Transcript PPT File

Chapter 5
Evolution of Biodiversity
Biodiversity is a key indicator of
environmental health
• Biodiversity is critical to our survival. We
depend on it for almost everything: food, fuel,
clothing, building materials and medicines to
name but a few. Biodiversity is also very
important to our quality of life.
• The number of species in any given place is
the most common measure of biodiversity.
• The insect group contains more species than
most other groups
The total number of Insects species is
estimated to be over 30 million!
Species Richness vs Species Eveness
Species Richness
Species Evenness
The number of species in a
given area
The relative proportions of individuals within
the different species
Indicates the approximate
sense of the biodiversity of
a particular place
Indicates whether a particular ecosystem is
dominated by one species or whether all
species have similar abundance
Can help scientists evaluate Can help scientists evaluate impact of a
impact of a disturbance
disturbance
Both species richness and evenness can be measured using the ShannonWeiner Index of Biodiversity.
Phylogenetic tree
Phylogenetic trees show how
different groups of organisms are
related and show where
speciation occurred.
Evolution is the mechanism underlying
biodiversity
• Microevolution- evolution below the species
level (varieties of different apples or potatoes)
• Macroevolution- genetic changes gives rise to
new species(speciation), genera, families, classes
or phyla
• Genetic diversity is created by mutation(random
change in the genetic code which can be caused
by UV radiation from the sun) and
recombination(when part of a chromosome
breaks off and attaches to another chromosome
during replication and can produce novel traits.
Evolution by different processes
Artificial Selection
Natural Selection
Random Processes
Humans determine which
individual breed with a
preconceived set of traits in mind
Ex: Labradoodle
The environment determines
which individuals survive and
reproduce
Ex: Survival of the Fittest
The genetic composition of a
population still changes over time,
but the changes are not related to
differences in the fitness among
individuals.
Most of our agricultural crops are
the result of careful breeding
Theory developed by Darwin in
1859-Individuals produce an
excess of offspring, not all
offspring can survive, individuals
differ in their traits, differences in
traits can be passed on from
parents to offspring, differences in
traits are associated with
differences in the ability to survive
and reproduce.
Examples: Mutation, Genetic
Drift( change in the genetic
composition of a population over
time as a result of random
mating), Bottleneck effect(a
reduction in genetic diversity of a
population caused by a reduction
in population size), Founder effect
(a change in population
descended from a small amount
of colonizing individuals)
Has led to unwanted results:
resistant strains
And other unintended results
Natural selection favors any
combination of traits that
improves an individual
Speciation and extinction determine Biodiversity
Allopatric vs Sympatric Speciation
• Allopatric Speciation: when geographic isolation(separating a
population by a geographic barrier change)creates new
species . When this occurs eventually the populations from
the older area and the newer area can no longer breed and
are in reproductive isolation. The 2 populations become 2
distinct species. This is the most common way evolution
generates new species.*
• Sympatric Speciation: the evolution of one species into two
species in the absence of geographic isolation, usually
through a process called polyploidy (the number of
chromosomes increases to multiple sets instead of the usual
diploid number, accidently or with human intervention). Once
polyploid, these organisms can no longer breed with diploid
ancestors and become reproductively isolated.**
Allopatric Populations
• Allopatric speciation is just a fancy name for
speciation by geographic isolation. In this mode
of speciation, something extrinsic to the
organisms prevents two or more groups from
mating with each other regularly, eventually
causing that lineage to speciate. Isolation might
occur because of great distance or a physical
barrier, such as a desert or river.
Sympatric Populations
• In Sympatric Speciation the separation is nongeographical but more "behavioral" or "social".
This form of speciation is believed to be
particularly significant in the evolution of insect
species.
• Ex: Many herbivorous insects lay their eggs on a
particular plant variety so that when the larvae
hatch they have a readily available food supply.
Mating may also take place on the same plants.
The larvae become imprinted with this plant and
when they reach adulthood they in turn will lay
their eggs on the same plant.
• If an adult makes a mistake and lays its eggs
on the wrong plant, all subsequent
generations will become imprinted with the
same wrong plant. This behavioral-related
separation results in the insects on the
"wrong" plants being separated from the
original group so that over time speciation
occur.
http://www.youtube.com/watch?v=n3265bno2X0&list=UUm
5KJSPhpKJdmPUrrYFHgng&index=1&feature=plcp
The Pace of Evolution
• A significant change in a species genotype and
phenotype can take anywhere from hundreds
to millions of years.
• Average global rate of evolution is about one
new specie every 3 million years.
• The ability of a specie to survive an
environmental change depends greatly on
how quickly it evolves the adaptations needed
to thrive and reproduce under the new
conditions.
To survive a rapid environmental change, a population must
evolve adaptations quickly or go extinct. Successful adaptation
depends on 4 factors:
• Rate of environmental change: if it happens too quickly, most
species do not have time to adapt and will go extinct
• Genetic Variation: High levels of genetic variation ensures
that some individuals will be well suited to the new
environment and allows for more rapid evolution by natural
selection.
• Population size: if a small population experiences a mutation,
it can spread more quickly because the individual with the
mutation will breed with a number of mates that represent a
large proportion of the entire population.
• Generation time: If the time between generations is small,
the change in genetic composition of a species, occurs more
quickly.
Genetic Engineering
• Evolution occurs even more rapidly in
populations of genetically modified organisms.
• Scientists can insert genes with desirable traits
into organisms w/o them to produce
genetically modified organisms.
• These organisms will pass on the new traits to
their offspring.
• Obviously this is much quicker than traditional
plant breeding which can only select from the
naturally available variations in a population.
Evolution shapes ecological niches and
determines species distributions
• The fundamental niche of a species is the ideal
range of abiotic conditions such as temperature,
humidity, salinity, and pH under which members
can survive, grow and reproduce). As conditions
move away from the ideal, individual may be able
to survive but not grow or reproduce.
• The addition of biotic factors more narrowly
defines the parts of the fundamental niche that a
species actually use. The range of abiotic and
biotic conditions which a species actually lives is a
realized niche.
Fundamental and Realized Niche
• Some species live under a very wide range of
abiotic and biotic conditions(niche generalists)
while others can live under a very narrow range
(niche specialists).
• Niche specialists are vulnerable to extinction if
conditions change.
• Changes in environmental conditions have led to
distribution changes in species in the past. We
can predict with an increase in global
temperatures, this pattern will continue.
• Some species can move physically more quickly
than others to adapt to these climatic changes
and shift their distribution pattern
Distribution model of the yellow
throated vireo
This specie can live under a wide variety of conditions.
Environmental changes and Species Extinctions
• If environmental conditions change and species cannot move
or adapt, they go extinct.
• 99% of species that have ever lived on earth are now extinct.
• Throughout Earth’s history , the fossil record indicates there
have been 5 periods of global mass extinction.
• The greatest mass extinction occurred 251 million years ago.
90% of marine and 70% of land vertebrates went extinct.
• 65 million years ago (end of the Cretaceous period) the
dinosaurs went extinct along with 50% of earth’s species.
• Scientists think we are experiencing another mass extinction
now and during the last 2 decades as a result of habitat
destruction, over harvesting, climate changes and emerging
diseases.
Fossils Data shows 5 Prior mass
extinctions
Diversity of Marine Animals and
Extinction
Sea level drops and mass extinction