Ecology Part 3 Chapter 4 Population Dynamics

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- Ecology - Part 3 - Chapter 4 Population
Dynamics
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Principles of Population Growth

• A. Population?
• A group of organisms, all of the same species,
  that live in a specific area
• B. Population growth is defined as an increase in
  size of a population over time
• However, populations grow at different rates.

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1. Linear Growth

• If a population grew at a set amount each year,
  say by 10 organisms per year, then the population
  has LINEAR GROWTH
• However, populations normally do not have linear
  growth.

2.
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Question

• Your parents give you two options for allowance
• 1,000 a month
• A penny on the first day of the month that
  doubles to two pennies on the second day and so
  on until the last day of the month
• Which option do you choose?

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.01
.02
.04
.08
.16
.32
1.28
2.56
5.12
10.24
20.48
.64
40.96
163.84
327.68
655.36
1310.72
2621.44
81.92
5242.88
209711.52
41943.04
83886.08
167772.16
335544.32
10,485.76
5368709.12
10,737,418.24 Over 10 million!!
1342177.28
671088.64
2684354.56
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3. Exponential Growth

• If you graph the allowance we just saw on the
  graph it will look like this

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Exponential Growth

• A population that is growing without any limits,
  would have exponential growth
• Meaning that as the population gets bigger, it
  also will grow faster
• ButPopulations cannot keep exponential growth
  for very long, because the environment would not
  be able to support it.

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Exponential Growth
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C. Carrying Capacity

• The environment has a CARRYING CAPACITY for each
  population
• Carrying capacity is the number of organisms that
  an environment can support.
• Once a population reaches its capacity, its
  growth stops.

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D. What can limit growth?

• Limiting factors!
• Different sizes of populations will also have
  different factors affecting them

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1.Density Dependent Factors

• Factors that have an increasing effect as the
  population increase, hence will affect larger
  populations.
• Examples Disease, Competition, Parasites,
  Predators, Food
• These types of factors spread more quickly in
  larger populations.

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Organism Interactions Limit Population Size

• Predation
• Predator consuming prey on a large enough scale
  can have a drastic effect on the size of prey
  population and hence predator population
• Competition
• Density-dependent factor
• Many individuals competing for scarce supplies
• Crowding and Stress
• Stress symptoms include aggression, decrease in
  parental care, decreased fertility, and decreased
  resistance to disease

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2.Density Independent Factors

• Effect any population,
• Size of population not a factor
• ExamplesVolcanic eruption, Temperature, Storms,
  Floods, drought, chemical pesticides,
• pollution

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Predation
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Question

• Do any populations exhibit exponential growth?

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Human Population
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Human Population Growth
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E. World Population

• 1. Census
• Taken in the US once every 10 years
• 2. Demography
• Study of human population size
• Growth Rate
• Age Structure
• Geographic Distribution

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3. Human Population Growth

• Different that other organisms because humans
  consciously change their environment
• Eradication of diseases
• Methods for producing more food
• Technology

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Calculating Growth Rate

• Birthrate
• Number of live births per 1000 population in a
  given year
• Death rate
• Number of deaths per 1000 population in a given
  year
• (Birth Rate Immigration Rate) (Death Rate
  Emigration Rate) Population Growth Rate (PGR)

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4. Growth Rate

• To determine the growth rate, the birth rate is
  compared to the death rate.
• As more people are born, an equal number must
  pass on in order for the growth rate to remain
  level.

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More on Growth Rate

• However, humans are living longer lives our life
  expectancy is getting older all the time.
• 5. Fertility rate is the number of children that
  each woman has on average
• 6. While birthrate is just the number of births
  per 1000 people woman or man.

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7. Age Structures

• Demographers study Age Structures of countries
  This tells how many people are in each age group
• A younger aged population will grow more rapidly
  than an older population.

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8. Immigration vs Emigration

• Immigration is the movement into a country.
• Emigration is the movement out of a country.