Download Chap 5 APES

Ch 5
Evolution, Biodiversity, and
Population Ecology
Part 1: Foundations of
Environmental Science
PowerPoint® Slides prepared by
Jay Withgott and Heidi Marcum
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2008 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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
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Early Earth was a very different place
Theory- dispersed bits of material whirling through space around our sun
were drawn together by gravity
• 4.5 billion years ago, Earth was a hostile place
- Severe volcanic and tectonic activity
- Intense ultraviolet energy from the sun
- No oxygen existed in the atmosphere, until
photosynthesis developed in microbes
- No life existed
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Several hypotheses explain life’s origin
• Primordial soup (the heterotrophic hypothesis) life originated from a “primordial soup” of simple
inorganic chemicals in the oceans
- First life forms used organic compounds for energy
• “Seeds” from space (the panspermia hypothesis) microbes from space traveled on meteorites to Earth
• Life from the depths (the chemoautotrophic
hypothesis) - life originated in deep-sea hydrothermal
vents, with abundant sulfur
- First organisms were chemoautrotrophs
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The fossil record teaches about life’s history
• Single-celled bacteria occurred
on Earth 3 billion years ago
• Fossil - an imprint in stone of a
dead organism
• Fossil record - gives
information about the history of
past life
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Present-day organisms help decipher
• Biologists use present-day
history
organisms to get information
about evolution
• Archea - single-celled
prokaryotes very different from
bacteria
• The tree of life now consists of
3 prongs: bacteria, archaea,
eukaryotes
• Prokaryote- a typically
unicellular organism that lacks
organelles and nucleus
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Evolution: the source of Earth’s biodiversity
• Biological evolution - genetic change in
populations of organisms across generations
- 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
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Understanding evolution is vital
• 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
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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
- Organisms tend to produce more offspring than
can survive
- 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
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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
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Natural selection acts on genetic variation
• Directional selection - drives a
feature in one direction (a-thick
shell protects snail)
• Stabilizing selection - produces
intermediate traits, preserving
the status quo (b-preserves extra
resources for feeding and reproduction
an favors an int. shell)
• Disruptive selection - traits
diverge in two or more
directions (c- two traits are favored.
Thin shells conserve resources and out
reproduce and thick shells are well
protected)
If the environment changes, a trait may no longer be adaptive
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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
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Natural selection
• Selective breeding has produced tremendous diversity
among organisms
• Adaptive radiation- burst of species formation due to
natural selection
Statistics
1.5 to 1.8 million species have been discovered
Estimated 100 million species mat exist
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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, and agricultural crops
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Evolution generates biodiversity
• Biological Diversity - An area’s sum total of all
organisms
- The diversity of species
- Their genes
- Their populations
- Their 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
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Speciation produces new types of organisms
• The process of generating new species
- A single species can generate
multiple species
• Allopatric speciation - species
formation due to physical separation
of populations over some geographic
distance
• DNA mutation arises in the isolated
population
- Can be separated by glaciers,
rivers, mountains, migration
- The main mode of species creation
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Genetic Drift
occurs when changes in the frequency of a gene in a
population are due not to mutation, selection or
migration but simply to chance
Founder Effect (allopatric)
- occurs when a small number of individuals are
isolated from a larger population
- They may have a smaller genetic variation than the
original species
Both genetic drift and founder effect may not be better
adapted to their environment
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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
- Hybridization between two species
- Mutations
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The fossil record shows that…
• Earlier organisms evolved into later ones
• The vast majority of species are extinct
• Numbers of species increase over time
• Earlier organisms were smaller and simpler
• Several mass extinctions have occurred
• Large, complex organisms occurred 600 million years
ago
- Plants, animals, fungi
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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
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Extinction
• Species generally evolve from
simple to complex and small to big,
but the opposite can occur, and
some even disappear
• 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
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Extinction is a natural process
• Extinction is irreversible: once a species is lost, it is
lost forever
• Humans profoundly affect rates of extinction
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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 (golden toad to the Monteverde cloud forest)
- Very susceptible to extinction
- These species usually have small populations
• Many other factors also cause extinction
- Severe weather
- New species
- Specialized species
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Earth has had several mass extinctions
• Background extinction rate –the average rate of
extinction that occurred before the appearance of
humans
• Fossil record indicates that for both bird and
mammals one species in the world typically becomes
extinct every 500-1000 years or
• One to five species per million species on earth
extinction usually occurs one species at a time
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Extinction
• Mass extinction events – a catastrophic widespread
event where large groups of species are wiped out in a
geological period lasting up to 5 million years
• five events in Earth’s history that killed off massive
numbers of species at once (20-60 million years apart
during the past 500 million years)
• 250 million years ago, 50-95% of all species went extinct
at one time
• Humans are causing the sixth mass extinction event
- Resource depletion
- Population growth
- Development
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Causes of Extinction
• Risk- the chance that a species of population will become
extinct owing to one of these causes
1- Population Risk- random variations in population rates
(in birth rates and death rates) can cause a species low in
abundance to become extinct (butterfly in Colorado
mountains only lay their eggs in the buds of a lupine tree.
Their was a late snow killing all the buds)
2- Environmental Risk- changes in the environment that
occur. This includes variations in the physical and
biological environment
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Causes of Extinction – cont.
3- Natural
Catastrophe- sudden changes in the
environment that is not a result of human
activities (volcano, earthquake, flood)
4- Genetic Risk- changes in genetic characteristics,
not caused by external environmental changes
(species lacks variety and may be vulnerable)
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Species’ ranges can be severely restricted
Some U.S. salamander species live on top of single mountains
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Endangered Species- Red List
• The International Union for Conservation of Nature (IUCN) is
the world's main authority on the conservation status of species.
A series of Regional Red Lists are produced by countries or
organizations, which assess the risk of extinction to species
•
The percentage of species in several groups which are listed as red critically endangered,
orange endangered, or yellow vulnerable on the 2007 IUCN Red List
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
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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
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Organismal ecology: habitat
• Habitat - the environment in which an organism lives
- Includes living and nonliving elements
- Scale-dependent: from square meters to miles
- each organism thrives in certain habitats, but not in
others (habitat use)
• 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
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Organismal ecology: niche
• Niche - an organism’s use of resources and its
functional role in a community
- total way of life or role of a species in an
ecosystem
- 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
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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
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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 dynamics – the study of how the
characteristics of the population change in response to
changes in the environmental conditions
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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
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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
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Birth and death rates
• Crude birth/death rates rates per 1000 individuals
• 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
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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
• Growth rate formula -
- (Crude birth rate + immigration rate) - (Crude death
rate + emigration rate) - Growth rate
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Exponential population growth
• Steady growth rates cause
exponential population
growth
- Something increases by a
fixed percent
- Graphed as a J-shaped
curve
• Exponential growth cannot be
sustained indefinitely
- It occurs in nature with a
small population and ideal
conditions
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Limiting factors restrain growth
Intrinsic rate of increase (r) is the rate at
which the population of a species would
grow if it had unlimited resources
- Reproduce early in life
- Have short generation times
- can reproduce many times and have many
offspring
• Limiting factors - physical, chemical and
biological characteristics that restrain
population growth
- Water, space, food, predators, and disease
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Carrying capacity
• Carrying capacity (K)the maximum population
size of a species that its
environment can sustain
- An S-shaped logistic
growth curve
- Limiting factors slow
and stop exponential
growth
• Carrying capacity changes
Humans have raised their carrying capacity by decreasing the
carrying capacity for other species
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Perfect logistic curves aren’t often found
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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
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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
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K-selected vs. r-selected species
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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
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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
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Preserving biodiversity
• Natural parks and protected areas help preserve
biodiversity
- Often, they are underfunded
- Ecotourism brings jobs and money to developing
areas
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