, or it can occur over just a generation or two, as in the evolution of populations.
Part 1: Populations A group of individuals of the same species that live in the same area In his theory of evolution by natural selection, Darwin stated that not all of the members of a population are able to survive and reproduce. How then do populations grow?
Exponential growth:
Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate
Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate Will only occur if
Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate Will only occur if there are unlimited resources and conditions are ideal
Exponential growth: growth pattern in which the individuals in a population reproduce at a constant rate Will only occur if there are unlimited resources and conditions are ideal
Logistic growth:
Logistic growth: when a population’s growth slows or stops following a period of exponential growth
Logistic growth: when a population’s growth slows or stops following a period of exponential growth Due to limited resources, most populations in nature experience logistic growth
Logistic growth: when a population’s growth slows or stops following a period of exponential growth Due to limited resources, most populations in nature experience logistic growth
Carrying capacity:
Carrying capacity: the largest number of individuals that a given environment can support The carrying capacity can change based on the environment. It is not a fixed number. If there was a forest fire, the number of trees available to produce nuts would be reduced. As a result the forest could support fewer squirrels.
What factors limit population growth and drive the process of evolution?
Limiting factor:
Limiting factor: a factor that causes population growth to decrease
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors:
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors: a limiting factor that depends on population size
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors: a limiting factor that depends on population size Examples: Competition, predation, parasitism, disease.
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors: a limiting factor that depends on population size Examples: Competition, predation, parasitism, disease. Density-Independent Limiting Factors:
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors: a limiting factor that depends on population size Examples: Competition, predation, parasitism, disease. Density-Independent Limiting Factors: factors that affect all populations in similar ways, regardless of population size
Limiting factor: a factor that causes population growth to decrease They determine which individuals are able to survive and reproduce Density-Dependent Limiting Factors: a limiting factor that depends on population size Examples: Competition, predation, parasitism, disease. Density-Independent Limiting Factors: factors that affect all populations in similar ways, regardless of population size Examples: unusual weather, natural disasters , seasonal cycles
How do we know a population is evolving? Key idea: Populations evolve when the traits of the organisms in the population change over time.
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles Natural selection on traits can lead to changes in , or how common a version of a gene is in the gene pool of the population
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population If the allele frequencies of a population are changing, then the population is
Each individual has two copies of a gene, one from each parent Each individual has two copies of a gene, one from each parent. These copies of genes are called alleles Natural selection on traits can lead to changes in allele frequency , or how common a version of a gene is in the gene pool of the population If the allele frequencies of a population are changing, then the population is evolving Last slide 3/14/2011
Genetic Equilibrium:
Genetic Equilibrium: situation in which allele frequencies remain constant
Genetic Equilibrium: situation in which allele frequencies remain constant If a population is not evolving, the allele frequencies in a population remain stable and genetic equilibrium occurs.
Hardy-Weinberg Equilibrium Principle If these 5 conditions are met, then the population is in equilibrium and is not evolving: There must be random mating The population must be very large There can be no movement into or out of the population No mutations No natural selection
Is genetic equilibrium common in nature?
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H Frequency of h
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H 16 Frequency of h
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H 16 Frequency of h 4
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H 16 Frequency of h 4 Generation 2 Frequency of H Frequency of h
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H 16 Frequency of h 4 Generation 2 Frequency of H 13 Frequency of h
Sample problem Generation 1 Generation 2 HH HH HH HH HH HH HH HH HH HH Frequency of H 16 Frequency of h 4 Generation 2 Frequency of H 13 Frequency of h 7
Did the population evolve from generation 1 to generation 2 Did the population evolve from generation 1 to generation 2? Explain your answer.
Part II: Evolution of Species What is a species? Biological Species Concept:
Part II: Evolution of Species What is a species? Biological Species Concept: a group of similar organisms that can breed and produce fertile offspring Example: Horses and donkeys When you breed a male donkey and a female horse, you get a mule Not officially the same species because the mule infertile and so cannot reproduce
Problem with BSC: Scientists can’t always observe organisms mating Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean. Solution: Scientists can also define species based on , , or .
Problem with BSC: Scientists can’t always observe organisms mating Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean. Solution: Scientists can also define species based on DNA , , or .
Problem with BSC: Scientists can’t always observe organisms mating Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean. Solution: Scientists can also define species based on DNA , morphology , or .
Problem with BSC: Scientists can’t always observe organisms mating Problem with BSC: Scientists can’t always observe organisms mating. The organisms may be extinct or separated by an ocean. Solution: Scientists can also define species based on DNA , morphology , or niche .
Key Idea: New species evolve when populations become reproductively isolated from each other. Reproductive isolation:
Key Idea: New species evolve when populations become reproductively isolated from each other. Reproductive isolation: separation of a species or populations so that they cannot interbreed and produce fertile offspring
Isolating Mechanisms
Isolating Mechanisms Geographic Isolation:
Isolating Mechanisms Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water
Isolating Mechanisms Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water Behavioral:
Isolating Mechanisms Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies
Isolating Mechanisms Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies Temporal:
Isolating Mechanisms Geographic Isolation: When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water Behavioral: When two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies Temporal: When two or more species reproduce at different times
How did Darwin’s finches become new species How did Darwin’s finches become new species? They traveled from the mainland to different islands. Once they were on the different islands, they were isolated from each other by the ocean. This is an example of geographic isolation.
Key Idea: Only populations and species (which are groups of populations) can evolve. Individuals do NOT evolve. Creatures don’t “change” from one thing into another…they remain as they were born. Any changes within an organism’s lifetime are due to acquired characteristics. Remember only genetic changes in the egg and sperm will be passed on to offspring. It is the changes that accumulate over generations in populations or species that lead to changes in organisms over time.
Diagramming Evolutionary History Phylogenetic Tree or Cladograms:
Diagramming Evolutionary History Phylogenetic Tree or Cladograms: diagram that shows the evolutionary relationships among a group of organisms
Reading a Phylogenetic Tree or Cladogram: Species are listed at the end of the branches of the tree. Time is the vertical axis. If an organism’s branch reaches the present, the species is still around today. If an organism’s branch doesn’t reach the present, it is extinct. Traits are written on the tree at the time when they evolved. All organisms that branch off after that trait evolved have that trait.
Reading a Phylogenetic Tree or Cladogram: Common ancestors of organisms are represented by the branching points. Organisms that can trace their branches back to that branching point share that common ancestor. Organisms are more closely related when they share a more recent common ancestor.
Practice Which species is extinct?
Practice Which species is extinct? A
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D?
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species?
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species? B
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species? B Which species are heterotrophs?
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species? B Which species are heterotrophs? B, C, D
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species? B Which species are heterotrophs? B, C, D Which species is a carnivore?
Practice Which species is extinct? A What is the most recent common ancestor of Species B and D? C Species C is most closely related to which species? B Which species are heterotrophs? B, C, D Which species is a carnivore? D
Constructing a Phylogenetic Tree or Cladogram: Organism Backbone Legs Hair Earthworm Absent Trout Present Lizard Human
Constructing a Phylogenetic Tree or Cladogram: Scientists create a character matrix that compares the presence or absence of traits in different organisms. Based on that information, they can construct a tree.
Present Time Past
Present Time Backbone Past
Present Time Legs Backbone Past
Present Hair Time Legs Backbone Past
Present Hair Time Legs Backbone Past
Earthworm Present Hair Time Legs Backbone Past
Earthworm Trout Present Hair Time Legs Backbone Past
Earthworm Trout Lizard Present Hair Time Legs Backbone Past
Earthworm Trout Lizard Human Present Hair Time Legs Backbone Past