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Chapters 3-5
Communities,
Population Biology, Biological
Diversity & Conservation
Big Idea: How much can ecosystems
handle before we screw them up
permanently?
Living in the Community


Community – collection of
interacting populations
Limiting Factors –
environmental factors that
affect an organism’s ability
to survive in its environment



Can be living: food
availability, predators
Can be non-living:
temperature, water, sunlight
Can affect a population
directly or indirectly

For instance, food availability
will affect a herbivore and the
carnivore that eats the herbivore
Ranges of Tolerance

Tolerance – the ability of an organism to withstand
fluctuations in biotic and abiotic environmental
factors


Each organism has a specific range that it can survive in for
a specific factor
Ex: catfish can tolerate warm water with little oxygen,
while bass or trout cannot
Population
Organisms
Absent
Organisms
Infrequent
Zone of
Zone of
Physiological
Intolerance
stress
Low
Greatest Number of
Organisms
Pg. 66 of book
Organisms Organisms
Infrequent
Absent
Optimum Range
Zone of
Physiological Zone of
Stress
Intolerance
Range of Tolerance
High
Succession
Let’s say you no longer cut your lawn. What
would happen with sufficient water?
1. The grass gets taller; weeds start to grow. The
area resembles a meadow.
2. Later, bushes grow, trees appear and different
animals enter the area to live.
3. The bushes and trees change the environment;
less light reaches the ground. The grass slowly
disappears.
4. Thirty years later, the area is a forest.

Succession

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The orderly, natural changes and species
replacements that take place in the
communities of an ecosystem
Primary Succession – the colonization of
new sites by communities of organisms
Pioneer Species – the first species in an
area




Ex: Lichen (a combination of fungus and algae)
grows readily after a volcanic eruption
Lichens break up rock slowly and help soil
accumulate
Slowly, more things are able to live in the
environment
Climax Community – mature community
that undergoes little or no change

Ex: Deciduous forest
Secondary Succession

The sequence of community
changes that takes place after a
community is disrupted by natural
disasters or human actions



Occurs on land that already has soil
The pioneer species will be different
and the community will climax in a
shorter time
Example: Yellowstone burned in
1988

Wildflowers came back first, then
grasses, ferns and pine seedlings
Biome



A biome is a large group of ecosystems that share
the same type of climax community
There are terrestrial biomes (tundra, taiga, desert,
grassland, temperate forest, rain forest)
There are aquatic biomes (marine, estuaries,
freshwater)
Review
1.
2.
3.
4.
5.
6.
What are the two kinds of limiting factors?
What is a range of tolerance? Give an
example.
What is primary succession?
What is secondary succession?
What is a biome?
What is a pioneer species?
Chapter 4 – Population Biology


Population Growth – an
increase in the size of a
population over time
All populations start off
growing relatively
slowly (relative to their
capacity to reproduce)
If resources are not
limited, all populations
will grow exponentially
(a “J” curve)
Exponential Growth
250
200
Number

150
E. coli
100
50
0
1 2 3 4 5 6 7 8 9 10
Time
Realistic Population Growth



Resources are never unlimited
Populations will reach a carrying capacity – the
number of organisms of one species that an
environment can support
Populations follow an S-shaped growth curve
Pg. 94 of book
Carrying Capacity – if
population gets bigger,
organisms die
Carrying Capacity
---------------------------------------------------------------------------------------------------
Beginning
Growth Population
slowly
increases
Leveling Off –
competition,
limited resources
slow growth,
limiting factors
Rapid Growth –
exponential growth
Fluctuations –
birth and death
rates fluctuate
with competition
and resources
Patterns of Population Growth

Some organisms reach
their carrying capacity
faster than others


Environmental Conditions


This is due to their
reproductive patterns
Ideal ranges
In general, organisms that
are small and mature
rapidly reach carrying
capacity faster

Organisms that are large and
mature slowly, reach a
carrying capacity slower
Environmental Limits to
Population Growth

Density-Dependent Limiting Factors have an
increasing effect as the population increases

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
Ex: disease, competition, parasites, food
Ex: How does predation effect population sizes?
Density-Independent Limiting Factors affect
all populations, regardless of their density

Most are abiotic factors such as temperature,
storms, flood, drought, habitat destruction
Density-Dependent Limiting Factors

Competition – increases within species as population
gets too big.
 Over food, water, territory, mates, etc.
 Can you see this in a human population?
Density-Dependent Limiting Factors

Crowding & Stress – as
populations increase in
size, individual animals
begin to exhibit:
 Aggression
 Decrease in parental
care
 Decreased fertility
 Decreased
resistance to disease
 Can you see this in
a human
population?
Review
1.
2.
3.
4.
5.
6.
What conditions must be met for exponential
growth?
What pattern do populations follow in reality?
What determines how fast a population reaches its
carrying capacity?
Give 3 density-independent limiting factors.
How can crowding and stress limit a population?
Describe the relationship between predators and
prey.
Demographic Trends

Demography – the study of human population growth
characteristics

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Humans reduce negative environmental effects on our
population

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i.e., growth rate, age structure, geographic distribution
i.e., eliminating competitors, increasing food production,
controlling diseases
Human Population (see pg. 100 in book)
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1 A.D. – around 1850 : slow growth
After 1850-present: exponential growth (J-curve)
Realistic Population Growth
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
Where are humans on this curve?
What will eventually have to happen?
Pg. 94 of book
Carrying Capacity – if
population gets bigger,
organisms die
Carrying Capacity
---------------------------------------------------------------------------------------------------
Beginning
Growth Population
slowly
increases
Leveling Off –
competition,
limited resources
slow growth
Rapid Growth –
exponential growth
Fluctuations –
birth and death
rates fluctuate
with competition
and resources
Birth and Death Rates

Death Rate – the number of deaths per 1000 people in a given year
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
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Affected by life expectancy, diseases in area, stress, etc.
Difference in Africa and U.S.?
Birth Rate – the number of live births per 1000 people people in a
given year.


Fertility rate is a large influence here
Difference in Africa and U.S.?
Birthrate (per
1000)
Death Rate (per
1000)
Fertility (per
woman)
Population
Increase (percent)
Jordan
38.8
5.5
3.3
3.3
Uganda
50.8
21.8
7.1
2.9
Zimbabwe
34.3
9.4
5.2
2.5
Germany
9.4
10.8
1.2
-1.5
Italy
9.4
9.7
1.2
-0.5
Sweden
10.8
10.6
1.5
0.1
Mexico
27.0
5.2
3.1
2.2
United States
14.8
8.8
2.0
0.6
Population Growth Rate (PGR)
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Immigration – movement of individuals into a
population
Emigration – movement from a population
Population Growth Rate = (Birthrate + Immigration
Rate) - (Death Rate + Emigration Rate)
Or, for convenience

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PGR = Birthrate - Death rate
When birthrate equals death rate, the population isn’t
growing
As long as the PGR is positive, the population will
continue to grow
Doubling Time & Age Structure

Doubling Time - the time needed for a population to
double in size
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Age structure refers to the proportions of a population
that are at different age levels
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Doubling Time (in years) = 70/annual percent growth rate
What is happening to the world doubling time?
If a population has many young members, it will mostly
likely grow rapidly
If a population has equal numbers of ages, it is stable
Look page 103 in book
These demographics do not influence world
population, but do show movement from or to urban
areas, countries, etc.
Ecology and Growth
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Population needs differ throughout
the world
Some populations have competition
for food, water, etc.
Some population are more concerned
about the health of their citizens
When populations grow rapidly,
there is often competition for
resources

Lead to stress, contamination, etc. that
lead to disease and affect stability of
populations
Review
1.
2.
3.
4.
5.
How do humans “change the rules” in
demography?
How do birth rates and death rates influence
population growth?
How do you calculate population growth
rate?
What is a population’s doubling time?
How do population needs differ around the
world?
Biological Diversity

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Biodiversity refers to the variety of life in an area
 Most common measure is the number of species that live in a
certain area
Terrestrial biodiversity tends to increase as you move towards the
equator (or in isolated warm regions)
 2/3 of all land species on Earth are in tropical regions
The size of the area also affects biodiversity
 Larger areas tend to be more diverse (unless other things
prevent or encourage life)
Importance of Biodiversity

Organisms are adapted to live together in a
community

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Biodiversity brings stability to an ecosystem

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If you take one away, there are consequences to the rest
More resources, interactions, etc.
When a population utilizes more than one resource, it will
be ok if one of them disappear
Biodiversity is important to humans

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Oxygen to breath, remove CO2
Diverse diet / Better crops (resistance)
Building materials
Possible pharmaceuticals
Loss of Biodiversity

Extinction – the disappearance of a
species when the last of its members
dies

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Threatened Species – when the
population of a species begins declining
rapidly


Since 1980, almost 40 species of plants and animals
have gone extinct in the U.S.
Can be natural or human-caused
In the US: sea otters, loggerhead turtles, bald eagle
Endangered Species – population
numbers so low that extinction is
possible

In the US: California Condor, Florida manatees
Threats to Biodiversity
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Habitat loss – the biggest threat
 Take away resources for life
Habitat fragmentation – separation of wilderness areas from
other wilderness areas
 Roads – leads to less biodiversity
 Animals that migrate or need large areas to hunt
 Climates can change (take away shade)
 Edge Effect – the different conditions along the
boundaries of an ecosystem
Threats to Biodiversity

Habitat Degradation – the damage to a habitat by
pollution

Air, Water, or Land

Air Pollution

Burning fossil fuels is the greatest source of air
pollution
Acid Precipitation – sulfur dioxide from burning
coal and nitrogen oxides from automobile exhausts
combine with water vapor
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Leaches nutrients from the soil
Damages plant tissues
Alters pH of lakes
Ozone layer damage – CFC’s break down 03

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Increased skin cancers
Possible cause for amphibian population decreasing
Threats to Biodiversity
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Water Pollution
Fertilizers and animal wastes carried by runoff
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Causes algal blooms
These algae die, decay and remove oxygen from the water
Silt from erosion clogs gills, blocks sunlight
Detergents, metals, industrial chemicals from runoff
Debris in oceans and lakes
Threats to Biodiversity
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Land pollution
Trash – the average American produces about
1.8 kg of solid waste daily – 657 kg/yr

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Destroy habitats and pollute areas
Pesticides, etc. can also lead to habitat
degredation

DDT
Threats to Biodiversity
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Introduction of Exotics
Exotic species – organisms that are
not native to a particular area
 Can grow at an exponential rate
due to a lack of competitors and
a lack of predators
 Take over niches of native
species or replace the
species
 Sea lamprey in Great
Lakes after Erie Canal
 Goats on Santa Catalina
Island
Section 1 Review
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What are two reasons for a species to become
threatened or endangered?
Explain how land that gets broken up can contribute
to loss of species diversity.
What is an edge effect? Explain how changes in an
ecosystem’s edges can affect organisms.
How can exotic species affect populations of native
species?
Conservation Biology

Conservation Biology is the
study and implementation of
methods to protect biodiversity.

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Natural resource conservation natural resources are those parts
of the environment that
are useful or necessary
for living organisms.
Species conservation protecting species from
extinction and preserving
biodiversity
Legal Protection of Species

1973, the U.S. Endangered Species Act made it
illegal to harm any species on the endangered or
threatened list
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Illegal for federal agencies to
fund any project that would
harm these species
The Convention on International Trade in Endangered
Species (CITES)
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Established lists of species for which international trade is
prohibited or controlled
Honored by 120 countries
Preserving Habitats

One way is to create
national parks
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First one in US was
Yellowstone
Originally this was to
preserve the geology
Protects natural
environments and
provides habitats
for many organisms
Habitat Corridors

Protected strips of land
that allow the migration
of organisms from one
wilderness to another

Isolated populations
inbreed too much
Sustainable Use

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In National Parks, the land is managed
This philosophy strives to enable people to use
natural resources in ways that will benefit
them and maintain the ecosystem

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Some grazing
Harvest fruits
Hiking, camping, etc.
Preservation Programs

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Captive Breeding followed by
Reintroduction Programs
 Release organisms into
area where the species once
lived
 Ex: black-footed ferret
 Ex: brown pelican after
DDT
Seed banks for threatened and
endangered plant species
Section 2 Review
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Describe the U.S. Endangered Species Act.
Why is it difficult to reintroduce species that
have been captive bred?
What is sustainable use and how does it
influence Utah?