Download A Closer Look at Natural Selection…

We’ve already learned through example and models why
biodiversity is important. Let’s define the various types of
biodiversity, however, since there are many:
The most commonly thought of biodiversity, and that is
• Species Diversity simply defined as the species “richness” or the variety of
species in an area.
This refers to the variety of defined ecosystems within an
• Ecosystem diversity area, such as deserts, grasslands, forests, and such. It
also refers to the number of communities and populations
in an area as well.
• Functional diversity Refers to the variety of processes such as matter and
energy cycling that is accomplished in ecosystems on
Earth. (including nutrient cycles and food webs)
• Genetic diversity Refers to the variety of genes within a species, which dictate
the characteristics of the organisms that possess them…and
Refers to the variety of human cultures, and attributes of
• Cultural diversity human cultures which help humans adapt to changing
conditions.
• Supplies us with food, wood, fibers, medicines, and energy
• Preserving the quality of our water and air
• Maintaining the fertility of the soils
• Disposal of wastes
• Control populations of pests
Kingdom Plantae, 250,000
species
We’ve already spent a good deal of time evaluating the
Protista…250,000
importanceKingdom
of
biodiversity.
Let’s remind ourselves exactly
species
what biodiversity is…
Kingdom
• The variety of the Earth’s species, the genes
they contain,
Animalia,
1,000,000
the ecosystems in which they live, and the
ecosystem
species
processes such as energy flow and nutrient cycling that
sustain all life.
fly agarics
mushroom
Kingdoms Eubacteria, and
Kingdom
Archaebacteria…10,500 speciesFungi,
50,000
far, scientists
species
So
have identified 1.8
million of Earth’s 4100 million species.
So…just where did all these
organisms come from, and how did
this biodiversity happen?
There are few things in science that are as controversial as the
origins of life, but the fact is that however it started, it has
persisted on Earth for nearly 3.8 billion years!
As scientists speculate that the first life on Earth was Prokaryotic…just how did such
diversification occur?
The work done in the 1800s by Charles Darwin, and Alfred Wallace helped to
explain how this all happened.
• There is a struggle for existence
(competition for resources) in populations
that contain many variations.
• Those that outcompete others in a
population, survive and pass those traits that
helped them, along to their offspring
• Those that compete unsuccessfully, die and
don’t pass their traits along.
• Over time, advantageous traits are selected
for naturally…
Complex Multicellular Heterotrophs which is why we call this process… Natural
Selection
Current Stromatolites
Fossil Stromatolites
A Closer Look at Natural Selection…
• Similar organism reproduce similar organisms. A dog
reproduces a dog, and a dandelion reproduces a
dandelion.
• Often, the number of offspring is overproduced: The
number that survive is less than that initially reproduced.
• Individual organisms must compete with each other and
with other species for limited resources in the
environment (food, water, space, mates…etc)
• In any population, individuals vary with respect to any
given trait (height, skin color patterns, size, speed)
• Some variations are favorable (make those individuals
more likely to be successful at reproduction, than those
with unfavorable traits)
• Those organisms with favorable traits will survive and
pass those traits on to their offspring. Those with
unfavorable traits will die and not pass on their traits
(NATURAL SELECTION)
• Given sufficient time, because natural selection will
accumulate these favorable traits, the species will change
or evolve.
Stromatolites: A record of the oldest life on Earth…
Most of what we know about prehistoric life comes from fossilized evidence of its
existence. Fossils are mineralized or petrified replicas of skeletons, bones, teeth, shells,
leaves, seeds…or even impressions left by such items and preserved in rock.
The fossil record is
incomplete. Why?
Teleoceras: Fossilized Rhino
Some animals don’t
leave fossils behind.
Still others have
been destroyed by
the rock cycle.
Fossil Stromatolites
The work of piecing together evidence of past life from fossils is done by the
Paleontologist
How do species evolve?
The environment in which an organism lives determines
what traits or variations are favorable
• Genetic Drift
Slight random changes in the genetic makeup of a
population over time
This genetic variability is created by chance mutations in genes of organisms, while
DNA is replicating.
• Natural Selection
Some of these “errors” can occur when the
cells are exposed to agents that cause
mutations…called “mutagens”….such as UV
radiation.
While mutations can occur in any cell
in the body (somatic), it is the
mutations that occur in the sex cells
that enable those mutations to be
passed on to the next generation.
I hope
this
molecule
looks
familiar!
What characteristics have allowed humans to dominate Earth the
way they have?
 Opposable Thumb
 Walking Upright
 Complex Brain
While humans are not by any
means excluded from the
chances of extinction, our
brains may indeed be our most
advantageous adaptation…to
help us find ways to cope with
the changes in the environment
(which we are largely causing)
that most organisms would find
intolerable, and impossible to
adapt to.
Will humans be able to adapt to future environmental probabilities? Probably because…
 Nature will only select advantageous traits that already exist in a population, or
that are likely to be created by mutations.
 Even if that trait is present, reproductive capacity
may hold back the evolutionary tendency
Organisms with very
short life cycles are
far more capable of
producing the
variations necessary
for rapid evolution, as
opposed to those who
only produce 1-4
offspring during their
lifetimes
The Earth today looks nothing like it
did when it formed, and it continues
to change dramatically every day.
Earth’s molten mantle, which lies
beneath the crust, is constantly
moving the hardened plates
around through convection
currents.
This becomes important as to the
placement of organisms, because
where oceans and land are
located greatly influences
environmental conditions.
When these plates carrying the continents separate and/or fuse together, new
environmental conditions arise, setting up new circumstances for organisms. This gives
them the opportunity to adapt, migrate, or become extinct. 
Throughout Earth’s Geologic History, the environments have
changed greatly.
• Hot and dry at the end of the Permian
• Snowball Earth (Proterozoic Eon)
• High oxygen
• High CO2
• Meteorite
impacts
A high degree of
genetic biodiversity
allowed life to
continue on this
planet that is
constantly changing!
Gorgonopsid in Permian Desert
When natural selection leads to an entirely new species, a
process called “speciation” has occurred. Speciation can occur in
a number of ways:
 A species may become Geographically Isolated
Any time a population of
organisms becomes
“isolated” they have the
chance to “diverge” from
the other population.
Places on Earth that
have been “isolated” for
long periods of time,
have developed really
diverse and “unique”
species.
 A Species is Reproductively Isolated
Occurs when something acts to prevent organisms from
reproducing together, and is usually driven by the
females of a species.
A natural process which affects the levels of biodiversity on Earth
is extinction. Extinction occurs when the last surviving individual
of a species is gone.
Determining the exact moment of extinction is difficult, and is often
determined retrospectively. Sometimes the reproductive potential
of a species ceases before the last individual actually dies.
Every day about 137 species
become extinct. That’s over
50,000 species every year!
The most vulnerable species
are “endemics”, who are only
found in one area.
• Amphibians
Coqui
Blue Poison Dart Frog of Surinam
Takahe in New Zealand
Panamanian golden frog
The fossil record indicates that a low rate extinction (or
background extinction) occurs when one to five species becomes
extinct for each million or so species on Earth…whereas a Mass
Extinction occurs when there is a significant rise above
background level.
Mass extinctions occur when
global catastrophic events
cause large groups of species
(25-70%) to be wiped out, in a
geological period lasting up to
5 million years.
Mass extinction periods also are marked
by low speciation rates as well.
The one plus that occurs during periods of mass extinction is that
it gives new species the opportunity to fill the habitats and niches
left by the now extinct organisms.
Each species in an ecosystem
plays a role, also known as an
A niche can be anything from dietary needs
“ecological niche”.
of organisms, temperature needs, or
Niche is not to be
amount of daylight, or darkness that they
confused with habitat,
need. A niche may also include mating and
which is where an
reproductive patterns
organism lives.
Niches are used to
help define species
as either
“generalists” or
“specialists”.
Roaches, the great generalists
The narrower the niche, the more prone to extinction a species is.
Native species are those which are
indigenous, or that normally live in
an ecosystem.
Indicator species are those which are
used as a “gauge” by ecologists to
determine the health, or degree of
ecological danger in an ecosystem.
Giant Swallowtail Butterfly
American Elm in Fort Worth
Lichens
Tree of Heaven
Nonnatives are also known as
invasive, or exotic species
North American Bison
Remove the keystone, and the arch tumbles
Black-Tailed Prairie Dogs
Just as keystones are the
most important factor that
hold arches together,
keystone species have a
great affect on the types
and abundance of other
species in an ecosystem.
Many keystone species
are prone to extinction
because of small
populations, which leads
to a cascade effect.
Foundation species
actually “build”
Bald and golden eagles, swift foxes, coyotes,
ferruginous hawks, burrowing owls, badgers and ecosystems, literally
black-footed ferrets, countless insects and other providing the
invertebrates, as well as plants also rely on
“foundation” for the
Prairie Dogs and their activities.
community.
Each of you will produce a three-slide PowerPoint/Prezi/ or some other multi-media
presentation…to be uploaded to NetSchool. Each person will become an expert on one
extinct, and one endangered organism, and be prepared to discuss and answer
questions after their presentations. Each person’s presentation must have imported
graphics/pictures/animation, and:
Slide One:
Highlight one species that has become extinct on Earth (with picture)
 When?
Why…what were the circumstances?
What niche did they fill in their ecosystem?
What was their habitat like?
Were they keystone species, or foundation? Etc…
Slide Two:
Tell how the extinction of that species impacted/affected/ caused a cascade
effect in their ecosystem, or impacted at least two other organisms
 Slide Three:
Choose an endangered species, and predict what would happen in their
ecosystem if they were to become extinct.