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Ecology. Biology 30. Ecology. Study of Ecosystems Abiotic & Biotic factors interacting Biotic Factors include populations & communities. Population Same species Same place Same time. Community Groups of pops interacting. Same species: Same place: Same time!.

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Biology 30


  • Study of Ecosystems

  • Abiotic & Biotic factors interacting

  • Biotic Factors include populations & communities

  • Population

  • Same species

  • Same place

  • Same time

  • Community

  • Groups of pops

  • interacting

Same species: Same place: Same time!

Can you explain the difference between a population and a community?

  • The definition for a population?

  • The definition for a community?

Biotic and Abiotic Factors?

Abiotic factors are the non-living components of an ecosystem

Biotic factors are the living components of an ecosystem

Can you tell me…

  • The difference between abiotic and biotic factors in an ecosystem?

  • An example of an abiotic factor?

  • An example of a biotic factor?

Ecosystem Community

or Population?



  • Why is the picture in the previous slide an example of a community and not an example of a population?


  • Variables we will consider:

    • Geographic Range

    • Habitat

    • Ecological Niche

    • Population Distribution

    • Population Size

    • Population Density

    • Population Growth Rate and Patterns

Geographic Range

  • area where animal has been seen

Fire Ant Range

Geographic range can change over time

due to abiotic factors.

Range Changes in Moose Populations

How has the geographic range of moose

changed since the 1870’s??


  • area where the population lives

  • where environmental conditions are best for survival

  • How does an organism’s geographic range differ from its habitat?

Ecological Niche

  • Role of the species in the community

  • Includes ALL biotic and abiotic factors a species needs to survive

Each group has a different role to

minimize competition

Populations co-exist only if each group occupies a different niche

  • Explain the meaning of the term ecological niche.

Population Distribution



Population Distribution

  • Determined largely by habitat preference

  • Divided into three patterns:

    1. Clumped - individuals grouped in patches due to certain environmental factors (e.x. trees clump on south slopes of river valleys b/c less direct sunlight and sturdier soils)

  • 2. Random

    • - not very common

    • - biotic and abiotic factors have little effect

3. Uniform

  • competition among individuals for resources results in regular spacing

  • What is the difference between clumped, random and uniform population distribution?

  • What factors are responsible for creating clumped, random and uniform population distributions?

Population Size

  • Number of organisms of same type in same place, at same time

  • There are 2000 students at CentreHigh during the 2004/5 school year.

  • Can be determined by exact count or estimation!!






Population Density

  • Describes number of organisms in a defined area

  • eg. Snow geese at Beaver Hills =

    # of geese per hectare

  • Density (D) calculated by dividing total number (N) by amount of space occupied (S) by the population

  • What is the difference between population size and population density?


D =



Density Example

There are 80000 snow geese in

a 50 hectare area in 1995.

D = N/S

= 1600 snow geese per ha

  • If 200 lemmings are living in a 25 hectare (ha) area of tundra, what is the population density of this area?

    • Use the formula D = N/S






Growth Rate

  • After finding the population density, we can find the rate of change over time

Change in number

Change in time

Rate of growth



Density Change example

  • In 1993, the mouse population in my backyard was 50 mice/acre. After three years, various control measures had been in place, and the population dropped to 10 mice/acre. Calculate the rate of density change.

50 - 10






  • When arriving at their summer cabin, the Smiths discovered 10,000 cockroaches roaming throughout their 1000 m2 cabin. After 1 week, the exterminators were able to control the situation and reduced the cockroach population to 10 per 1000 m2. Calculate the rate of density change.

Population Growth

  • Determined by four factors:

    • Natality

    • Mortality

    • Immigration

    • Emmigration



Population Growth



+ emmigration)

(births +


Initial # of organisms

Also known

as per capita

growth rate











  • Using this table, calculate CGR for Sandhill cranes:

Original Pop = 200








40 - 55


= -0.075

  • Puffins are small marine birds found off the coast of Atlantic Canada. Calculate the population growth rate of a puffin colony based on the following population in 1999.

    Original population = 200 000

    Natality = 15 000

    Mortality = 10 000

    Immigration = 175 000

    Emigration = 160 000

Density Problem

Calculate the population density of shrews per m2, if an average of 7.8 shrews are found in an area 14 m wide by 20 m.

CGR Calculation




Calculate the per capita growth rate of a mouse population if the original population size is 34 and over a period of a week, 5 die, 8 are born, 12 immigrate into and 7 emigrate out of the area.

Dynamic Equilibrium

  • Present in mature ecosystems

  • Characterized by long term balance

  • Pops remain relatively stable over time

  • Great biodiversity = stability

  • Can be compared with homeostasis

  • Define dynamic equilibrium.

2 population types:

1. Open populations:

  • immigration & emigration occurs

    2. Closed populations:

  • Density changes are result of natality and mortality only

  • No immigration or emigration

  • eg. Game preserves

  • What is the difference between open and closed populations?

Growth Curve

  • Graph showing changes in a population over time.

  • X = time (independent or manipulated variable)

  • Y = density or # of organisms (dependent or responding variable)

Exponential Pop Growth

Growth Curve for Closed System

  • 4 phases:

  • 1. Lag phase…slow…not enough

    reproducing organisms

  • 2. Growth phase….exponential increase

  • 3. Stationary phase….natality= mortality

  • 4. Death phase…decline

    • Not always present

Bacterial Growth Curve

Closed population

4 distinct phases

  • Draw a growth curve for a closed population. Label and define the four stages of this curve.

Growth Curve for Open Systems

  • When a limiting factor is introduced to a population, curve results in an “S” shape

    • Typical of an organism placed in a new environment

  • As organisms respond to increased nutrients, natalityincreases.

    • Equilibrium is established again and curve levels off

  • New carrying capacity (max. # of individuals environment can support)

  • Define carrying capacity.

  • When does a population growth curve of an open system show an “S shape”?

Population Growth Curves

  • Click on the link above

  • Read the instructions and hit the “run applet” button

  • Set the carrying capacity to 1000

  • Set the birth rate to 1.5

  • Hit RUN

  • View the graph and draw this in your notes

  • Have you simulated an open or a closed population?

  • Change the parameters and try it again!

Population Curves

Human Population Growth

Population Curves

Population Curves

  • How could you describe the population growth of humans in the past 500 years?

    • Hint: one word that begins with an ‘e’

Population Explosion & Crashes


What happened?

  • Describe the bottleneck effect.

Boom and Bust Cycles

  • What trends do you see in the population curve for Soay Sheep that give its characteristic shape of “boom and bust”?

Survivorship Curves

Population Curves

Population Curves

Population Histograms

Wide base…fast growth

Narrow base….decline

  • What information is given in a population histogram?

  • What shape would a histogram look like if it were representing an declining population? A stabilized population? A young population?

More Histograms

What are these graphs showing?

  • Which country demonstrates

  • a very high reproductive rate?

  • 2. Which country represents a

  • stabilized population?

Show Age Structure

of Pop


  • What do each of the histograms on slides 63 to 64 tell you?

  • What trends do you see in the population curves on slides 63 to 64?

Biotic Potential

  • Max. # of offspring produced in ideal conditions

  • Regulated by four factors:

    • offspring - max #/birth

    • survival capacity – chance that offspring will reach reproductive age

    • procreation - # times/year organism reproduces

    • maturity - age when reproduction begins

Environmental Resistance

  • All factors that limit pop. growth

  • Can be biotic or abiotic

  • Examples include…….

    • Food, water, space, disease, predation, natural disasters, availability of mates, etc

Environmental Resistance

In a




  • Define biotic potential and environmental resistance. Give an example for environmental resistance.

Limiting Factors

  • Affect population size!

    • flood, fire, extreme cold, disease, starvation, predation

  • Law of the minimum

    • various substances are required for growth.

    • the one with the lowest concentration will limit growth ( known as limiting factor)

Limiting Factors can be:

  • Density Independent:

    • affecting pop regardless of # of individuals

    • flood, fire, extreme cold, other abiotic factors

  • Density Dependent:

    • affecting pop & dependent on pop size

    • disease, starvation, predation

  • State the law of the minimum.

  • Define limiting factors.

  • What are some examples of limiting factors?

Name the

Density Dependent Factor!

Pops can also be r or K Selected

r - selected




K - selected




Almost at



K- selected Populations

r- selected Populations

  • Differentiate between r and K-strategies. Give 2 examples of the types of organisms that use each of these strategies.

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