Ecology
Part 4. Populations
Part 5. Communities
Part 6. Biodiversity and Conservation
Population Ecology: Population Growth Models
Population Limiting Factors
• Population growth models
– Logistic Growth Model
• Often called the S-shaped growth curve
• Occurs when a population’s growth slows or stops
following exponential growth.
• Growth stops at the population’s carrying capacity
• Populations stop increasing when:
– Birth rate is less than death rate
(Birth rate Immigration)
Population Ecology: Population Growth Models
Population Limiting Factors
• Population growth models
– Logistic Growth Model
The S-curve is not as pretty as the image looks
1. Carrying capacity can be raised or lowered. How?
Example 1: Artificial fertilizers have raised k
Example 2: Decreased habitat can lower k
2. Populations don’t reach k as smoothly as in the logistic
graph.
• Boom-and-Bust Cycles
• Predator-Prey Cycles
Community Ecology: Communities
Communities
• Review:
– A community is a group of interacting populations
that occupy the same area at the same time.
Community Ecology: Communities
Communities
• Limiting Factors
– Any abiotic or biotic factor that restricts the
numbers, reproduction, or distribution of
organisms.
Community Ecology: Communities
Communities
• Range of Tolerance
– The limits within which an organism can exist.
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession
– The change in an ecosystem that happens when
one community replaces another as a result of
changing biotic and abiotic factors
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession
– Consists of 2 types:
• Primary Succession
• Secondary Succession
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The establishment of a community in an area of
exposed rock that does not have topsoil is called
Primary Succession.
• It occurs very slowly at first
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The first organisms to arrive are usually lichens or
mosses, which are called pioneer species.
• They secrete acids that can break down rock
• Their dead, decaying organic materials, along with bits
of sediment from the rock make up soil.
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– Small weedy plants and other organisms become
established.
– As these organisms die, additional soil is created
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– Seeds brought in by animals, water and wind
begin to grow in the soil.
– Eventually enough soil is present for shrubs and
trees to grow.
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession
• Ecological Succession: Primary
– The stable, mature community that eventually
develops from bare rock
is called a
climax community.
Community Ecology: Ecological Succession: Secondary Succession
Ecological Succession
• Ecological Succession: Secondary
– Disturbances (fire, flood, windstorms) can disrupt
a community.
– After a disturbance,
new species of plants
and animals might
occupy the habitat.
Community Ecology: Ecological Succession: Secondary Succession
Ecological Succession
• Ecological Succession: Secondary
– Pioneer species in secondary succession are
usually plants that begin to grow in the disturbed
area.
– This is much faster
than primary
succession
Community Ecology: Ecological Succession
Ecological Succession
• Ecological Succession: End point?
– Cannot be predicted
– Different rates of growth &
human involvement
make it impossible to
know if a true climax
community has been
reached.
Biodiversity and Conservation: Introduction
On the left side of your IntNB,
address the following:
• What would happen if all of the jackrabbits in
a food web died suddenly?
• Is the disappearance of one species from
Earth important, or will another species fill its
niche?
Biodiversity and Conservation: What is biodiversity?
Biodiversity
• What is Biodiversity?
The variety of life in an area that is
determined by the number of different
species in that area.
• There are 2 main types:
Genetic Diversity Species Diversity
Biodiversity and Conservation: Why is biodiversity important?
Biodiversity
Penicillin: Derived from
bread mold
Teosinte: A Domestic corn
distant relative plant
of corn
Madagascar Periwinkle: Used to
treat childhood forms of leukemia
Biodiversity and Conservation: Extinctions
Extinction Rates
• The gradual process of becoming extinct is
known as background extinction.
• Mass extinctions: When a large percentage of
all living species become extinct in a relatively
short period of time.
• 250 MYA: Over
90% of species
died
Biodiversity and Conservation: Extinctions
Estimated number of Extinctions since
1600
Group Main- Island Ocean Total Approximate Percent of
land Number of Group
Species Extinct
Mammals 30 51 4 85 4000 2.1
Birds 21 92 0 113 9000 1.3
Reptiles 1 20 0 21 6300 0.3
Amphibians 2 0 0 2 4200 0.05
Fish 22 1 0 23 19,100 0.1
Invertebrates 49 48 1 98 1,000,000+ 0.01
Flowering 245 139 0 384 250,000 0.2
Plants
Biodiversity and Conservation: Extinctions
Five Most Recent Mass Extinctions
Cretaceous Period (65 MYA)
Triassic Period (200 MYA)
Permian Period (250 MYA)
Devonian Period (360 MYA)
Ordovician Period (444 MYA)
Activity: Understanding Geological
Time
• Working in your groups, you will get the
following supplies:
– A meter stick
– A roll of 5 meters of paper
– Colored pencils
• Using the worksheet, plot out the dates.
– 1 million years is a millimeter
– 1 billion years is a meter