Transcript Chapter5- Evolution, Biodiversity, and Population

Ch 5
Evolution, Biodiversity, and
Population Ecology
Part 1: Foundations of
Environmental Science
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
This lecture will help you understand:
• Natural selection
• How evolution influences
biodiversity
• Reasons for species
extinction
• Ecological organization
• Population
characteristics
• Population ecology
• Conservation biology
Striking gold in Costa Rica
• Golden toads were
discovered in 1964, in
Monteverde, Chile
• The mountainous cloud
forest has a perfect
climate for amphibians
• Unfortunately, they
became extinct within
25 years
- Due to global
warming’s drying
effect on the forest
Striking gold in Costa Rica
“I must confess that my initial
response when I saw them
was one of disbelief and
suspicion that someone had
dipped the examples in
enamel paint.”
-Dr. Jay M. Savage,
Describing the Golden Toad in 1966
“What a terrible feeling to
realize that within my own
lifetime, a species of such
unusual beauty, one that I
had discovered, should
disappear from our planet.”
-Dr. Jay M. Savage,
Describing the Golden Toad in 1998
Evolution: the source of Earth’s biodiversity
• Biological evolution  genetic change in
populations of organisms across
generations (change over time)
• May be random or directed by natural
selection
- Natural Selection  the process by
which traits that enhance survival
and reproduction are passed on more
frequently to future generations
than those that do not
Understanding evolution is vital
WHY should we understand / learn
about evolution?
• It alters the genetic makeup of a population
• It is important for understanding antibiotic
and pesticide resistance, agricultural issues,
production, medicines, etc.
• Organisms adapt to their environment and
change over time
Natural selection shapes organisms
•
In 1858, Darwin and Wallace both proposed
natural selection as the mechanism of evolution
-
Organisms face a constant struggle to survive
and reproduce (Struggle for Existence)
-
Individuals of a species vary in their
characteristics due to genes and the
environment
-
Some individuals are better suited to their
environment and will survive and pass their
genes on in their offspring (Survival of the
Fittest)
-
Organisms evolved from common ancestor with
changes over time (Descent with Modification)
What’s with those tail feathers?
Genetic variation
• Adaptive Trait (Adaptation)  a trait that
promotes reproductive success
• Mutations  accidental changes in DNA that may be
passed on to the next generation
- Non-lethal mutations provide the genetic variation
on which natural selection acts
• Sexual reproduction also leads to variation
Natural selection acts on genetic variation
Directional selection
drives a feature in one
direction
Stabilizing selection
produces intermediate
traits, preserving the
status quo
Disruptive selection
traits diverge in two or
more directions
If the environment changes, a trait may no longer be adaptive!!
Natural selection acts on genetic variation
Evidence of natural selection is everywhere
• It is evident in
every adaptation of
every organism
• Evident in bacteria
and fruit flies in
laboratories
• Selective breeding
of animals
Artificial selection
• Artificial Selection  the process of
selection conducted under human direction
- For example, artificial selection has led to
the great variety of dog breeds
Artificial selection
Evolution generates biodiversity
• Biological Diversity  An area’s sum total of all
organisms
- Diversity of species, their genes, populations,
and communities
• Species  a population or group of populations
whose members share characteristics and can
freely breed with one another and produce
fertile offspring
• Population  a group of individuals of a species
that live in the same area
Speciation produces new organisms
• Speciation  process of
generating new species
- A single species can
generate multiple species
• Allopatric speciation 
species formation due to
physical separation of
populations
- Can be separated by
glaciers, rivers, mountains
- The main mode of species
creation
DARWIN’S
FINCHES
Allopatric speciation
Another type of speciation
• Sympatric speciation 
species form from
populations that become
reproductively isolated
within the same area
- Feed in different areas,
mate in different
seasons
- Mutations
Speciation results in diverse life forms
• Speciation generates complex patterns of diversity
above the species level
• Phylogenetic trees (Cladograms)  Represents the
history of species divergence
- Scientists can trace when certain traits evolved
- Show relationships between species
Extinction
the disappearance of a species from Earth
- Occurs when a species
cannot adapt quickly
enough to a changing
environment
- Speciation and extinction
affect species numbers
Extinction is a natural process
• Extinction is irreversible: once a species is
lost, it is lost forever!!!!!
• HUMANS profoundly affect rates of
extinction (overhunting, destroy habitats, etc.)
Some species are more vulnerable to extinction
• Extinction occurs when the environment changes too
rapidly for natural selection to keep up
• Endemic species  a species only exists in a certain,
specialized area (EXAMPLE??)
- Very susceptible to extinction … WHY???
- These species usually have small populations
• Many other factors also cause extinction
- Severe weather
- New species
- Specialized species
Earth has had several mass extinctions
• Background extinction rate  extinction usually
occurs one species at a time
• Mass extinction events  five events in Earth’s
history that killed off massive numbers of
species at once (MOST COMMON?)
- 50-95% of all species went extinct at one time
• Humans are causing the sixth mass extinction
event
- Resource depletion
- Population growth
- Development
Species’ ranges can be severely restricted
Some U.S. salamander species live on top of single
mountains … VULNERABLE TO EXTINCTION!
Ecology is studied at several levels
• Ecology and evolution are
tightly intertwined
• Biosphere  the total
living things on Earth and
the areas they inhabit
• Ecosystem 
communities and the
nonliving material and
forces they interact with
• Community  interacting
species that live in the
same area
Levels of ecological organization
• Population ecology = investigates the quantitative
dynamics of how individuals within a species
interact
• Community ecology = focuses on interactions
among species
• Ecosystem ecology = studies living and nonliving
components of systems to reveal patterns
- Nutrient and energy flows
Organismal ecology: habitat
• Habitat  the environment in which an organism lives
- Includes living and nonliving elements
• Habitat use  each organism thrives in certain
habitats, but not in others
• Habitat selection  the process by which organisms
actively select habitats in which to live
- Availability and quality of habitat are crucial to an
organism’s well-being
- Human developments conflict with this process
Organismal ecology: niche
• Niche  an organism’s use of resources and its
functional role in a community
- Habitat use, food selection, role in energy and
nutrient flow
- Interactions with other individuals
• Specialists  species with narrow niches and very
specific requirements
- Extremely good at what they do, but vulnerable to
change
• Generalists  species with broad niches that can use
a wide array of habitats and resources
- Able to live in many different places
Population characteristics
• All populations show
characteristics that
help scientists predict
their future dynamics
• Population size  the
number of individual
organisms present at a
given time
- Numbers can
increase, decrease,
cycle or remain the
same
Population characteristics
• Population density  the number of individuals
within a population per unit area
- High densities make it easier to find mates,
but increase competition, and vulnerability to
predation
- Low densities make it harder to find mates,
but individuals enjoy plentiful resources and
space
Population characteristics
• Population distribution
(dispersion)  spatial
arrangement of organisms
within an area
- Random: haphazardly
located individuals, with no
pattern
- Uniform: individuals are
evenly spaced due to
territoriality
- Clumped : arranged
according to availability of
resources
- Most common in nature
Population characteristics
• Sex ratio = proportion of males to females
- In monogamous species, a 50/50 sex ratio
maximizes population growth
• Age Structure = the relative numbers of organisms
of each age within a population
- Age structure diagrams (pyramids) = show the age
structure of populations
Birth and death rates
• Survivorship curves  the
likelihood of death varies
with age
- Type I: More deaths at
older ages
- Type II: Equal number
of deaths at all ages
- Type III: More deaths
at young ages
Four factors of population change
• Natality  births within the population
• Mortality  deaths within the population
• Immigration  arrival of individuals from outside
the population
• Emigration  departure of individuals from the
population
Why would individuals move in or out of an area?
Exponential population growth
• Steady growth rates cause
exponential population
growth
- Graphed as a J-shaped
curve
• Exponential growth cannot
be sustained indefinitely
- It occurs in nature with a
small population and
IDEAL conditions
Exponential population growth
UNLIMITED RESOURCES!!!
Exponential Growth
Logistic population growth
• Growth that is limited
and levels off is logistic
population growth
- Graphed as a Sshaped curve
• More likely to occur in
nature but not often
- Takes into account
that resources are
limited in nature
Carrying capacity
• Carrying capacity 
the maximum population
size of a species that
its environment can
sustain
- Certain factors slow
and stop exponential
growth
• Carrying capacity
changes
Humans have raised their carrying capacity by
decreasing the carrying capacity for other species
Perfect logistic curves aren’t often found
Limiting factors restrain growth
• Limiting factors  physical, chemical
and biological characteristics that
restrain population growth (cause
decline)
- Competition for resources, predation,
parasitism, disease, weather, and
human disturbances
Population density affects limiting factors
• Density-dependent factors  limiting factors
whose influence is affected by population density
- Increased risk of predation and competition for
mates occurs with increased density
• Density-independent factors  limiting factors
whose influence is NOT affected by population
density
- Events such as floods, fires, and landslides
Population density affects limiting factors
Biotic potential and reproductive strategies vary
• Biotic potential  the ability of an organism to
produce offspring
• K-selected species  animals with long gestation
periods and few offspring
- Have a low biotic potential
- Stabilize at or near carrying capacity
- Good competitors
• r-selected species  animals which reproduce
quickly
- Have a high biotic potential
- Little parental care
K-selected vs. r-selected species
Population changes affect communities
• As population in one species declines, other
species may appear
• Human development now displaces other species
and threatens biodiversity
- As Monteverde dried out, species from lower,
drier habitats appeared
- But, species from the cloud-forest habitats
disappeared
Challenges to protecting biodiversity
• Social and economic factors affect species and
communities
- Nature is viewed as an obstacle to
development
- Nature is viewed as only a source of
resources
- Human population growth pressures
biodiversity
Preserving biodiversity
• Natural parks and protected areas help
preserve biodiversity
- Often, they are underfunded
- Ecotourism brings jobs and money to
developing areas
QUESTION: Review
Which of the following is NOT a part of the
process of natural selection?
a) Organisms struggle to survive
b) Organisms limit the number of young they
produce
c) Individuals vary in their genetic
characteristics
d) Some individuals are better suited to their
environment than others
QUESTION: Review
Disruptive selection would result in which of the
following?
a) Dogs with black coats evolving whiter coats in
colder areas
b) Red and white flowers interbreeding,
producing pink flowers
c) Fish evolving bigger eyes as the water gets
muddier
d) A population of birds, some with thicker
beaks that eat seeds and others with thinner
beaks that eat insects
QUESTION: Review
Biological diversity includes all of the following, except:
a) Species diversity
b) Genetic diversity
c) Population diversity
d) Community diversity
e) All of these are included in the concept of
biodiversity
QUESTION: Review
Sympatric speciation would occur in ....
a) One population that mates in May, and
another that mates in June
b) Two populations separated by the
Mississippi River
c) Two populations separated by a glacier
d) Two populations separated by the Rocky
Mountains
QUESTION: Review
Which of these species is least vulnerable to
extinction?
a) A species with a population size of 50
individuals
b) A species distributed throughout the
United States
c) A species that eats only river snails
d) A species that lives on mountaintops
QUESTION: Review
An ecosystem is defined as:
a) The total living things on Earth
b) Members of the same population that can interbreed
c) Interacting species in an area
d) Species and the nonliving material they interact
with
QUESTION: Viewpoints
Should we care whether a species goes extinct?
a) Yes, because all life is important and
valuable
b) Yes, because we are causing this wave of
extinction, so we should fix it
c) We should not, because it’s natural
d) I don’t care; it really does not affect me
QUESTION: Viewpoints
Do you think humans are subject to limiting factors and,
ultimately, a fixed carrying capacity?
a) Yes, although we have raised the carrying capacity,
there are limits to the number of humans the Earth
can support
b) Yes, but technology will keep raising the carrying
capacity, so it’s not much of a problem
c) No, humans are no longer constrained by
environmental limits, due to our technology and
ability to manipulate the environment
d) I don’t care; it really does not affect me
QUESTION: Interpreting Graphs and Data
Which of the following graphs shows a population
that will have fewer individuals in the future?
(a)
(b)
(c)
(d)
QUESTION: Interpreting Graphs and Data
Which type of distribution
is a result of individuals
guarding their territory?
a) Random
b) Uniform
c) Clumped
d) None of these
QUESTION: Interpreting Graphs and Data
What does this graph show?
a) The effects of
carrying
capacity on
population
growth
b) A population
that keeps
growing
c) The effects of
exponential
growth
d) The effects of