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Evolution and Ecology

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Title: Evolution and Ecology


1
Evolution and Ecology
2
Chapter 6 Evolution and Ecology
  • CONCEPT 6.1 Evolution can be viewed as genetic
    change over time or as a process of descent with
    modification.
  • CONCEPT 6.2 Natural selection, genetic drift, and
    gene flow can cause allele frequencies in a
    population to change over time.
  • CONCEPT 6.3 Natural selection is the only
    evolutionary mechanism that consistently causes
    adaptive evolution.

3
Chapter 6 Evolution and Ecology
  • CONCEPT 6.4 Long-term patterns of evolution are
    shaped by large-scale processes such as
    speciation, mass extinction, and adaptive
    radiation.
  • CONCEPT 6.5 Ecological interactions and evolution
    exert a profound influence on one another.

4
Trophy Hunting and Inadvertent Evolution A Case
Study
  • Bighorn sheep populations have been reduced by
    90 by hunting, habitat loss, and introduction of
    domestic cattle.
  • Hunting is now restricted in North America
    permits to take a large trophy ram cost over
    100,000.

5
Figure 6.1 Fighting over the Right to Mate
6
Trophy Hunting and Inadvertent Evolution A Case
Study
  • Trophy hunting removes the largest and strongest
    malesthe ones that would sire many healthy
    offspring.
  • In one population, 10 of males were removed by
    hunting each year.
  • The average size of males and their horns
    decreased over 30 years of study.

7
Figure 6.2 Trophy Hunting Decreases Ram Body and
Horn Size
8
Trophy Hunting and Inadvertent Evolution A Case
Study
  • This is also being observed in other species
  • By targeting older, larger fish, commercial cod
    fishing has selected for genes that result in
    maturation at earlier ages and smaller
    size.Fish that mature earlier can reproduce
    before they are caught, but small fish produce
    fewer eggs.

9
Trophy Hunting and Inadvertent Evolution A Case
Study
  • African elephants are poached for ivory the
    proportion of the population that have tusks is
    decreasing.
  • The unintended effects of human harvesting on
    these animals illustrate how populations can
    change, or evolve, over time.

10
Introduction
  • Humans have a large impact on the
    environmentpollution, land use change, climate
    change, etc.
  • We are just beginning to realize that we also
    cause evolutionary change and the consequences of
    this.
  • Ecology and evolution are strongly interconnected.

11
CONCEPT 6.1 Evolution can be viewed as genetic
change over time or as a process of descent with
modification.
12
Concept 6.1 What Is Evolution?
  • Horn size in bighorn sheep is a heritable trait.
    Trophy hunting selectively eliminates rams with
    large horns, thus favoring rams with genes for
    small horns.
  • Trophy hunting is likely causing the genetic
    makeup of bighorn sheep populations to change, or
    evolve, over time.

13
Concept 6.1 What Is Evolution?
  • Genes are made of DNA and specify (encode)
    protein structure.
  • Genes can have two or more forms called alleles.
  • Genotype is the genetic makeup of an individual.

14
Concept 6.1 What Is Evolution?
  • A genotype is represented by letters, one for
    each allele.
  • One allele is inherited from the mother, one
    from the father.
  • Example Two alleles, A and a individuals could
    be AA, Aa, or aa.

15
Concept 6.1 What Is Evolution?
  • Evolution is change in allele frequencies
    (proportions) in a population over time.
  • For example, if the frequency of a in a
    population is 0.4 or 40, the frequency of A is
    0.6 or 60.
  • If the frequency of a changed to 71, the
    population would have evolved at that gene.

16
Concept 6.1 What Is Evolution?
  • Evolution can be defined more broadly as descent
    with modification.
  • As a population accumulates differences over time
    and a new species forms, it is different from its
    ancestors.
  • But the new species has many of the same
    characteristics as its ancestors and resembles
    them.

17
Concept 6.1 What Is Evolution?
  • Charles Darwin used the phrase descent with
    modification.
  • He proposed that populations change over time
    through natural selection
  • Individuals with certain heritable traits
    survive and reproduce more successfully than
    other individuals.

18
Concept 6.1 What Is Evolution?
  • If two populations experience different
    environmental conditions, different
    characteristics may be favored.
  • Natural selection causes the populations to
    diverge genetically over time.

19
Figure 6.4 Natural Selection Can Result in
Differences between Populations
20
Concept 6.1 What Is Evolution?
  • Natural selection acts as a sorting process.
  • Individuals with favored traits have more
    offspring, and their alleles will increase in
    frequency in the population.
  • The population will evolve, but individuals do
    not evolve.

21
CONCEPT 6.2 Natural selection, genetic drift, and
gene flow can cause allele frequencies in a
population to change over time.
22
Concept 6.2 Mechanisms of Evolution
  • Phenotype Observable characteristics that are
    determined by the genotype.
  • Individuals differ from one another in part
    because they have different alleles for genes.

23
Figure 6.5 Individuals in Populations Differ in
Their Phenotypes
24
Concept 6.2 Mechanisms of Evolution
  • Different alleles arise by mutationa change in
    DNA.
  • Mutations can result from copying errors during
    cell division, mechanical damage, exposure to
    chemicals (mutagens) or high-energy radiation.

25
Concept 6.2 Mechanisms of Evolution
  • Formation of new alleles is critical to
    evolution.
  • If mutation did not produce new alleles, all
    members of a population would have identical
    genotypes and evolution could not occur.

26
Concept 6.2 Mechanisms of Evolution
  • Recombination also produces different genotypes
    within a population.
  • Offspring have combinations of alleles that
    differ from those of their parents.
  • Mutation provides the raw material on which
    evolution is based recombination rearranges the
    raw material into new combinations.

27
Concept 6.2 Mechanisms of Evolution
  • Mutations are actually very rare.
  • In a generation, one mutation would occur in
    every 10,000 to 1,000,000 copies of a gene.
  • In one generation, mutation acting alone causes
    virtually no change in allele frequencies of a
    population.

28
Concept 6.2 Mechanisms of Evolution
  • Three types of natural selection
  • 1. Directional selection Individuals at one
    phenotypic extreme (e.g., large size) are
    favored.
  • Example Drought favored large beak size in
    medium ground finches.

29
Figure 6.6 Three Types of Natural Selection
(Part 1)
30
Concept 6.2 Mechanisms of Evolution
  • 2. Stabilizing selection Individuals with an
    intermediate phenotype are favored.Example
    Parasitic wasps select for small gall size of
    Eurosta flies while birds select for large gall
    size.

31
Figure 6.6 Three Types of Natural Selection
(Part 2)
32
Concept 6.2 Mechanisms of Evolution
  • 3. Disruptive selection Individuals at both
    phenotypic extremes are favored.
  • Example African seedcrackers (birds) have
    two food sourceshard seeds that require large
    beaks to crack, and smaller, softer seeds that
    smaller beaks are more suited to.

33
Figure 6.6 Three Types of Natural Selection
(Part 3)
34
Concept 6.2 Mechanisms of Evolution
  • Natural selection can result in populations in
    which all individuals have the favored allele
  • Andean geese have evolved a type of hemoglobin
    with a very high affinity for O2, an advantage at
    high altitudes.
  • The allele frequency for this trait is 100.

35
Concept 6.2 Mechanisms of Evolution
  • Genetic drift occurs when chance events determine
    which alleles are passed to the next generation.
  • It is significant only for small populations.

36
Concept 6.2 Mechanisms of Evolution
  • Genetic drift has four effects on small
    populations
  • 1. It acts by chance alone, thus causing allele
    frequencies to fluctuate at random.
  • Some may disappear, others may reach 100
    frequency (fixation).

37
Figure 6.7 Genetic Drift Causes Allele
Frequencies to Fluctuate at Random
38
Concept 6.2 Mechanisms of Evolution
  • 2. Because some alleles are lost, genetic
    variation of the population is reduced.
  • 3. Frequency of harmful alleles can increase if
    the alleles have only mildly deleterious effects.
  • 4. Differences between populations can increase.
    Chance events may lead to allele fixation in one
    population and loss from another population.

39
Concept 6.2 Mechanisms of Evolution
  • 2 and 3 can have dire consequences.
  • Loss of genetic variation reduces the ability of
    the population to respond to changing
    environmental conditions.
  • Increase of harmful alleles can reduce survival
    and reproduction.
  • These effects are important for species that are
    near extinction.

40
Concept 6.2 Mechanisms of Evolution
  • Gene flow Alleles move between populations via
    movement of individuals or gametes.
  • Gene flow has two effects
  • 1. Populations become more similar.
  • 2. New alleles can be introduced into a
    population.

41
CONCEPT 6.3 Natural selection is the only
evolutionary mechanism that consistently causes
adaptive evolution.
42
Concept 6.3Adaptive Evolution
  • Adaptations are features of organisms that
    improve their ability to survive and reproduce.
  • Adaptations include morphological and
    physiological features such as enzymes that
    function at high temperatures.

43
Figure 6.11 Adaptive Evolution in Soapberry Bugs
44
Concept 6.3Adaptive Evolution
  • Rapid adaptive evolution can happen on a
    continental scale.
  • Clines are patterns of change in a characteristic
    over a geographic region.

45
Figure 6.12 Rapid Adaptive Evolution on a
Continental Scale
46
Concept 6.3Adaptive Evolution
  • Adaptive evolution is driven by ecological
    interactionsorganisms interacting with one
    another and with their environment.
  • Ecology is a basis for understanding natural
    selection.

47
CONCEPT 6.4 Long-term patterns of evolution are
shaped by large-scale processes such as
speciation, mass extinction, and adaptive
radiation.
48
Concept 6.4The Evolutionary History of Life
  • Species Group of organisms whose members have
    similar characteristics and can interbreed.
  • Speciation The process by which one species
    splits into two or more species.

49
Concept 6.4The Evolutionary History of Life
  • Speciation most commonly occurs when a barrier
    prevents gene flow between two or more
    populations of a species.
  • Barriers can be geographic or ecological. The
    populations then diverge genetically over time.

50
Figure 6.14 Speciation by Genetic Divergence
51
Concept 6.4The Evolutionary History of Life
  • The key step in speciation occurs when a
    population accumulates so many genetic
    differences that they cannot produce viable,
    fertile offspring if they mate with the parental
    species.

52
Concept 6.4The Evolutionary History of Life
  • Repeated speciation events increases the number
    of species in a group, but some species are also
    lost to extinction.
  • An evolutionary tree is a branching diagram that
    represents the evolutionary history of a group.

53
Figure 6.16 An Evolutionary Tree of the
Pinnipeds (Part 1)
54
Figure 6.18 The Big Five Mass Extinctions
55
Concept 6.4The Evolutionary History of Life
  • Each mass extinction was followed by an adaptive
    radiation Increased diversity of the surviving
    groups.
  • Mass extinctions remove competitor groups,
    allowing survivors to expand into new habitats or
    new ways of life.

56
Concept 6.4The Evolutionary History of Life
  • Adaptive radiations can also occur when a group
    evolves major new adaptations.
  • Example Stems that provide support and waxy
    cuticles that prevent drying allowed adaptive
    radiation of terrestrial plants.

57
Concept 6.4The Evolutionary History of Life
  • Biological communities are devastated by mass
    extinction events.
  • It takes millions of years for diversity to
    increase to the levels seen prior to the mass
    extinction.
  • This has great implications if human activities
    cause a sixth mass extinction.

58
Concept 6.4The Evolutionary History of Life
  • Coevolution Reciprocal evolutionary change in
    interacting species.

59
CONCEPT 6.5 Ecological interactions and evolution
exert a profound influence on one another.
60
Concept 6.5Joint Effects of Ecology and Evolution
  • The sunflower Helianthus anomalus arose as a
    hybrid between two other species.
  • The hybrid has new gene combinations that allow
    it to grow in a different environment than the
    parent species.
  • In the new environment, the hybrid became a new
    species.

61
Figure 6.21 A Hybrid That Lives in a New
Environment
62
Concept 6.5Joint Effects of Ecology and Evolution
  • Hybridization resulted in an ecological shift
    that illustrates how evolution influences
    ecology.
  • But life under different ecological conditions
    provided the selection pressures that molded the
    hybrid into a new species, showing how ecology
    influences evolution.

63
Concept 6.5Joint Effects of Ecology and Evolution
  • Evolution can result from a range of ecological
    interactions, including predation, competition,
    herbivory, parasitism, and mutualism.
  • Speciation is often caused by ecological factors.

64
Concept 6.5Joint Effects of Ecology and Evolution
  • Evolution can alter ecological interactions.
  • If a predator evolves a new way to capture prey,
    they prey species may go extinct, decline,
    migrate to other areas, or evolve new ways to
    cope with the more efficient predator.

65
Connections in Nature The Human Impact on
Evolution
  • When human actions drive a species to extinction,
    the course of evolution is altered.
  • Many scientists think humans are causing a sixth
    mass extinction.
  • If so, our actions will greatly and irreversibly
    change the evolutionary history of life on Earth.
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