Download How has life changed since the formation of earth?

September 30, 2014
Chapter 4: Evolution and Biodiversity
Did the earth always look like it
did today?
How has life changed since the
formation of earth?
What forces have changed the
biodiversity on earth?
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Why is there life on Earth?
• The conditions on Earth are "just right" for life to exist.
• What conditions are important?
• Distance from sun + spin = Temperature is
just right (liquid water)
• Size = gravity to keep atmosphere, molten
core
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How did life come to exist on earth?
• Chemical evolution (1 billion years)
> Organic molecules and biopolymers
> *Cell membrane + genetic material!
> Evidence: radioactive elements in primitive rocks
and fossils.
> Miller and Urey famously attempted to replicate the
conditions of primitive earth to show by example
that life could form from the molecules and energy
available in the atmosphere and water.
Primitive
atmosphere:
Methane, ammonia,
hydrogen, water
http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/miller.html
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How did life come to exist on earth?
• Biological evolution (3.7 billion years)
> Single celled prokaryotes to multicellular organisms
> What process creates this diversity?
– Evolution by natural selection
> Evidence for biological evolution
– Fossil record
– Ice cores
– Chemical/DNA analysis
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Evolution by Natural Selection
• Wallace and Darwin
• In order for natural selection to occur, there must be:
> Variation amongst individuals in a population
> Variation must be heritable
– source of variation is mutation and must be in a
cell that is inherited by offspring
« caused by mutagens or mistakes during DNA
replication
> Traits must lead to differential reproduction
– More advantageous trait = more offspring. Over
time, the population changes so that this trait is
more prevalent
– adaptation or adaptive trait is any heritable
trait that allows an organism to survive and
reproduce.
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What other options are there?
• When environmental conditions change, a population
has 3 options
> adapt
> migrate
> become extinct
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Evolution by Natural Selection
• Important to remember:
> Natural selection happens at the individual level
> Evolution happens at the population level
http://evolution.berkeley.edu/evolibrary/article/evo_25
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Limitations to natural selection
1.
Gene pool limits a population's ability to adapt--you
can only select from traits you have. You can't create
new ones (except by chance through mutation).
2. Reproductive capacity can limit a population's ability
to adapt
> Organisms that reproduce rapidly (weeds, bacteria,
cockroaches, mice) adapt quickly
> Organisms that reproduce slowly (humans, whales,
tigers) take longer to adapt
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Misconception about Natural Selection
• Fitness does not mean strongest
> Fitness = reproductive success. Ability to
produce viable offspring.
• Organisms cannot develop traits because they need
them or want them.
> Genetic variation + natural selection makes
adaptive traits more common in a population.
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Other clarifications about evolution by natural
selection
• Evolution = changes in a population's genetic makeup
over time
> Over time = over generations
• Natural selection is one of the mechanisms for evolution
to occur. The other mechanisms include:
> Mutation
> Migration
> Genetic drift (population bottleneck and founder
effect)
> Horizontal gene transfer
> Hybridization
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Coevolution
• Textbook: "a biological arms race" between interacting
populations of different species.
• More broad description: Coevolution is when two or
more species reciprocally affect each other's evolution.
> Occurs when species interact closely with one
another
– predator/prey
– parasite/host
– competitive species
– mutualistic species
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Exampes of coevolution
Ants and Acacia--hollow thorns, secrete
nectar at base for ants. Ants protect
acacia against herbivores.
http://evolution.berkeley.edu/evosite/evo101/IIIFCoevolution.shtml
Yucca and Yucca moth--The
moth lays its eggs in the
flower, and the larvae feed on
the fruit. The moth pollinates
flowers.
This yucca moth is inside the flower of a yucca, Yucca glauca. Photo by Ann Cooper, BugGuide.net.
http://www.fs.fed.us/wildflowers/pollinators/
pollinator-of-the-month/yucca_moths.shtml
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Changes in the environment necessitates
adaptation by natural selection.
• Geologic processes
• Climate change
• Catastrophes
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Geologic Processes
• Tectonic plates
• Alfred Wegener
• The Earth's lithosphere is broken up into a series of
giant solid plates.
• These plates sit on the asthenosphere (a layer of
molten rock) and drift across the Earth's surface.
http://www.rsc.org/Education/Teachers/Resources/jesei/platerid/plates.htm
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Geologic Processes
• Effect on evolution:
1. Locations of continents and oceans influences earth's
climate -->distribution of animals and plants
2. Separation and joining of continents have allowed
species to move, adapt to new environments, and
form new species by natural selection.
3. Volcanic eruptions (at plate boundaries) destroys
habitats and reduce or wipe out populations. Opens
up habitat to be repopulated. Lava can yield fertile
soil (rich in nutrients like phosphorous and other
minerals)
4. Earthquakes can separate and isolate populations
(leads to speciation)
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Climate Change
• Repeated changes in earth's climate throughout
history.
• Alternating periods of cooling and heating
> Ice age and interglacial periods
> During interglacial periods-ice melts, sea level
rises, ice sheets retreat
http://geology.utah.gov/surveynotes/gladasked/gladice_ages.htm
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Climate Change
Effects on evolution:
1. Determines where plants/animals can live
(distribution)
2. Changes distribution of ecosystems--deserts,
grasslands, forests, etc.
3. Some species become extinct when climate change
occurs rapidly.
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Catastrophes
• Asteroids and meteorites collide with earth.
• Impact causes destruction of ecosystems and
extinction of species
Effects on evolution:
• 1) Long period of environmental stress--wipe out
species and habitat
• 2) Mass extinctions open up opportunities for new
species
Vredefort Crater, South Africa
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Ecological Niche
• Every species has a ecological niche, or a specific
role in the ecosystem.
> Where it lives/grows (habitat)
> Where it reproduces and how
> What it eats, how it eats.
> How it interacts with other species and
environment.
> "How an organism makes a living"
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Ecological Niche
• Fundamental niche - the full potential range of
physical, chemical, and biological conditions and
resources a species could theoretically use if it could
avoid competition from other species.
• Realized niche - the actual niche a species occupies.
Is only a part of the fundamental niche.
\\
Experiment by
Joseph Connell
Figure 53.13, page 1117, Campbell's Biology, 5th Edition
http://www.hammiverse.com/lectures/53/1.html
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Ecological Niche
Generalist species have broad niches.
• Can live in different places, eat many types of foods,
tolerate wide range of environmental conditions.
• Better able to survive changing environment.
Specialist species occupy narrow niches.
• Use only one/few types of food, tolerate narrow range
of environmental conditions.
• More prone to extinction due to change in environment
• Low competition when conditions constant
• Ex:
bam
hab
rat
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Specialist Species
• Specialist species can allow for resource
partitioning. Resource partitioning reduces
competition and allows sharing of limited resources.
• When different species compete for scarce resources,
natural selection results in more specialized species to
reduce competition
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Speciation
• Speciation: formation of new species, two species arise
from one.
> For sexually reproducing species-when some
members of a population can no longer breed with
other members to produce fertile offspring.
http://evolution.berkeley.edu/
evolibrary/article/0_0_0/evo_42
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Mechanism of Speciation
• Reproductive isolation is the key to speciation:
barriers to gene flow allow genetic differences to
accumulate and result in different species.
• Reproductive isolation may occur due to
> Different mating location, time, or rituals.
> Lack of "fit" between sexual organs.
> Offsprings not viable or fertile.
These damselfly penises illustrate just how complex insect genitalia may be
http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_44
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Mechanism of Speciation
• Why does reproductive isolation occur? Reduced gene
flow!
1) Allopatric speciation: Geographic Isolationmembers of the same population become physically
isolated. Adapt to different environmental conditions
> physical barriers (mountain range, stream, lake,
road)
> volcanic eruptions
> earthquake
> individuals taken away by wind or water
http://evolution.berkeley.edu/evosite/evo101/VC1bAllopatric.shtml
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Mechanism of Speciation
2) Peripatric speciation
A small number of individuals move into a new niche,
and by chance (think genetic drift), have genes that are
rare in the original population.
http://evolution.berkeley.edu/evosite/evo101/VC1cPeripatric.shtml
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Mechanism of Speciation
3) Parapatric speciation
• No extrinsic barrier to random mating, but population
mates non-randomly over a large geographic area.
• More likely to mate with others in same geographic
location within population.
Although continuously distributed, different
flowering times have begun to reduce gene flow
between metal-tolerant plants and metal-intolerant
plants.
http://evolution.berkeley.edu/evosite/evo101/VC1dParapatric.shtml
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Mechanism of Speciation
4) Sympatric speciation
• Does not require large-scale geographic distance
(physical isolation).
• Disruptive selection.
http://evolution.berkeley.edu/evosite/evo101/VC1eSympatric.shtml
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Mechanism of Speciation
• These mechanisms of speciation occur very slowly-over many years.
• There are other mechanisms of evolution that can
happen quickly (in one generation)
> 1) Hybridization: Two individuals of different
species are able to mate and produce viable
offspring. (often happens in plants by
polyploidy).
> 2) Horizontal gene transfer
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Sexual Reproduction is adaptive--maintains genetic
diversity in a population
• Genetic diversity is important to be able to adapt to
constantly changing and challenging environment.
• Remember traits are passed from parent to offspring
(vertical gene transfer)
Some microorganisms can
exchange genes without
sexual reproduction by
horizontal gene transfer
• Adaptations can occur
quickly--doesn't require
generations.
• Confounds phylogenetic
trees
http://www.nature.com/nrmicro/journal/v4/n1/fig_tab/nrmicro1325_F2.html
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Extinction
• Extinction: entire species ceases to exist.
• Species become extinct when populations cannot
adapt to changing environmental conditions.
• Endemic species = species that are only found in one
area. (Islands, small unique areas, highly specialized)
are especially vulnerable to extinction.
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All species eventually become extinct.
• background extinction: ongoing extinction of
species dues to changes in environmental conditions.
> Estimated to be about 1-5 species for each
million species on earth.
• mass extinction: widespread event of high
extinction rate. Large groups of existing species
(25-70%) are wiped out.
> Estimated there have been 5 mass extinctions
during past 500 million years.
• mass depletion: extinction rates higher than normal
but not high enough to be considered mass extinction.
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When a mass extinction or mass depletion occurs, gives
other species opportunity to fill previously occupied
niches or newly created ones.
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Biodiversity = speciation - extinction
• Why is biodiversity important for the ecosystem?
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Human Effects on Earth's Biodiversity
• Human activities are decreasing earth's biodiversity.
> As human population increases, resource
consumption increases.
> Humans take over more of earth's surface and net
primary productivity.
> Degrade or destroy habitats.
Do you remember the 5 ways in
which people are accelerating
species loss?
•
•
•
•
•
H: habita
I: invasi
P: Pollut
P: huma
O: Over
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Predictions by Stuart Primm and Edward O. Wilson (2005
Millenium Ecosystem Assessment)
• Extinction rates have increased 100-1,000 times natural
background extinction rates.
• By 2030: premature extinction of 1/5 earth's species.
• Can we recover from these major losses?
> Species formed over millions of years.
> Humans are depleting and destroying habitats with
in years.
> Need to protect! (strategies to be discussed in later
units)
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Artificial Selection and Genetic Engineering
• Artificial selection: Selective breeding, humans
breed certain animals or plants for certain desirable
traits.
> Relatively slow process: need to select
individuals, crossbreed, and repeat with offspring.
> Also limited to species that are related.
http://en.wikipedia.org/wiki/Selective_breeding
http://en.wikipedia.org/wiki/File:Cornselection.jpg
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Artificial Selection and Genetic Engineering
• Genetic engineering: alteration of an organism's
genetic material through adding, deleting, or changing
segments of its DNA to produce desirable traits or
eliminate negative ones.
> Recombinant DNA: DNA that has been altered
or contain genes or portions of genes from
organisms of different species.
> GMOs or transgenic organisms: organisms
that have been genetically engineered using
recombinant DNA
> Much faster than artificial selection, don't need to
breed so can transfer genes from unrelated
organisms.
September 30, 2014
Artificial Selection and Genetic Engineering
• Genetic engineering: alteration of an organism's
genetic material through adding, deleting, or changing
segments of its DNA to produce desirable traits or
eliminate negative ones.
> Biopharming: using genetically engineered
animals to act as biofactories for drugs, vaccines,
antibodies, hormones, chemicals, organs
• Synthetic biology: use fundamental components of
cells to rebuild new organisms
> Cloning
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How to make a transgenic organism
•
•
•
•
Identify gene of interest
Cut out and paste into a construct
Insert gene into organism of interest
Grow organism
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How to make a transgenic organism
•
•
•
•
Identify gene of interest
Cut out and paste into a construct
Insert gene into organism of interest
Grow organism
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How to make a transgenic organism
•
•
•
•
Identify gene of interest
Cut out and paste into a construct
Insert gene into organism of interest
Grow organism
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Get into groups of 3-4 and share your GMO's.
• Categorize your GMO's: you will present your categories
and what GMOs are in your categories.
• Make a list of the benefits and/or concerns about GMOs.
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Concerns About the Genetic Revolution
• Not a controlled, predictable process: trial and error
• Ethical issues (designer babies, selection of embryos,
genetic diseases/disorders)
• Socioeconomic distribution of technology and its
benefits.
• Consumer choice/information: Labeling of GMO's in food
labels
• Disrupt ecosystems (pesticides kill natural predator
insects)
• Accelerate genetic evolution (pesticide use)
• Exploitation of developing countries resources by
developed countries
• Food safety issues
• Contamination of normal crops
September 30, 2014