Population Dynamics

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PopulationDynamics
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Population Dynamics

• Changes in population size and the factors that
  regulate populations over time.

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Population Density

• The number of individuals per unit area volume.
• Example The number of oak trees per km2 in a
  forest.

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Estimation of Population Size

• 1. Individual counts (not always practical)
• 2. Transects
• 3. Mark-recapture method Lincoln Index
• N marked individual X total catch second time
  recaptured marked individuals
• Example pond turtles 1992 18
• 1993 34 (12)
• 1994 30 (18)

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Estimation of Population Size

• Example pond turtles 1992 18
• 1993 34 (12)
• 1994 30 (18)
• 1992-93 N 18(34) 51 turtles
• 12
• _________________________________________
• 1993-94 N 34(30) 56.7 turtles
• 18
• _________________________________________
• So 51 56.7 107.7 53.9 turtle estimation
• 2

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Dispersion

• The distribution of individuals within
  geographical population boundaries.
• Three examples of dispersion patterns
• 1. Clumped
• 2. Uniform
• 3. Random

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Dispersion Patterns

• 1. Clumped
• a. individuals are aggregated in patches
• b. unequal distribution of resources in the
  environment.
• Example trees around a lake or pond

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Dispersion Patterns

• 2. Uniform
• a. individuals are evenly distributed
• b. interactions among individuals of a
  population
• Example creosote bushes in the desert

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Dispersion Patterns

• 3. Random
• a. unevenly distributed
• b. random dispersion is rare
• Example clams in a mud flat

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Understanding Population Growth

• Exponential Growth Model
• Exponential growth The rate of expansion
  (growth) of a population under ideal conditions.

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Exponential Growth

• Example bacteria

produces a J-shaped curve
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Understanding Population Growth

• 2. Logistic Growth Model
• logistic growth environmental factors that
  restrict the growth of a population
• (called population limiting factors)

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K Carrying Capacity

• The maximum stable population size that a
  particular environment can support over a
  relatively long period of time (K).

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Logistic Growth

• Example turtles in a pond

K
produces a S-shaped curve
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Draw an s-curve and draw a j-curve

• Label each

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Question

• What if?
• N, the number of individuals almost 0
• exponential growth
• N, the number of individuals almost K (carrying
  capacity)
• growth rate is approaching zero Zero
  Population Growth

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Factors That Limit Population Growth

• 1. Density-Dependent Factors
• a. Population-limiting factors whose effects
  depend on population density.
• b. The greater the pop, the greater the effects.
• Examples 1. Limited food supply
• 2. Plagues
• 3. Predation
• 4. War

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Factors That Limit Population Growth

• 2. Density-Independent Factors
• a. Population-limiting factors (abiotic) whose
  occurrence is not affected by pop density.
• b. the greater the pop, the greater the effects
• Examples 1. Earthquakes
• 2. Fires
• 3. Hurricanes
• 4. Freeze in the fall

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Boom and Bust Species

• A rapid increase (boom) in a population followed
  by a sharp decline (bust).
• Examples
• a. Daphnia in a pond

boom
bust
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Boom and Bust Species

• Sometimes species (carnivore) depend on other
  species (prey) for food.
• Example Snowshoe hare and lynx

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Evolution Shapes Life Histories

• Life History
• Series of events from birth through reproduction
  to death.
• Two basic types of life history strategies
• 1. Opportunistic life history
• (r-selected species)
• 2. Equilibrial life history
• (K-selected species)

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1. Opportunistic life history(r-selected species)

• Characteristics
• 1. maturing time short
• 2. life span short
• 3. mortality rate often high
• 4. times female is reproductive usually once
• 5. age at first reproduction early
• 6. size of offspring small
• 7. parental care none
• 8. Size of organism small

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2. Equilibrial life history(K-selected species)

• Characteristics
• 1. maturing time long
• 2. life span long
• 3. mortality rate often low
• 4. times female is reproductive often many
• 5. age at first reproduction late
• 6. size of offspring large
• 7. parental care often extensive
• 8. Size of organism tend to be large

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Life History Examples

• r-selected species
• 1. Garden weeds
• 2. Insects
• 3. Desert flowers
• K-selected species
• 1. Humans
• 2. Apes
• 3. Elephants

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Survivorship Curves

• Type 1 survivorship curve
• High survival rates until old age.
• Example

humans
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Survivorship Curves

• Type 2 survivorship curve
• Intermediate between the extremes.
• Example

squirrel
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Survivorship Curves

• Type 3 survivorship curve
• High mortality rates as larvae but decreased
  mortality at later ages.
• Example

oysters frogs insects
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Human Population Growth

• Age structure
• Proportions of individuals of a population in
  different age groups.
• A typical population has three main age groups
  (age structure).
• 1. Pre-reproductive
• 2. Reproductive
• 3. Post-reproductive

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Age Structure
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Human Population Growth Today

• Human population as a whole is growing
  exponentially.
• Has doubled (doubling-time) three times in the
  last three centuries (doubled the carrying
  capacity several times).
• Is now 6.5 billion, might reach 8 billion by
  2020.

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Question

• What are the reasons for the increase in human
  population?
• Answer
• 1. Improved health
• 2. Technology
• 3. Decreased death rates

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Question

• What is Zero Population Growth (ZPG)?
• Answer
• a. birth rate equals death rate.
• b. intrinsic growth (r) 0

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Question

• What are two ways the human population can reach
  Zero Population Growth?
• 1. Limit the of offspring per couple
• a. Reduces family size
• b. Voluntary contraception
• c. Family planning
• 2. Delay reproduction
• (late 20s instead of early 20s)