Ecology
Part 4. Populations
Part 5. Communities
Part 6. Biodiversity and Conservation
Population Ecology: Population Characteristics
Population Characteristics
1. Population Density:
–
The number of organisms per unit area
2. Spatial Distribution:
–
–
Dispersion: The pattern of spacing a population
within an area
3 main types of dispersion
•
•
•
–
Clumped
Uniform
Random
The primary cause of
dispersion is resource
availability
Population Ecology: Population Characteristics
Population Limiting Factors
3. Population growth rate
– How fast a given population grows
– Factors that influence this are:
•
•
•
•
Natality (____
birth rate)
death rate)
Mortality (_____
Emigration (the number of individuals moving
_________
away from a population)
moving to a
Immigration (the number of individuals _________
population)
Population Ecology: Density-independent factors
Population Limiting Factors
• Density-independent factors
– Factors that limit population size, regardless of
population density.
– These are usually abiotic factors
– They include natural phenomena, such as weather
events
• Drought, flooding, extreme
heat or cold, tornadoes,
hurricanes, fires, etc.
Population Ecology: Density-dependent factors
Population Limiting Factors
• Density-dependent factors
– Any factor in the environment that depends on
the number of members in a population per unit
area
– Usually biotic factors
– These include
•
•
•
•
Predation
Disease
Parasites
Competition
Population Ecology: Population Growth Rate
Understanding Exponentials
• Put your pens down for a minute & think about
this:
– An employer offers you two equal jobs for one hour
each day for fourteen days.
– The first pays $10 an hour.
– The second pays only 1 cent a day, but the rate
doubles each day.
– Which job will you accept?
Population Ecology: Population Growth Rate
Understanding Exponentials
Job 1
90
80
70
60
50
40
30
20
10
0
Job 2
Now, how much would
your employer owe you
if you stayed at this job
for another 2 weeks?
Job 2 lags for a long
time before
exponential growth
kicks in!
1
2
3
4
5
What would happen if this
type of growth took place
within a population?
6
7
8
9
10 11 12 13 14
Population Ecology: Population Growth Rate
What population do you think this is?
What letter
does this
curve
resemble?
The USCB estimates that the world population exceeded 7
billion on March 12, 2012
• Population growth models
– Exponential growth model
• Also called geometric
growth or J-shaped growth.
• First growth phase is slow
and called the lag phase
• Second growth phase is rapid
and called the exponential
growth phase
• Bacteria can grow at this
rate, so why aren’t we up to
our ears in bacterial cells?
Population Limiting Factors
• Population growth models
– Limits to exponential growth
• Population Density (the number of individuals per unit
of land area or water volume) increases as well
• Competition follows as nutrients and resources are
used up
• The limit to population size that a particular
environment can support is called carrying
capacity (k)
So, what do you think is going to
happen to the human population?
• We will probably reach our carrying capacity.
• Our growth rate will start to look like most
organisms, which is the Logistic Growth Model
http://en.wikipedia.org/
wiki/Overpopulation
Carrying Capacity (k)
What letter does this curve
kind of look like?
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 < Death rate)
– Emigration exceeds Immigration
(Emigration > 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
r and K strategists
• A logistic equation can describe the self-limiting growth of a
biological population.
• where r is the maximum growth rate of the population (N),
and K is the carrying capacity of its local environmental
setting, d stands for derivative, and t for time.
In r/K selection theory, selective pressures drive evolution
in one of two generalized directions: r- or K-selection
r and K strategists
Traits that are thought to be
characteristic of r-selection include:
•high fecundity
•small body size
•early maturity onset
•short generation time
•ability to disperse offspring widely
Evolved to take advantage in
unstable environment, density
independent
Traits that are thought to be
characteristic of K-selection include:
large body size
•long life expectancy
•production of fewer offspring
•extensive parental care until they
mature
Evolved to take advantage in stable
environment, density dependent
interactions
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.
Name
some…
Community Ecology: Communities
Communities
• Range of Tolerance
– The limits within which an organism can exist.
Think: Effects of global
warming/climate
change?
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:
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; dispersal
– 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
• 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?
“Keystone” species
…is a species that has a disproportionately
large effect on its environment relative to
its abundance.
• Play a critical role in maintaining the
structure of an ecological community
• Affect many other organisms in an
ecosystem
Examples:
1) Pacific Coast: purple sea urchin can damage kelp
forests by chewing through kelp holdfasts
The sea otter is an important predator of sea urchins.
2) Grey wolves in Yellowstone
3) Can you think of any other examples?
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 distant
relative of corn
Domestic corn plant
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.
• Ex: 250 MYA: Over
90% of species
died
Biodiversity and Conservation: Extinctions
Estimated number of Extinctions since
1600
Group
Mainland
Island
Ocean
Total
Approximate
Number of
Species
Percent of
Group
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
Plants
245
139
0
384
250,000
0.2
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