Download Chapter 5 Evolution of Biodiversity

Chapter 5
Evolution of Biodiversity
Earth is home to a tremendous
diversity of species
• Ecosystem diversity- the
variety of ecosystems
within a given region.
• Species diversity- the
variety of species in a
given ecosystem.
• Genetic diversity- the
variety of genes within a
given species.
• Species richness- the number of species in
a given area.
• Species evenness- the measure of whether
a particular ecosystem is numerically
dominated by one species or are all
represented by similar numbers of
individuals.
How do we measure
biodiversity?
The Shannon-Weiner
Diversity Index
Evolution is the mechanism underlying
biodiversity
Evolution is the mechanism
underlying biodiversity
• Evolution- a change in the
genetic composition of a
population over time.
Macroevolution
• Macroevolution- Evolution
which gives rise to new
species or new genera,
family, class or phyla.
• Microevolution- evolution
below the species level.
(different varieties of same species)
Microevolution
Macroevolution
• Divergent Evolution- is a
mechanism of
macroevolution.
• It is the accumulation of
differences between groups which
can lead to the formation of new
species, usually a result of
diffusion of the same species to
different and isolated
environments which blocks the
gene flow among the distinct
populations allowing
differentiated fixation of
characteristics
Microevolution - Creating Genetic Diversity
• Genes- physical
locations of DNA on
chromosomes within
each cell of an
organism.
• Genotype- the complete
set of genes in an
individual.
• Mutation- a random
change in the genetic
code.
• Phenotype- the actual
set of traits expressed in
an individual. (what it
looks like)
3 Primary Ways in which Evolution Occurs
1.
Evolution by artificial
selection- when humans determine
which individuals breed. (example:
breeding dogs)
2.
Evolution by natural selection-
3.
Evolution by random
processes –these mechanisms change
the environment determines which
individuals are most likely to survive
and reproduce. (example: Darwin’s finches)
a population’s composition but are not
related to differences in fitness amount
individuals. (example: migration of
butterflies)
#1 Artificial Selection
Farmers and breeders were using
the idea of selection to cause major
changes in the features of their
plants and animals over the course
of decades.
This process is called artificial
selection because people (instead
of nature) select which organisms
get to reproduce.
#2 – Natural Selection
• Charles Darwin - After visiting
the Galapagos Islands, Darwin
wondered how so many species of
finches could have “descended
with modifications” from one
ancestral species.
• He came up with the theory of
natural selection to explain decent
with modification (environmental
survival of the fittest)
• A trait that makes an individual
successful in its environment is
called an adaptation
Darwin’s theory of evolution
by natural selection – 5 Points
1.
2.
3.
4.
5.
Population has variations.
(different traits)
Some variations are favorable.
More offspring are produced
than survive.
Those that survive will have
favorable traits
Those favorable traits are
passed on genetically from
generation to generation,
causing the population to
change over time.
Types of Natural Selection
What happens when there is a change to an environment?
• Stabilizing selection- favors
average individuals; reduces
variation in a population
• Disruptive selection- favors
both extreme variations of a
trait, resulting in no
intermediate forms of the trait
and leading to the evolution of
2 new species.
• Directional selection- favors
one of the extreme variations of
a trait and can lead to rapid
evolution of a population
#3. Evolution by Random Processes – 5 Types
#1 – Mutation
Changes in
DNA occur
randomly and
can add to the
genetic variation
of a population.
•Mutations add
genetic variation to a
population,
increasing genetic
diversity.
Evolution by Random Processes – 5 Types
#2 - Gene Flow
The process by
which individuals
move from one
population to
another and
thereby alter the
genetic
composition of
both populations.
Animals: immigration & emigration
• Gene flow can be
helpful in bringing
genetic variation to a
population that lacks
it.
Plants: pollination & seed dispersal
Evolution by Random Processes – 5 Types
• #3 - Genetic drift
Change in the
genetic composition
of a population over
time as a result of
random mating.
• Genetic drift has a
particularly significant
effect on the genetic
compositions of small
populations. Random
mating among
individuals with rare
genotypes can cause
elimination of that species
simply because they did
not find a mate in a given
year.
Evolution by Random Processes – 5 Types
#4 - Bottleneck Effect a
dramatic reduction in
population size is
caused by an
environmental issue,
which in turn reduces
the genetic diversity of
that population.
• Environmental issues
include habitat loss,
natural disasters,
harvesting by humans
or environmental
changes.
Evolution by Random Processes – 5 Types
#5 - Founder Effect
a change in the genetic
composition of a
population as a result
of descending from a
small number of
colonizing
individuals.
•Because individuals may not
bring all of the diversity of the
mainland, the island
population may have less
diversity.
Speciation & Extinction
Determines Biodiversity
Speciation - How New Species Evolve
• The process of species
formation is called
speciation
• Speciation begins with
isolation (organisms that
formerly interbred, no
longer can do so)
• There are 2 types of
isolations:
• Geographic Isolation
• Reproductive Isolation
Speciation - How New Species Evolve
• #1. Geographic Isolation – species are separated by
some physical barrier – such as mountain or river

Allopatric speciation is the
result of geographic isolation.
 Allopatric
means “different
homelands”.
 So Allopatric Speciation means
that when the original species
was separated into two, gene
flow stopped between them.
 The now two populations may
begin to differ due to genetic
drift, mutations and natural
selection.
Speciation - How New Species Evolve
• #2. Reproductive Isolation – Sometimes organisms
within a population will become genetically isolated,
without being geographically isolated. These organisms
simply cannot successfully mate. This can lead to a new
species being formed.
 Sympatric speciation is
the result of reproductive
isolation.
 usually
through the
process of polyploidy, an
increase in the number or
sets of chromosomes being
“turned on” or “turned
off”.
Allopatric vs Sympatric Speciation
Allopatric Speciation – due to Geographic Isolation when a barrier is
present
Sympatric Speciation – due to Reproduction Isolation when a barrier is
not present


The Pace of Evolution
(a) Environmental Change
A slow changing environment gives species more
time to adapt to the changes.
(b) Genetic Variation
Less genetic variation means there is less chance for
the species to adapt to changing conditions
(c) Population Size
If a beneficial mutation occurs, it can spread
more rapidly in a small population than in a
large population.
(d) Generation Time
Shorter generation times increase the chance that
beneficial mutation will occur within a given
amount of time and allow them to spread
throughout a population faster.
The Five Global Mass Extinctions
• What happens when an species can not
survive environmental change –
extinction!
• Mass extinction- when large numbers of
species went extinct over a relatively
short period of time.
In the worst
one, 250 million
years ago, 96% of
marine species
and 70% of land
species died off. It
took millions of
years to recover.
Asteroid
Impact
Higher Level of
Solar radiation
Sea Level
Fluctuations
Volcanic
Eruptions
Climate Change
(Ice Age)
The Sixth Mass Extinction
• Scientists feel that we
are in our sixth mass
extinction, occurring in
the last two decades.
• Estimates of extinction
rates vary widely, from
2 % to 25% by 2020.
• In contrast to previous
mass extinctions,
scientists agree that
this one is caused by
humans.
Extinction – three factors that make it difficult for
a population to survive environmental change:
• 1. Slow generation
time (population can’t
evolve rapidly enough)
• 2. Low genetic
diversity (natural
selection doesn’t work)
• 3. Environmental
degradation (no suitable
habitat to move to)
Ecological Habitats & Niches
determine Biodiversity
Habitat
• A habitat is the place where
an organism lives. A
habitat will include both
biotic and abiotic things.
(examples: backyard, parking lot,
wilderness, mountains)
Niche
• The specific way and
location where an organism
“makes a living” to stay
alive. (examples: what it eats, what
it does, where is lives)
Niche Defined
• Range of tolerance- all
species have an
optimal environment
in which it performs
well. The limit to the
abiotic conditions
they can tolerate is
known as the range of
tolerance.
Niche Defined
• Each species in an ecosystem has a specific role or
way of life.
• Fundamental niche: the full potential range of
physical, chemical, and biological conditions and
resources a species could theoretically use.
• Realized niche: to survive and avoid competition, a
species usually occupies only part of its fundamental
niche.
Notice that the Chthamalus has a large fundamental niche, but a small realized niche.
Probably due to competition with Balanus.
Niche Specialization
• Niches become
separated to avoid
competition for
resources.
Resource Partitioning
• Resource
partitioning
reduces
competition
and allows
sharing of
limited
resources in
niches.
Niches Defined
• Niche generalist-
species that live
under a wide
range of
conditions and
eats a variety of
foods.
• Niche specialistspecies that live
only in specific
habitats.
Which one is better? It depends…
• Koalas are super-specialists. Over the past few million
years they’ve managed to evolve the capability to eat and
metabolize poisonous eucalyptus leaves. This is great for the
koalas because it ensures a stable food supply. When it
comes to finding lunch, koalas have very little competition.
There aren’t many other animals out there who’d be able to
steal from the koala’s dinner plate. They’d die if they even
tried.
• The crow, on the other hand. Is an example of the supergeneralist. Crows will eat anything: fruit, meat, vegetables,
worms, garbage–even small animals. Anything they can get
their beak around, they’ll eat it. Crows, generalists as they
are, don’t have it as easy as the Koalas do. After all, they
have to compete with all the other birds, rodents, and
scavengers for a day’s sustenance. For them, day to day life
is a never-ending ordeal of hunting and foraging for scraps.
• But what would happen to the Koalas if the eucalyptus
trees are dramatically reduced?
• What would happen to the Crows if fruit trees didn’t
grow?