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Transcript of Evolution & Biodiversity Chapter 5. Origins of life Chemical analysis and measurement of radioactive...
![Page 1: Evolution & Biodiversity Chapter 5. Origins of life Chemical analysis and measurement of radioactive elements in rocks & fossils are studied Evolution.](https://reader030.fdocuments.in/reader030/viewer/2022032803/56649e2b5503460f94b197c2/html5/thumbnails/1.jpg)
Evolution & Biodiversity
Chapter 5
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Origins of life
• Chemical analysis and measurement of radioactive elements in rocks & fossils are studied
• Evolution of life is linked to evolution of earth
• Life evolved over the past 4.7 - 4.8 billion years
• Chemical evolution came first
• Biological evolution - about 2.3 - 2.5 billion years ago
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Origins of LifeOrigins of Life
Chemical evolutionChemical evolution
Biological evolutionBiological evolution
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How origins are studied
• Fossils
• Fossil record is uneven and incomplete
• Why? Some organisms left no fossils - some have decomposed and some are not yet found.
• It is believed we have fossils representing about 1% of all organisms ever living on earth
• Also use :– chemical and radioactive
dating
– Ancient rocks
– Ice cores
– DNA from living organisms
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Evolution & adaptation
• Within limits, populations adapt to changes in their environment - called biological evolution - change in genetic make-up in a population through successive generations
• POPULATIONS, NOT INDIVIDUALS EVOLVE BY BECOMING GENETICALLY DIFFERENT.
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• THEORY OF EVOLUTION - all species descended from earlier, ancestral species
• Microevolution – Small genetic changes
that occur in a population
• Macroevolution - – Long-term, large-scale
evolutionary changes among groups of species - new species are formed from ancestral species and other species are lost through extinction.
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Microevolution
• Development of genetic variability in a population– Gene pool – set of all
genes in the individuals of the population of a species
• Alleles - genes have two or more different molecular kinds
• These are recombined• Each member of
population gets different combination of alleles
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Mutation
• Random change in structure of number of DNA molecules in a cell
• Can occur in two ways:– Exposure to external agents such as radioactivity, x-
rays, natural and man-made chemicals
– Random changes in coded genetic instructions.
Sometimes are beneficial and make survival easier under existing or changing conditions.
Some are harmless and some are lethal.
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• Mutations are:– Random and unpredictable– Only new source of genetic material– Rare events
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Mutation
• Random changes in structure or number of DNA molecules in a cell
• Can be caused by radiation and chemicals - mutagens
• Random mistakes
• Can occur in any cell but only passed on in reproductive cells.
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• Natural selection occurs when some individuals have genetically based traits that cause them to better survive and produce offspring
• Idea developed by Charles Darwin in “On the origin of the species by means of natural selection”
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More…
• Must be natural variability for a trait in a population
• Trait must have a genetic bases that can be passed from one generation to another – be heritable
• Must lead to differential reproduction - enable individuals with the trait to leave more offspring than other members of the population.
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Adaptations or adaptive traits
• A heritable trait that enables organisms to better survive and reproduce under a given set of environmental conditions
• Selective pressure - a factor in a population’s environment that causes natural selection to occur.
• Environmental conditions do not create favorable characteristics
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To summarize
• Genes mutate
• Individuals are selected
• Populations evolve
• Can also change populations by artificial selection (see p. 100)
• Peppered moth - an example
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Types of natural selection
• Directional natural selection - conditions shift so that individuals at one end of the normal range become more common than midrange forms - “it pays to be different”
• Most common during periods of environmental change or when members of a population migrate to a new habitat with different environmental conditions.
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Second type:
• Stabilizing natural selection - eliminates individuals at both ends of the genetic spectrum and favors average genetic make-up
• “it pays to be average”
• Occurs when an environment changes little and members are well adapted to that environment.
• Individuals with unusual alleles tend to be eliminated
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Third type:
• Diversifying natural selection - disruptive natural selection - individuals at both extremes of the genetic spectrum are favored and individuals with normal traits are eliminated.
• “It doesn’t pay to be normal”
• Population is split into two groups
• Occurs when there is a shift in food supply selected against average individuals
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Coevolution
• Populations of two different species interact over a long time and changes in one gene pool lead to changes in the gene pool of another species
• Owls become better at hunting mice; certain prey have traits that allow them to escape
• Some of the predators have better eyesight and are more successful hunters and they pass this trait to their offspring.
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Ecological niche
• Way of life or role in the ecosystem
• Involves everything that affects survival and reproduction
• Includes: range of tolerance for chemical and physical requirements
• Important because:– Can prevent extinction– Can help assess
environmental changes.
• Types of resources used - food or nutrients
• How it interacts with biotic and abiotic factors
• Role in the flow of energy and matter cycling
• Represents adaptive traits that organisms have acquired through evolution that allow for better survival.
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Fundamental niche
• The full potential range of physical, chemical, and biological conditions and resources an organism could theoretically use if there was no competition with other species.– Niches however, often overlab
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Realized niche
• In order for an organism to survive and avoid competition for resources it will use only part of its fundamental niche – this is the realized niche.
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Generalist species
• Occupy broad niches
• Can live many places
• Eat many types of food
• Tolerate a wide range of environmental conditions
• Flies, cockroaches, mice, etc
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Specialist species
• Have narrow niches• Live in only one type of habitat• Eat only one or a few types of food• Tolerate only a narrow range of climactic and
environmental conditions• More prone to extinction during changes in
environmental conditions• Examples: tiger salamander, red-cockaded
woodpecker, spotted owls, giant panda
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Limits to adaptation
• Changes in environmental conditions can lead to adaptation only if the traits are already present in the gene pool
• Because each organism must do many things
• Adaptations are usually compromise
• Even if a beneficial trait is present, the population’s ability to adapt is limited by its reproductive capacity
• Adapt, migrate or die
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Convergence or convergent evolution
• Species with similar niches tend to evolve similar traits that enable them to survive and reproduce even though they are in different parts of the world
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macroevolution
• Evolution that takes place above the level of species and over much longer periods
• Patterns include:– Genetic persistence -
inheritance of DNA molecule through all subsequent lines of descent
– Genetic divergence - long term changes in lineages of species
– Genetic losses - steady loss (background extinction) or abrupt, catastrophic loss (mass extinction) of lineages
– Example: the horse
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How do new species evolve?
• Speciation - two species arise from one
• Usually takes place in two phases:– Geographic isolation -
• Populations become separated for long periods of time
• Migration to new area
• Physical barrier such as a road
• Earthquake
– Reproductive isolation -
• Mutation & natural selection act on isolated populations - called divergence - eventually cannot interbreed
– Divergent evolution - arises from speciation
– Usually takes tens of thousands of years
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Speciation
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Extinction
• Can be caused by large scale movement of the continents (continental drift)
• Gradual climate change
• Rapid climate change - volcanic eruption, etc.
• Extinction is the ultimate fate of all organisms
• Biologists estimate that 99.9% of all species that have ever lived are now extinct.
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Types of extinction
• Background extinction - species disappear at a low rate as local conditions change
• Mass extinction - abrupt rise in extinction rates - catastrophic, often global-wipes out large groups of species
• Generally believed to be the result of climate change.
• Five mass extinction s - 20 - 40 million years apart– Last one took place
about 65 million years ago - wiped out the dinasaurs
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Adaptive radiations
• Periods of recovery• Numerous new species
evolve over several million years to fill niches vacated by extinct species
• Explosion of mammals after dinosaurs became extinct
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Biodiversity =
• Speciation minus extinction• Humans have become a major force in the
premature extinction of species.• We may cause extinction of up to a quarter of
the earth’s current species• On short time scale, new species cannot form
rapidly enough• We are impacting the earth